Zeolite-encapsulated Ir Single Atom Catalysts toward Efficient and Stable Propane Dehydrogenation

Zeolite-encapsulated Ir Single Atom Catalysts toward Efficient and Stable Propane Dehydrogenation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Zeolite-encapsulated Ir Single Atom Catalysts toward Efficient and Stable Propane Dehydrogenation Guozhu Liu, Mingxia Song, Shaojia Song, Gang Hou, Weijie Li, Xintong Lyu, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6912388/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Single atom precious metal catalysts with maximized metal utilization and versatile electronic-state engineering have shown great potential in heterogeneous catalysis. However, the applications of single atom precious metal catalysts under harsh reaction conditions are significantly restricted due to thermodynamic instability from sintering-driven degradation. We report herein the construction of thermal stable Ir single atoms encapsulated in Ge-substituted S-1 zeolite, namely IrGe@S-1 catalysts, for direct propane dehydrogenation. The optimized IrGe@S-1 catalyst exhibits unprecedent propane dehydrogenation activity with a state-of-the-art propylene formation rate of 1249.2 mol C3H6 g Ir -1 h -1 at 600 o C. It also shows excellent stability for over 800 hours under a high weight hourly space velocity of 20 h -1 (pure propane feeding at 580 o C), producing 9000 ton of propylene with one ton of IrGe@S-1 catalyst without regeneration. The introduction of Ge species promotes the overlap between Ir 5d and O 2p orbital and thereby enhances their interaction via Ir–O–Ge bonds to derive Ir single atom catalysts. Under propane dehydrogenation conditions, propane molecules can induce the dissociation of framework oxygen atoms and the formation of Ir single atoms in low oxidation state. The specific electron-rich Ir single atoms significantly lower the energy barrier of the rate-determining step in propane dehydrogenation and the isolated nature of Ir sites efficiently inhibits the side reaction of over-dehydrogenation, together contributing to the remarkable performance in propane dehydrogenation. This work provides a successful example of stable single atom precious metal catalysts for working under harsh reaction conditions. Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis Physical sciences/Chemistry/Catalysis/Catalytic mechanisms Physical sciences/Nanoscience and technology/Nanoscale materials/Structural properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction An optimal precious metal catalyst should simultaneously achieve maximized atomic utilization efficiency and exceptional reactivity to ensure the economy and efficiency of the reaction process. Single atom catalysts (SACs) have aroused considerable interest owing to their fully exposed active sites with unique geometric and electronic configurations. 1 – 5 For the direct dehydrogenation of light alkanes like propane, the strong endothermic process poses a major challenge to the thermal stability and the regeneration of SACs under high temperature conditions. 6 – 8 Commercial propane dehydrogenation (PDH) catalysts, namely CrO x /Al 2 O 3 and PtSn/Al 2 O 3 , require frequent regeneration due to coke deposition and metal sintering. 9 , 10 To date, the widely studied highly dispersed Pt active sites stabilized by metal additives and/or confinement effects have shown improved dehydrogenation activity, but still limited by the insufficient stability under harsh operating regimes involving prolonged duration and/or elevated space velocities. 11 – 14 These limitations inspire explorations on alternative metal catalysts for efficient and stable propane dehydrogenation. Precious metals, particularly Ir and Rh, potentially stand out as promising alkane dehydrogenation catalysts due to their facile activation of the paraffinic C–H bonds. 15 – 17 Recently, single atom Rh-based catalysts have been reported to exhibit stable high activity in propane dehydrogenation, while the high cost of Rh (205 k $ /lb) might restrict their industrial applications. 16 , 18 Density functional theory (DFT) calculations indicate that atomically dispersed Ir sites in the metallic state can break through the scaling relation between the activation energies for C–H bond cleavage in propane and propylene molecules, which dominates the kinetics of PDH. 19 Thus, the exploration of thermal stable Ir SACs with well-defined local structure and adjustable coordination environment is highly desired for industrial PDH. The stability and catalytic performance of Ir SACs depends largely on the complex interactions between the metal atoms and the supporting materials. 20 , 21 Ma et al. reported that Ir single atoms stabilized by the Ir–C bond on ND@G displayed a high n-butane dehydrogenation rate of 8.8 mol·g Ir −1 ·h − 1 and 95.6% butene selectivity at 450°C in the reaction of butane dehydrogenation, while the atomically dispersed Ir sites were prone to agglomeration under reaction conditions. 17 An alternative approach is to encapsulate Ir metal atoms into zeolite micropores to prevent their structure degradation. 22 – 24 Corma et al. regio-selectively encapsulated isolated Ir atoms in the 10-membered ring (MR) window connecting the neighboring 12-MR supercages in pure silica MWW zeolites. 25 The local strain of isolated Ir species confined in zeolite was closely related to the strength of the metal-zeolite interaction. 24 High temperature reduction treatment led to the formation of clusters, accompanied by the cleavage of Ir–O bonds, thereby facilitating the migration of Ir species. 26 Although substantial progresses have been achieved in the design of Ir SACs outperforming conventional supported catalysts, the controllable synthesis of stable and uniform SACs for working under harsh reaction conditions remains challenging. Herein, we report the successful construction of thermal stable Ir single atoms anchored by Ge-substituted zeolites via a one-pot route for efficient and stable PDH. Compared with monometallic Ir catalyst Ir@S-1, the introduction of Ge species greatly enhances the interaction between Ir and framework adjacent O atoms, thereby stabilizing the Ir single atoms. The optimized IrGe@S-1 catalyst exhibits unprecedent PDH activity and durability under high temperature reaction conditions. The dynamic evolution of Ir active sites is induced by interacting with propane under reaction conditions, generating Ir sites in low oxidation states that can catalyze the cleavage of C–H with low energy barrier. Results Synthesis and characterization of IrGe@S-1 catalyst The MFI zeolite encapsulated Ir SACs were prepared via a one-pot hydrothermal synthesis route with the molar ratio of the mixed gel as 1 SiO 2 : 0.4 TPAOH: 35 H 2 O: 0.0014 H 2 IrCl 6 : x Ge (x ranges from 0 to 0.12). The solid samples after crystallization were washed, dried, reduced by H 2 at 600 o C for 2 h and denoted as Ir@S-1 or IrGe@S-1 with an Ir loading of ~0.2 wt% (IrGe@S-1 refers to sample with initial Ge loading of 10 wt% in the synthesis gel unless specifically stated, i.e. , Ir10Ge@S-1). As shown in Supplementary Figure 1 , all samples show the typical diffraction patterns of MFI topology and type-I N 2 adsorption-desorption isotherms with Brunauer–Emmett–Teller (BET) surface area of 350-400 m 2 g -1 ( Supplementary Figure 2 , Supplementary Table 1 ). Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) images of Ir@S-1 show the hexagonal prism morphology of S-1 zeolite and the presence of Ir nanoclusters of 1-3 nm after high temperature reduction treatment ( Supplementary Figure 3 ). Generally, H 2 reduction leads to the decomposition of Ir precursor and the cleavage of Ir–O bonds, facilitating the agglomeration of metal species. 26 In contrast, no Ir aggregates are visible in IrGe@S-1 although the energy dispersive spectroscopy mapping analyses confirm the presence and even dispersion of Ir and Ge species ( Supplementary Figure 4-5 ). High-resolution aberration corrected high-angle annular dark-field (AC HAADF) STEM was further employed to investigate the location of Ir species encapsulated in zeolite crystallites. As shown in Fig. 1a-d , STEM images of IrGe@S-1 sample along the [010] orientation show the well-defined MFI topology structure with isolated Ir atoms. The images taken from the [001] orientation also demonstrate the presence of isolated Ir atoms ( Fig. 1e-g ). Ge species are inclined to be anchored in the 4-MRs of zeolite framework, giving rise to Ge dimers in a double-bridge configuration according to previous report. 27 Based on the assumption that Ir species interacting with Ge sites and the high resolution images ( Fig. 1 and Supplementary Figure 6-7 ), the isolated Ir atoms are encapsulated around the 5/6-MRs of Ge-substituted S-1 zeolite. The models of isolated Ir atoms anchored by framework oxygen sites are given in Fig. 1h . Ge species play an important role in stabilizing Ir single atoms and also lead to changes in zeolite lattice parameters and morphology ( Supplementary Figure 1 and S5 ). It should be noted that Ge loading in IrGe@S-1 is measured to 1.43 wt% after hydrothermal crystallization, washing and drying ( Supplementary Table 2 ), much lower than 10 wt% in the synthesis gel. Due to the larger atomic radius than Si, Ge atoms could not be fully incorporated into MFI zeolite framework as heteroatoms and excess GeO x species could be removed from the product by simple washing. 28 Fourier transform infrared spectroscopy (FT-IR), 19 F nuclear magnetic resonance (NMR) and quasi in-situ X-ray photoelectron spectroscopy (XPS) were further conducted to investigate the coordination environment of framework Ge sites in zeolite. The FT-IR bands at 1080 and 1228 cm -1 are assigned to the asymmetric stretching of internal and external T–O–T type bridges, the intensities of which decrease upon the incorporation of Ge atoms ( Fig. 1i ). 29 Ge-substituted MFI zeolite shows a new band in the 1030−950 cm -1 region assignable to the asymmetric Si–O–Ge vibrations. 27 The 29 Si NMR spectrum of IrGe@S-1 demonstrate the dominant presence of Q 4 [Si(OSi) 4 ], due to the relatively low loading of framework Ge ( Supplementary Figure 8 ). Previous reports have demonstrated that F – and SiO – defect sites can be reversibly exchanged in the framework of as-synthesized all-silica zeolites. 30 Herein, 19 F NMR spectra were recorded on the Ir@S-1 and IrGe@S-1 after exchanging with F ions ( Fig. 1j ). Compared with Ir@S-1, a new signal appears at -59 ppm for Ge-substituted zeolite, which can be attributed to F ions close to Ge atoms in 4-MRs shared by two fused [4 1 5 2 6 2 ] cages. 30,31 The existing states of Ge in IrGe@S-1 were also analyzed by XPS. After in-situ reduction treatment, Ge 2p signal in IrGe@S-1-H 2 could be fitted into two peaks, allowing correlation with two types of Ge species in different coordination states. The Ge 2p binding energy value at 1220.6 eV is assigned to highly oxidized Ge species anchored by framework oxygen, 32 while the binding energy value at 1218.3 eV is ascribed to Ge atoms in unsaturated coordination with associated Ir atoms ( Fig. 1k ). Based on the above experimental results, Ge-MFI models were constructed as substrates with different numbers of Ge atoms in the 4-MRs of MFI zeolites. Then, the structural stability of Ir single atoms in different MFI substrates was assessed using the formation energy with respect to bulk metallic Ir (ΔE f ). As shown in Supplementary Figure 9 , the formation energies of Ir 1 -Ge x -MFI ( x =0~4, Ir 1 -Ge 0 -MFI refers to Ge-free case) models demonstrate a clear Ge loading dependence, namely progressively more negative with increasing Ge atoms in the 4-MRs. Specifically, the formation energy decreases monotonically from 2.08 eV in the Ge-free Ir 1 -Ge 0 -MFI to 0.89 eV in the single Ge-substituted system (Ge 1 -MFI), and then to a minimum of -0.12 eV in the fully Ge-substituted framework (Ge 4 -MFI). The results suggest that increasing Ge incorporation in 4-MRs significantly enhances the thermodynamic stability of Ir single atoms, with the Ge 4 -MFI configuration providing the most favorable anchoring environment. X-ray absorption near-edge structure spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) were conducted to verify the coordination environment of Ir sites in Ir@S-1 and IrGe@S-1 ( Fig. 2a-b , Supplementary Figure 10-11 ). The white line intensity of the Ir L 3 -edge XANES is close to IrO 2 , corresponding to the highly oxidized Ir species in both Ir@S-1 and IrGe@S-1. The results of EXAFS show distinct peak in R space attributed to Ir–O bonds (2.0 Å) corresponding to the interaction between isolated Ir atoms with framework oxygen atoms ( Supplementary Table 3 ). The Ir–Ir path in Ir@S-1 is consistent with the as-observed nanoclusters. Furthermore, the relative intensity of Ir–O bond is clearly presented in wavelet transformation (WT) of Ir L 3 -edge EXAFS data in Fig. 2c . It confirms the interaction between Ir species and zeolite framework oxygen. All these results demonstrate the formation of well isolated Ir sites in MFI zeolite with the presence of framework Ge species. It should be noted that the Ir species in IrGe@S-1 might be partially reduced by H 2 at 600 o C and quickly oxidized (~+4, Fig. 2a ) upon exposure to air. Nevertheless, the atom-level dispersion of Ir species could be well preserved during the whole process ( Fig. 1 ). The electronic states of Ir sites were further investigated by in-situ FT-IR spectra of CO adsorption and quasi in-situ XPS. As shown in Fig. 2d , the intensity of CO adsorption band on Ir@S-1 is much higher than IrGe@S-1 because CO binds more tightly to the metallic site than to the oxidized M δ + site ( vide infra ). 33 For Ir@S-1, the bands at 2,069 and 1,990 cm - 1 are assigned to the symmetric and asymmetric stretching vibrations of well distributed Ir nanoclusters. 17,34 Due to the substitution of Ge, the ν (CO) frequency increases from 2069 to 2078 cm -1 , attributed to the dicarbonyl species absorbed on positively charged Ir single atoms. 34,35 The enhanced interaction between Ir and framework oxygen atoms results in electron transfer from Ir to O and weakens the feedback π bond of Ir to CO. Quasi in-situ XPS was then performed to further investigate the chemical state of the Ir species after high temperature reduction. The observed Ir 4f signal at 61.2 eV is assigned to mixed chemical states of Ir approaching to the metallic state with lots of highly dispersed Ir nanoclusters in Ir@S-1 ( Fig. 2e ). In the case of IrGe@S-1, the signal of Ir 4f is observed at 61.8 eV, corresponding to the positively charged Ir δ + sites anchored by framework oxygen atoms. These results confirm the uniform dispersion of Ir sites upon the introduction of Ge, and the Ir single atoms carry positive charges due to the enhanced electron transfer to framework oxygen with the presence of Ge. Upon exposure to air under ambient conditions, both metallic Ir clusters (Ir@S-1) and positively charged Ir δ + sites (IrGe@S-1) are quickly transformed to the highly oxidized states ( Fig. 2a ), and therefore, great caution should be taken to identify the real oxidation state of Ir sites in the samples. The interactions between Ir and O were explored by theoretical simulations. The effective Bader charge on Ir atom and the charge density difference resulting from Ir–O interaction were computed. The Bader charge of an isolated Ir site is +0.80 |e|, corresponding to the electron-depletion region around Ir atoms ( Fig. 2f ) and agreeing well with the experimentally observed Ir δ + sites ( Fig. 2e ). From partial density of states (pDOS) analyses, Ir–O bonds are formed by the mixing of Ir s-d orbitals with O d orbitals ( Fig. 2g-h ). In comparison, the hybridization with Ge 4p or 3d orbitals contribute less to the stabilization of Ir atoms ( Fig. 2i ). Therefore, in combination with experimental and theoretical results, the Ir atoms are directly stabilized by framework oxygen atoms of MFI zeolite, and the enhanced overlapping between Ir 5d and O 2p in Ir 1 -Ge 4 -MFI (four Ge atoms in the 4-MRs of MFI) model rationalizes the favorable ΔE f of Ir 1 -Ge 4 -MFI. The Ir–O bond strength was quantitively determined by crystal orbital Hamilton population (COHP) analysis ( Supplementary Figure 12 ). The more negative integral COHP (ICOHP) value in Ir 1 -Ge 4 -MFI reveals the stronger Ir–O binding ( Fig. 2j ). In addition, for various IrGe-MFI models, there is a positive relationship between ICOHP values and ΔE f , which once again validates that the Ir atom is efficiently stabilized by Ir–O–Ge bonds. Catalytic performance in propylene dehydrogenation The as-prepared catalysts were tested in PDH reaction with pure propane feeding under high WHSV of 20 h -1 at 600 °C. As shown in Fig. 3a , IrGe@S-1 shows distinctly higher activity in comparison with Ir@S-1 and Ge@S-1. To optimize the structure of active site in IrGe@S-1, a series of samples with varying initial Ge loadings of 0–20 wt% were prepared and evaluated, with focuses on the specific activity and deactivation rate. As shown in Fig. 3b , the specific activity of IrGe@S-1 is over two times higher than that of Ir@S-1 with the introduction only trace Ge in the synthesis gel (0.25 wt%). With increase in the initial loading of Ge in the synthesis gel (lower than 10 wt%), the deactivation rate of catalyst decreases gradually. The introduction of excess Ge during the crystallization process will increase the number of defect sites and also change the zeolite morphology ( Supplementary Table 1 , Supplementary Figure 13-14 ). As a result, the deactivation rate of catalyst shows the trend of volcanic curve with lowest deactivation rate obtained at initial Ge loading of 10 wt% (1.43 wt% measured in IrGe@S-1 sample, Supplementary Table 2 ). The optimized IrGe@S-1 catalyst was tested in the long-term operation at 580 °C for 800 hours, showing very stable propane conversion of >30% with propylene selectivity of >97% ( Fig. 3c ). It should be noted that a high WHSV of 20 h -1 is employed in our durability test, several times higher that employed in industrial PDH process (UOP, WHSV: 4 h -1 ). Under such circumstance, about 9000 ton of propylene can be produced employing one ton of IrGe@S-1 catalyst without regeneration, which can satisfy the requirement of fixed-bed PDH process and is comparable with the most stable catalyst recently reported like RhIn@S-1 16 and PtSn@S-1 36 . The propylene space-time-yield (STY) value of IrGe@S-1 at 600 °C is calculated to be 1249 mol C3H6 g Ir -1 h -1 , an order of magnitude higher than the other catalysts reported in the literature ( Supplementary Table 4 ), undoubtedly outperforming the state-of-the-art Pt-based catalysts ( Fig. 3d ). On the other hand, IrGe@S-1 is definitely better than other Ir-based zeolite catalysts in terms of both activity and stability ( Supplementary Figure 15 ). To investigate the deactivation and regeneration properties of IrGe@S-1 catalyst, extremely harsh reaction conditions (600 °C, WHSV=300 h -1 ) were employed. As shown in Supplementary Figure 16 , gradual declines in propane conversion could be observed with time-on-stream (propylene selectivity well preserved), indicating the deactivation of catalyst. Fortunately, the catalytic activity of IrGe@S-1 can be fully recovered via simple calcination treatment, demonstrating its robustness for industrial applications. Moreover, IrGe@S-1 shows high activity in the dehydrogenation of ethane and n-butane, producing ethylene and butenes as the target products, respectively ( Supplementary Figure 17-18 ). For the direct dehydrogenation of alkanes, the conversions of alkanes increase as the temperature increase from 450 to 600 °C, which is close to the thermodynamic equilibrium ( Supplementary Figure 19 ). The spent IrGe@S-1 catalyst (after reaction at 600 °C for 18 h) was thoroughly characterized by TEM, thermogravimetry and XPS. As shown in Supplementary Figure 20 , the atomic-level dispersion of Ir species is well maintained in the spent IrGe@S-1 catalyst while carbon deposition on the surface of zeolite is observed, which might inhibit the diffusion of the propane and trigger catalyst deactivation. In contrast, the average size of Ir species in Ir@S-1 grows up to ~6 nm after reaction and partial Ir particles escape from the channel of zeolite, resulting in irreversible catalyst deactivation ( Supplementary Figure 21 ). The amounts of coke on IrGe@S-1 and Ir@S-1 catalyst after PDH reaction for 18 hours is determined to be 3.8 and 3.0 %, respectively, while the amount of coke on IrGe@S-1 after PDH reaction for 800 hours (at 580 o C) is reduced to 3.0 % ( Supplementary Figure 22 ). These observations reveal that carbon deposition is rapid in the early stage of the reaction and the dynamic balance of coke deposition-digestion is important to achieve stable PDH reaction. Reaction mechanism of PDH over IrGe@S-1 catalyst Kinetic analyses of PDH catalyzed by IrGe@S-1 were performed with the elimination of diffusion resistance according to the Madon-Boudart criterion ( Supplementary Figure 23 ). 37 The impacts of propane and H 2 partial pressure on the reaction rates at 460 °C are shown in Supplementary Figure 24 . The fitting curves demonstrate a close to first-order dependence (0.79) on propane and a negative H 2 reaction order of -0.36. 38 It is therefore assumed that the first C–H bond cleavage is the rate-limiting step while other steps are quasi-equilibrated. 39 The relation between reaction rate and propane partial pressure is given as equation S11 in the supplementary information. The kinetic data were obtained at low conversions and fitted to get the rate constant for the first C–H bond cleavage (k 2 ) ( Supplementary Figure 25 ). The apparent activation energy of the dehydrogenation rate coefficient (Ea) determined by Arrhenius plots is 41.5 kJ mol -1 ( Supplementary Figure 26 ), which appears to be distinctly lower than that reported for Pt-based catalysts reported, for example 56.2 kJ mol -1 for PtFe 3 @S-1 and 67.4 kJ mol -1 for PtZn-SPP. 40,41 That is, IrGe@S-1 should be an intrinsically better catalyst for the cleavage of first C–H bond in propane molecules and it can catalyze the PDH reaction at very low reaction temperature of 300-400 °C, as shown in Supplementary Table 5 . Propane temperature-programmed surface reaction (C 3 H 8 -TPSR) profiles reveal that the initial reaction temperature (T 0 ), determined by the appearance of the H 2 signal, over IrGe@S-1 catalysts is slightly lower than that over Ir@S-1 ( Supplementary Figure 27 ). According to the changes in the intensity of propylene signal, the introduction of Ge species promotes the catalytic performance by an order of magnitude. On the other hand, the H 2 signal starts to decline and the CH 4 signal rises rapidly above 600 °C, indicating that the optimal operation temperature of IrGe@S-1 catalyst is below 600 °C. FT-IR spectra of CO adsorption on IrGe@S-1 demonstrate a redshift in CO stretching frequency after reacting with propane (from 2078 to 2067 cm -1 ) ( Fig. 4a ), indicating the enhanced electron donation from Ir atom to CO molecules and corresponding to the metallic electronic state of Ir species. The PDH mechanism over Ir 1 -Ge 4 -MFI model was then investigated using DFT calculations. As shown in Supplementary Figure 28 , the energy barrier of the first and second dehydrogenation step on Ir site of Ir 1 -Ge 4 -MFI is 145.3 and 30.4 kJ mol -1 . After releasing propylene molecules, the generated intermediates *H are bound at the top site of the Ir atom and the oxygen atom with the formation of a hydroxyl group, respectively. These *H intermediates exhibit a strong thermodynamic tendency to be released as H 2 O with breakage of one Ir–O bond, in contrast to direct *H coupling (-57.4 versus 85.2 kJ mol -1 ), thereby generating the oxygen-deficient Ir 1 -Ge 4 -MFI-O vac site. This is consistent with the dynamic transformation introducing localized electron density redistribution at the Ir center, as confirmed by charge density difference diagram in Supplementary Figure 29 . As a result, metallic Ir site with Bader charge of –0.19 |e| is generated in Ir 1 -Ge 4 -MFI-O vac . The above dynamic evolution behavior of Ir 1 site is illustrated in Fig. 4b . In-situ FT-IR spectra of propane dehydrogenation on IrGe@S-1 were recorded to monitor the formation of Ir 1 -Ge 4 -MFI-O vac site in IrGe@S-1 catalyst. As shown in Fig. 4c , the intensity of band at 3720 cm -1 increases distinctly after introducing propane due to the formation of hydroxyl groups. A series of bands between 3500-3800 cm -1 are attributed to H 2 O molecules in the gas phase, the intensities of which increase at the initial stage and start to decrease after forming Ir 1 -Ge 4 -MFI-O vac sites ( Supplementary Figure 30 ). Further calculations were conducted on the in-situ formed Ir 1 -Ge 4 -MFI-O vac site. As shown in Fig. 4d , this Ir 1 -Ge 4 -MFI-O vac site exhibits much better dehydrogenation reactivity with significantly lower energy barrier for the first C–H cleavage (71.4 kJ mol -1 ) in comparison with pristine Ir 1 -Ge 4 -MFI (145.3 kJ mol -1 ), implying that Ir species in the approaching metallic state are more active for C–H bond cleavage ( Supplementary Table 6 ). The kinetic barrier of C–H bond cleavage on Ir 1 -Ge 4 -MFI-O vac is also comparable as that on Ir (111) slab, i.e. , simulating Ir nanoparticles, while there is an obvious difference in *H coupling kinetics between them. Specifically, the *H coupling step requires an energy value of 25.6 kJ mol -1 on Ir 1 -Ge 4 -MFI-O vac site, which is much smaller than the value of 121.5 kJ mol -1 on Ir (111) slab. In this sense, the fast *H removal kinetics on Ir 1 -Ge 4 -MFI-O vac site contribute to the recovery of the active site for propane adsorption and reaction. The rate-degree control analysis was also performed for Ir 1 -Ge 4 -MFI-O vac site using the above DFT-calculated reaction energy data. The results suggest the propane C–H bond cleavage as the rate-determining step at reaction temperature of 600 °C ( Supplementary Figure 31 ), consistent with the experimental results. The propylene desorption energy values over the Ir 1 -Ge 4 -MFI-O vac and the Ir (111) slab were also calculated, as shown in Supplementary Figure 32 . The desorption of propylene on Ir 1 -Ge 4 -MFI-O vac is thermodynamically favorable and the over-dehydrogenation of *C 3 H 6 requires to overcome an energy barrier of 237.3 kJ mol -1 . In contrast, the over-dehydrogenation of *C 3 H 6 is thermodynamically favorable than its desorption on Ir (111) site. Therefore, the side reaction of over-dehydrogenation on large Ir particles will reduce the selectivity toward target product propylene. Combining the kinetic experiments and theoretical calculation results, the first dehydrogenation step is the rate-determining step of PDH reaction and the in-situ formed Ir single atoms in Ir 1 -Ge 4 -MFI-O vac contribute to the superior PDH performance of IrGe@S-1 catalyst. The Ir single atoms in low oxidation states show significant selectivity in activating the C−H bond of propane, and are kept stable even under high temperature conditions. Discussion Previous studies have demonstrated that Ir single atom catalysts show potential in catalyzing alkane dehydrogenation, while the stability of Ir active sites should be significantly improved for working under harsh reaction conditions. The rational modification of Ir active sites might simultaneously enhance the intrinsic reactivity and the high-temperature stability. Herein, thermal stable Ir single atoms anchored by the zeolite framework oxygen atoms have been prepared via a one-pot route, showing superior thermal stability without any metal sintering during high-temperature reduction and dehydrogenation process (Fig. 1 , Supplementary Fig. 20 ). The improved stability is attributed to the incorporation of Ge species into MFI framework at the [4 1 5 2 6 2 ] cages and the overlap between Ir 5d and O 2p orbital by forming Ir–O–Ge bonds (Fig. 2 ). The integral COHP (ICOHP) value in Ir 1 -Ge 4 -MFI further confirms the stronger Ir–O binding with increasing Ge atoms in 4-MRs (Fig. 2 j). Experimentally, IrGe@S-1 exhibits an unprecedent propylene formation rate of 1249.2 mol C3H6 g Ir −1 h − 1 at 600 o C and perfect stability for at least 800 hours in PDH reaction (WHSV = 20 h − 1 , 580 o C). Upon reaction with propane, one framework oxygen in IrGe@S-1 is removed as molecule H 2 O and an isolated Ir site in low oxidation state is formed, namely Ir 1 -Ge 4 -MFI-O vac (Fig. 4 b). The metallic nature of Ir species reduces the energy barrier of the first dehydrogenation step and the isolated nature of Ir sites restricts the over-dehydrogenation reaction, thereby breaking the scaling relationship between activity and selectivity in PDH reaction. This study provides a new perspective to manipulate the interaction of metal and support, showing promise for ultra-stable PDH with SACs. Methods Materials Tetrapropylammonium hydroxide solution (TPAOH, 40 wt% in H 2 O, J&K Scientific Ltd), tetraethyl orthosilicate (TEOS, 99.99% metals basis, Aladdin), hexachloroiridium acid hydrate (H 2 IrCl 6 ·xH 2 O, Ir > 36%, Aladdin), dioxogermane (GeO 2 , 99.99% metals basis, Aladdin) and ethylenediamin (EDA, > 98%, Aladdin). Preparation of Ir@S-1 The synthesis of S-1 zeolite encapsulated monometallic Ir sample (Ir@S-1) was realized by a one-pot method under hydrothermal conditions. The composition of the mixing gel was as follows: 1 SiO 2 : 0.4 TPAOH: 35 H 2 O: 0.0014 H 2 IrCl 6 (molar ratio). Typically, a mixture of TPAOH solution (13 g) and deionized water (15.4 g) was added to a 100 mL round bottom flask, and the homogeneous solution was obtained after 10 minutes of stirring. Subsequently, 8.32 g of TEOS were added dropwise to the mixture, which was then stirred continuously for 6 hours in order to form the desired gel. The metal precursor solution was prepared with H 2 IrCl 6 ·xH 2 O and EDA with a molar ratio of 1:10. The prepared metal solution was then added to the mixing gel and stirred for additional 2 hours. Finally, the gel was transferred to a 100 mL Teflon-lined stainless steel autoclave and crystallized at 170°C for 72 hours. The Ir@S-1 sample was obtained after washing for three times and drying at 80°C for 12 hours. Preparation of IrGe@S-1 The IrGe@S-1 catalysts were prepared by the same method as Ir@S-1. The molar ratio of the mixed gel was 1 SiO 2 : 0.4 TPAOH: 35 H 2 O: 0.0014 H 2 IrCl 6 : x Ge (x ranges from 0 to 0.12) and the as-prepared catalysts were denoted as IrxGe@S-1 (x represents the mass percent of Ge in the feed gel). Firstly, TPAOH solution (13 g) and deionized water (15.4 g) were mixed into a 100 mL round-bottom flask and stirred for 10 minutes. Secondly, TEOs (8.32 g) were added drop by drop while stirring and continued for another 6 hours. The metal precursor solution was prepared with H 2 IrCl 6 ·xH 2 O and EDA, with a molar ratio of 1:10. A quantity of GeO 2 and the prepared metal solution was added to the mixing gel and stirred for a further 2 hours. Finally, the gel was transferred to a 100 mL Teflon-lined stainless steel autoclave and crystallized at 170°C for 72 hours. Following this, the IrGe@S-1 samples were obtained after washing for three times, drying (80°C for 12 hours) and reducing (600°C, 10% H 2 /Ar, 2 h). Declarations Acknowledgment s We thank the National Natural Science Foundation of China (22025802, 22025203, 22308257) for financial support. Shaojia Song thanks the financial support from the Open Project of Key Laboratory of Green Chemical Engineering Process of Ministry of Education (GCP2024005). We thank the staff members of BL17B beamline (https://cstr.cn/31129.02.NFPS.BL17B) at the National Facility for Protein Science in Shanghai (https://cstr.cn/31129.02.NFPS), for technical support in XAFS data collection and analysis. Author contributions G.L. contributed to conceptualization, investigation, resources, supervision, project administration, writing – review and editing. M.S. contributed to investigation, methodology, data curation, formal analysis, writing – original draft and review. S.S. contributed to theoretical calculations, writing – review and editing. G.H. contributed to investigation, methodology, data curation. W.L. contributed to data curation, formal analysis. X.L. contributed to methodology, data curation, formal analysis. J.L. contributed to supervision, writing – review and editing. C.Y. contributed to investigation, methodology, formal analysis. S.F. contributed to investigation, methodology. R.W. contributed to investigation, data curation. B.Z. contributed to conceptualization, investigation, supervision, writing – review and editing. L.L. contributed to supervision, data curation, writing – review and editing. § Mingxia Song and Shaojia Song contribute equally to this paper. Competing i nterest s The authors declare no competing financial interest. Data availability All data presented here are available with the paper or from the corresponding authors. Source data are provided with this paper. Additional information The detailed characterizations and experiments data are available in supplementary information (DOC). Author Information Corresponding Author Guozhu Liu - Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China. Haihe Laboratory of Sustainable Chemical Transformations, Tianjin 300192, China. Email: [email protected] Landong Li - Key Laboratory of Advanced Energy Materials Chemistry of Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071, P.R. China Email: [email protected] Bofeng Zhang - Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China. Email: [email protected] References Qiao, B. et al. Single-atom catalysis of CO oxidation using Pt 1 /FeO x . Nat. Chem 3, 634-641, (2011). Wang, A. et al. Heterogeneous single-atom catalysis. Nat. Rev. Chem 2, 65-81, (2018). Liang, X. et al. The progress and outlook of metal single-atom-site catalysis. J. Am. Chem. Soc. 144, 18155-18174, (2022). Shi, X. et al. Metal–support frontier orbital interactions in single-atom catalysis. Nature 640, 668–675, (2025). Zhou, Y. et al. Peripheral-nitrogen effects on the Ru 1 centre for highly efficient propane dehydrogenation. Nat. Catal. 5, 1145-1156, (2022). Dou, X. et al. Size-dependent structural features of subnanometer PtSn catalysts encapsulated in zeolite for alkane dehydrogenation. ACS Catal. 14, 2859-2871, (2024). Song, M. et al. Dynamic stable Pt 13 clusters anchored on isolated ZnO x nanorafts for efficient cycloparaffin dehydrogenation. Appl. Catal., B 363, 124787, (2025). Zhou, H. et al. Cobaltosilicate zeolite beyond platinum catalysts for propane dehydrogenation. Nat. Catal. , (2025). Chen, S. et al. Propane dehydrogenation: catalyst development, new chemistry, and emerging technologies. Chem. Soc. Rev 50, 3315-3354, (2021). Monai, M. et al. Propane to olefins tandem catalysis: a selective route towards light olefins production. Chem. Soc. Rev 50, 11503-11529, (2021). Ma, Y. et al. Germanium-enriched double-four-membered-ring units inducing zeolite-confined subnanometric Pt clusters for efficient propane dehydrogenation. Nat. Catal. 6, 506–518, (2023). Zhang, B. et al. Boosting propane dehydrogenation over PtZn encapsulated in an epitaxial high-crystallized zeolite with a low surface barrier. ACS Catal. 12, 1310-1314, (2022). Sun, Q. et al. Subnanometer bimetallic platinum-zinc clusters in zeolites for propane dehydrogenation. Angew. Chem. Int. Ed 132, 19618-19627, (2020). Ryoo, R. et al. Rare-earth-platinum alloy nanoparticles in mesoporous zeolite for catalysis. Nature 585, 221-224, (2020). German, E. D. & Sheintuch, M. Predicting CH 4 dissociation kinetics on metals: trends, sticking coefficients, H tunneling, and kinetic isotope effect. J. Phys. Chem. 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Li, X. & Liu, L. Hydrothermally stable zeolite-encapsulated metal catalyst promoted by framework Sn species. ACS Catal. 15, 403-421, (2025). Gu, J. et al. Platinum nanoparticles encapsulated in MFI zeolite crystals by a two-step dry gel conversion method as a highly selective hydrogenation catalyst. ACS Catal. 5, 6893-6901, (2015). Liu, L. et al. Direct assessment of confinement effect in zeolite-encapsulated subnanometric metal species. Nat. Commun. 13, 821, (2022). Liu, L. et al. Regioselective generation of single-site iridium atoms and their evolution into stabilized subnanometric iridium clusters in MWW zeolite. Angew. Chem. Int. Ed 59, 15695-15702, (2020). Lu, J. et al. Hydrogen activation and metal hydride formation trigger cluster formation from supported iridium complexes. J. Am. Chem. Soc. 134, 5022-5025, (2012). Dib, E. et al. Germanium atoms exceed the tetrahedral coordination in MFI zeolite. J. Am. Chem. Soc. 147, 3274-3282, (2025). Parmar, D. et al. Unique role of GeO 2 as a noninvasive promoter of nano-sized zeolite crystals. Adv. Mater 34, 2205885, (2022). van de Water, L. G. A. et al. Ge-ZSM-5: the simultaneous incorporation of Ge and Al into ZSM-5 using a parallel synthesis approach. J. Phys. Chem. B 107, 10423-10430, (2003). Liu, X. et al. Evidence for F − /SiO − anion exchange in the framework of as-synthesized all-silica zeolites. Angew. Chem. Int. Ed 50, 5900-5903, (2011). Vidal-Moya, J. A. et al. Distribution of fluorine and germanium in a new zeolite structure ITQ-13 studied by 19 F nuclear magnetic resonance. Chem. Mater. 15, 3961-3963, (2003). Prabhakaran, K. & Ogino, T. Oxidation of Ge(100) and Ge(111) surfaces: an UPS and XPS study. Surf. Sci 325, 263-271, (1995). Guo, Y. et al. Ensemble effect for single-atom, small cluster and nanoparticle catalysts. Nat. Catal. 5, 766-776, (2022). Zhao, A. & Gates, B. C. Hexairidium Clusters Supported on γ-Al 2 O 3 : Synthesis, Structure, and Catalytic Activity for Toluene Hydrogenation. J. Am. Chem. Soc. 118, 2458-2469, (1996). Lu, J. et al. Oxide- and zeolite-supported isostructural Ir(C 2 H 4 ) 2 complexes: molecular-level observations of electronic effects of supports as ligands. Langmuir 28, 12806-12815, (2012). Xu, Z. et al. Pt migration-lockup in zeolite for stable propane dehydrogenation catalyst. (2025) https://doi.org/10.1038/s41586-025-09168-8. Zhang, M. et al. How to measure the reaction performance of heterogeneous catalytic reactions reliably. Joule 3, 2876-2883, (2019). Alghannam, A. & Bell, A. T. Effects of cofeeding hydrogen on propane dehydrogenation catalyzed by isolated iron sites incorporated into dealuminated BEA. J. Am. Chem. Soc. 147, 1677–1693, (2025). Qi, L. et al. Propane dehydrogenation catalyzed by isolated Pt atoms in ≡SiOZn–OH nests in dealuminated zeolite Beta. J. Am. Chem. Soc. 143, 21364-21378, (2021). Xu, M. et al. Zinc migration mediates isolated [PtFe 3 ] in zeolite for propane dehydrogenation. ACS Catal. 15, 3215-3226, (2025). Qi, L. et al. Dehydrogenation of propane and n-Butane catalyzed by isolated PtZn 4 sites supported on self-pillared zeolite pentasil nanosheets. ACS Catal. 12, 11177-11189, (2022). Additional Declarations There is NO Competing Interest. Supplementary Files Supplementaryinformation.docx Supplementary information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6912388","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":488520507,"identity":"144133da-3d36-46d3-9990-080d826efcab","order_by":0,"name":"Guozhu Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsElEQVRIiWNgGAWjYDACdsYGhg8MbCCmAZFamBkbGGckkKYFiHgSGEjQIu/M3CZt+4MvsYG9eZsEQ80dwloMDzO2SecksCU28Bwrk2A49owILc0wLRI5ZhKMDYeJ1GIB0iL/hkgt8sxALQxgW3iI1GLAzNhs2ZPGZtzGk1ZskXCMGFva2x/e+GFzTLaf/fDGGx9qiLHlAJg6Bon/BMIagLY0gKkaYtSOglEwCkbBSAUA2lYxcZc+KiYAAAAASUVORK5CYII=","orcid":"","institution":"Tianjin University","correspondingAuthor":true,"prefix":"","firstName":"Guozhu","middleName":"","lastName":"Liu","suffix":""},{"id":488520508,"identity":"e053dfa1-347f-47b4-8c3b-fc4677f8cc0b","order_by":1,"name":"Mingxia Song","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Mingxia","middleName":"","lastName":"Song","suffix":""},{"id":488520509,"identity":"812e1dac-0679-4e8a-9ed5-b0d73ab91384","order_by":2,"name":"Shaojia Song","email":"","orcid":"","institution":"Taiyuan University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Shaojia","middleName":"","lastName":"Song","suffix":""},{"id":488520510,"identity":"d1190a53-f74f-4feb-92ac-b045ea39b458","order_by":3,"name":"Gang Hou","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Gang","middleName":"","lastName":"Hou","suffix":""},{"id":488520511,"identity":"37945125-446f-4e76-beee-6947a55b1315","order_by":4,"name":"Weijie Li","email":"","orcid":"","institution":"Nankai University","correspondingAuthor":false,"prefix":"","firstName":"Weijie","middleName":"","lastName":"Li","suffix":""},{"id":488520512,"identity":"0c4a6000-1cd3-4b46-8e7f-7a1ab065ed08","order_by":5,"name":"Xintong Lyu","email":"","orcid":"","institution":"Nankai University","correspondingAuthor":false,"prefix":"","firstName":"Xintong","middleName":"","lastName":"Lyu","suffix":""},{"id":488520513,"identity":"2c3984a4-430e-432b-ab4f-9337a29061f2","order_by":6,"name":"Jiafei Lyu","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Jiafei","middleName":"","lastName":"Lyu","suffix":""},{"id":488520514,"identity":"d6b39651-fb8a-46f1-afb6-44c0108b868f","order_by":7,"name":"Caihua Yang","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Caihua","middleName":"","lastName":"Yang","suffix":""},{"id":488520515,"identity":"e1e1f26d-2481-48ed-a697-1bcd8371c122","order_by":8,"name":"Shangzhen Feng","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Shangzhen","middleName":"","lastName":"Feng","suffix":""},{"id":488520516,"identity":"9b13140a-dc2e-4a7d-87b7-fb2dbee88b42","order_by":9,"name":"Ruiyang Wang","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Ruiyang","middleName":"","lastName":"Wang","suffix":""},{"id":488520517,"identity":"1f56fd4c-71fb-404a-a5bc-93840140f016","order_by":10,"name":"Bofeng Zhang","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Bofeng","middleName":"","lastName":"Zhang","suffix":""},{"id":488520518,"identity":"6b09d1a7-18af-49b6-bc22-4df91038c097","order_by":11,"name":"Landong Li","email":"","orcid":"https://orcid.org/0000-0003-0998-4061","institution":"Nankai University","correspondingAuthor":false,"prefix":"","firstName":"Landong","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2025-06-17 08:57:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6912388/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6912388/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87695944,"identity":"7911665e-d920-4e44-983f-a3e80dba9212","added_by":"auto","created_at":"2025-07-28 06:04:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1174841,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLocation of isolated Ir sites and Ge species within MFI zeolite.\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) AC HAADF-STEM image of IrGe@S-1 catalyst along the [010] orientation, showing the atomically dispersed Ir species in MFI zeolite; (\u003cstrong\u003eb-c\u003c/strong\u003e) Enlarged and colored view of (\u003cstrong\u003ea\u003c/strong\u003e); (\u003cstrong\u003ed\u003c/strong\u003e) Model of MFI zeolite with isolated Ir atoms anchored by Ge atoms in the 4-MRs of S-1 zeolite observed along the [010] orientation; (\u003cstrong\u003ee\u003c/strong\u003e) AC HAADF-STEM image of IrGe@S-1 catalyst along the [001] orientation; (\u003cstrong\u003ef-g\u003c/strong\u003e) Enlarged and colored view of (\u003cstrong\u003ed\u003c/strong\u003e); (\u003cstrong\u003eh\u003c/strong\u003e) Model of MFI zeolite with isolated Ir atoms anchored by Ge atoms in the 4-MRs of zeolite from top view; (\u003cstrong\u003ei\u003c/strong\u003e) FT-IR spectra of Ir@S-1 and IrGe@S-1 samples; (\u003cstrong\u003ej\u003c/strong\u003e)\u003csup\u003e 19\u003c/sup\u003eF NMR spectra of Ir@S-1 and IrGe@S-1 after F ions exchange; (\u003cstrong\u003ek\u003c/strong\u003e) \u003cem\u003eQuasi in-situ\u003c/em\u003e Ge 2p\u003csup\u003e \u003c/sup\u003eXPS of IrGe@S-1 during H\u003csub\u003e2\u003c/sub\u003e reduction (IrGe@S-1-H\u003csub\u003e2\u003c/sub\u003e).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6912388/v1/c6e06f7badf813cea402590e.png"},{"id":87695940,"identity":"d6169eec-7807-46b2-a92e-9bd4ff560533","added_by":"auto","created_at":"2025-07-28 06:04:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":490491,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIdentification of Ir single sites in MFI zeolite\u003c/strong\u003e (\u003cstrong\u003ea\u003c/strong\u003e) Ir L\u003csub\u003e3\u003c/sub\u003e-edge XANES spectra of Ir foil, IrO\u003csub\u003e2\u003c/sub\u003e, Ir@S-1 and IrGe@S-1 samples; (\u003cstrong\u003eb\u003c/strong\u003e) Ir L\u003csub\u003e3\u003c/sub\u003e-edge EXAFS data of Ir foil, IrO\u003csub\u003e2\u003c/sub\u003e, Ir@S-1 and IrGe@S-1 samples, magnitude of the FT k\u003csup\u003e3\u003c/sup\u003e-weighted; (\u003cstrong\u003ec\u003c/strong\u003e) The wavelet transformation of Ir L\u003csub\u003e3\u003c/sub\u003e-edge EXAFS data of Ir@S-1 and IrGe@S-1 samples; (\u003cstrong\u003ed\u003c/strong\u003e) \u003cem\u003eIn-situ\u003c/em\u003e FT-IR spectra of CO adsorption on Ir@S-1 and IrGe@S-1 reduced by H\u003csub\u003e2\u003c/sub\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC; (\u003cstrong\u003ee\u003c/strong\u003e) \u003cem\u003eQuasi in-situ \u003c/em\u003eIr\u003csub\u003e \u003c/sub\u003e4f XPS of Ir@S-1 and IrGe@S-1 reduced by H\u003csub\u003e2\u003c/sub\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC; (\u003cstrong\u003ef\u003c/strong\u003e) Top view of the geometry and charge density difference for Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI model (Ir anchored by 4 Ge atoms in the 4-MRs of MFI zeolite). The yellow and cyan regions represent electron accumulation and depletion, respectively; The projected density of states: (\u003cstrong\u003eg\u003c/strong\u003e) O 2p states and Ir 5d, 6s states in Ge-free Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e0\u003c/sub\u003e-MFI model, (\u003cstrong\u003eh\u003c/strong\u003e) O 2p states and Ir 5d, 6s states in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI model, (\u003cstrong\u003ei\u003c/strong\u003e) Ge 4p, 3d states and Ir 5d, 6s states in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI model. (\u003cstrong\u003ej\u003c/strong\u003e) Ir–O bond binding energy versus ICOHP values of Ir–O interactions in various Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e-MFI model.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6912388/v1/a51ba980ec01549687093a1c.png"},{"id":87695943,"identity":"5ba749ed-8330-41a6-9d02-32b36542b871","added_by":"auto","created_at":"2025-07-28 06:04:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":232336,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCatalytic performance in propane dehydrogenation \u003c/strong\u003e(\u003cstrong\u003ea\u003c/strong\u003e) Propane conversion (solid symbols) and propylene selectivity (empty symbols) over Ir@S-1, Ge@S-1 and IrGe@S-1 catalysts. Reaction conditions: T=600 °C, pure C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003e, WHSV=20 h\u003csup\u003e-1\u003c/sup\u003e; (\u003cstrong\u003eb\u003c/strong\u003e) The specific activity and deactivation rate constant of IrGe@S-1 catalysts as a function of initial Ge loading in the synthesis gel. Reaction conditions: T=600 °C, pure C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003e, WHSV=20 h\u003csup\u003e-1\u003c/sup\u003e; (\u003cstrong\u003ec\u003c/strong\u003e) Stability test of IrGe@S-1 catalyst in propane dehydrogenation. Reaction conditions: T=580 °C, pure C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003e, WHSV=20 h\u003csup\u003e-1\u003c/sup\u003e; (\u003cstrong\u003ed\u003c/strong\u003e) Plots of the STY against the deactivation rate constant of IrGe@S-1 and other precious metal catalysts reported in the literature.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6912388/v1/41a6c8bbe313d5adcf4e6525.png"},{"id":87696520,"identity":"4a5cbcb6-55be-4ea9-9a39-887887db5344","added_by":"auto","created_at":"2025-07-28 06:12:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":363430,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEvolution of active sites and\u003c/strong\u003e \u003cstrong\u003ereaction mechanism of PDH reaction\u003c/strong\u003e. (\u003cstrong\u003ea\u003c/strong\u003e) FT-IR spectra of CO adsorption on IrGe@S-1 and IrGe@S-1 after reacting with propane (IrGe@S-1-C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003e); (\u003cstrong\u003eb\u003c/strong\u003e) Top view of the propane reaction on the Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI site and the formation of Ir\u003csub\u003e1\u003c/sub\u003e site in low oxidation state; (\u003cstrong\u003ec\u003c/strong\u003e) \u003cem\u003eIn-situ\u003c/em\u003e FT-IR spectra of propane dehydrogenation on IrGe@S-1 at 550 °C; (\u003cstrong\u003ed\u003c/strong\u003e) Calculated potential energy diagram for the PDH reaction on Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e and Ir(111) within the MFI framework, with the configurations of reaction intermediates.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6912388/v1/d75284f1a649b751c9a0315a.png"},{"id":87696686,"identity":"58642126-68b6-4383-b28a-71aa661bf2b9","added_by":"auto","created_at":"2025-07-28 06:20:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3531520,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6912388/v1/141761a5-21e9-4d2d-b5b0-cf6e05ef374e.pdf"},{"id":87695945,"identity":"8db0b2fd-5c05-438f-8359-232e112fae06","added_by":"auto","created_at":"2025-07-28 06:04:56","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10269296,"visible":true,"origin":"","legend":"Supplementary information","description":"","filename":"Supplementaryinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6912388/v1/e92dd9ad74f9f484b74fab31.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Zeolite-encapsulated Ir Single Atom Catalysts toward Efficient and Stable Propane Dehydrogenation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAn optimal precious metal catalyst should simultaneously achieve maximized atomic utilization efficiency and exceptional reactivity to ensure the economy and efficiency of the reaction process. Single atom catalysts (SACs) have aroused considerable interest owing to their fully exposed active sites with unique geometric and electronic configurations.\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e For the direct dehydrogenation of light alkanes like propane, the strong endothermic process poses a major challenge to the thermal stability and the regeneration of SACs under high temperature conditions.\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e Commercial propane dehydrogenation (PDH) catalysts, namely CrO\u003csub\u003ex\u003c/sub\u003e/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and PtSn/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, require frequent regeneration due to coke deposition and metal sintering.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e To date, the widely studied highly dispersed Pt active sites stabilized by metal additives and/or confinement effects have shown improved dehydrogenation activity, but still limited by the insufficient stability under harsh operating regimes involving prolonged duration and/or elevated space velocities.\u003csup\u003e\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e These limitations inspire explorations on alternative metal catalysts for efficient and stable propane dehydrogenation.\u003c/p\u003e\u003cp\u003ePrecious metals, particularly Ir and Rh, potentially stand out as promising alkane dehydrogenation catalysts due to their facile activation of the paraffinic C\u0026ndash;H bonds.\u003csup\u003e\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Recently, single atom Rh-based catalysts have been reported to exhibit stable high activity in propane dehydrogenation, while the high cost of Rh (205 k\u003cspan\u003e$\u003c/span\u003e/lb) might restrict their industrial applications.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e Density functional theory (DFT) calculations indicate that atomically dispersed Ir sites in the metallic state can break through the scaling relation between the activation energies for C\u0026ndash;H bond cleavage in propane and propylene molecules, which dominates the kinetics of PDH.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e Thus, the exploration of thermal stable Ir SACs with well-defined local structure and adjustable coordination environment is highly desired for industrial PDH.\u003c/p\u003e\u003cp\u003eThe stability and catalytic performance of Ir SACs depends largely on the complex interactions between the metal atoms and the supporting materials.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e Ma \u003cem\u003eet al.\u003c/em\u003e reported that Ir single atoms stabilized by the Ir\u0026ndash;C bond on ND@G displayed a high n-butane dehydrogenation rate of 8.8 mol\u0026middot;g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e\u0026middot;h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 95.6% butene selectivity at 450\u0026deg;C in the reaction of butane dehydrogenation, while the atomically dispersed Ir sites were prone to agglomeration under reaction conditions.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e An alternative approach is to encapsulate Ir metal atoms into zeolite micropores to prevent their structure degradation.\u003csup\u003e\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e Corma \u003cem\u003eet al.\u003c/em\u003e regio-selectively encapsulated isolated Ir atoms in the 10-membered ring (MR) window connecting the neighboring 12-MR supercages in pure silica MWW zeolites.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e The local strain of isolated Ir species confined in zeolite was closely related to the strength of the metal-zeolite interaction.\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e High temperature reduction treatment led to the formation of clusters, accompanied by the cleavage of Ir\u0026ndash;O bonds, thereby facilitating the migration of Ir species.\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e Although substantial progresses have been achieved in the design of Ir SACs outperforming conventional supported catalysts, the controllable synthesis of stable and uniform SACs for working under harsh reaction conditions remains challenging.\u003c/p\u003e\u003cp\u003eHerein, we report the successful construction of thermal stable Ir single atoms anchored by Ge-substituted zeolites \u003cem\u003evia\u003c/em\u003e a one-pot route for efficient and stable PDH. Compared with monometallic Ir catalyst Ir@S-1, the introduction of Ge species greatly enhances the interaction between Ir and framework adjacent O atoms, thereby stabilizing the Ir single atoms. The optimized IrGe@S-1 catalyst exhibits unprecedent PDH activity and durability under high temperature reaction conditions. The dynamic evolution of Ir active sites is induced by interacting with propane under reaction conditions, generating Ir sites in low oxidation states that can catalyze the cleavage of C\u0026ndash;H with low energy barrier.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eSynthesis and characterization of IrGe@S-1 catalyst\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe MFI zeolite encapsulated Ir SACs were prepared \u003cem\u003evia\u003c/em\u003e a one-pot hydrothermal synthesis route with the molar ratio of the mixed gel as 1 SiO\u003csub\u003e2\u003c/sub\u003e: 0.4 TPAOH: 35 H\u003csub\u003e2\u003c/sub\u003eO: 0.0014 H\u003csub\u003e2\u003c/sub\u003eIrCl\u003csub\u003e6\u003c/sub\u003e: x Ge (x ranges from 0 to 0.12). The solid samples after crystallization were washed, dried, reduced by H\u003csub\u003e2\u003c/sub\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC for 2 h and denoted as Ir@S-1 or IrGe@S-1 with an Ir loading of ~0.2 wt% (IrGe@S-1 refers to sample with initial Ge loading of 10 wt% in the synthesis gel unless specifically stated, \u003cem\u003ei.e.\u003c/em\u003e, Ir10Ge@S-1). As shown in \u003cstrong\u003eSupplementary Figure 1\u003c/strong\u003e, all samples show the typical diffraction patterns of MFI topology and type-I N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms with Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) surface area of 350-400 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e-1\u003c/sup\u003e (\u003cstrong\u003eSupplementary Figure 2\u003c/strong\u003e, \u003cstrong\u003eSupplementary Table 1\u003c/strong\u003e). Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) images of Ir@S-1 show the hexagonal prism morphology of S-1 zeolite and the presence of Ir nanoclusters of 1-3 nm after high temperature reduction treatment (\u003cstrong\u003eSupplementary Figure 3\u003c/strong\u003e). Generally, H\u003csub\u003e2\u003c/sub\u003e reduction leads to the decomposition of Ir precursor and the cleavage of Ir\u0026ndash;O bonds, facilitating the agglomeration of metal species.\u003csup\u003e26\u003c/sup\u003e In contrast, no Ir aggregates are visible in IrGe@S-1 although the energy dispersive spectroscopy mapping analyses confirm the presence and even dispersion of Ir and Ge species (\u003cstrong\u003eSupplementary Figure 4-5\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eHigh-resolution aberration corrected high-angle annular dark-field (AC HAADF) STEM was further employed to investigate the location of Ir species encapsulated in zeolite crystallites. As shown in \u003cstrong\u003eFig. 1a-d\u003c/strong\u003e, STEM images of IrGe@S-1 sample along the [010] orientation show the well-defined MFI topology structure with isolated Ir atoms. The images taken from the [001] orientation also demonstrate the presence of isolated Ir atoms (\u003cstrong\u003eFig. 1e-g\u003c/strong\u003e). Ge species are inclined to be anchored in the 4-MRs of zeolite framework, giving rise to Ge dimers in a double-bridge configuration according to previous report.\u003csup\u003e27\u003c/sup\u003e Based on the assumption that Ir species interacting with Ge sites and the high resolution images (\u003cstrong\u003eFig. 1\u003c/strong\u003e and \u003cstrong\u003eSupplementary Figure 6-7\u003c/strong\u003e), the isolated Ir atoms are encapsulated around the 5/6-MRs of Ge-substituted S-1 zeolite. The models of isolated Ir atoms anchored by framework oxygen sites are given in \u003cstrong\u003eFig. 1h\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eGe species play an important role in stabilizing Ir single atoms and also lead to changes in zeolite lattice parameters and morphology (\u003cstrong\u003eSupplementary Figure 1\u003c/strong\u003e and \u003cstrong\u003eS5\u003c/strong\u003e). It should be noted that Ge loading in IrGe@S-1 is measured to 1.43 wt% after hydrothermal crystallization, washing and drying (\u003cstrong\u003eSupplementary Table 2\u003c/strong\u003e), much lower than 10 wt% in the synthesis gel. Due to the larger atomic radius than Si, Ge atoms could not be fully incorporated into MFI zeolite framework as heteroatoms and excess GeO\u003csub\u003ex\u003c/sub\u003e species could be removed from the product by simple washing.\u003csup\u003e28\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eFourier transform infrared spectroscopy (FT-IR), \u003csup\u003e19\u003c/sup\u003eF nuclear magnetic resonance (NMR) and \u003cem\u003equasi\u003c/em\u003e\u003cem\u003e\u0026nbsp;in-situ\u003c/em\u003e X-ray photoelectron spectroscopy (XPS) were further conducted to investigate the coordination environment of framework Ge sites in zeolite. The FT-IR bands at 1080 and 1228 cm\u003csup\u003e-1\u003c/sup\u003e are assigned to the asymmetric stretching of internal and external T\u0026ndash;O\u0026ndash;T type bridges, the intensities of which decrease upon the incorporation of Ge atoms (\u003cstrong\u003eFig. 1i\u003c/strong\u003e).\u003csup\u003e29\u003c/sup\u003e Ge-substituted MFI zeolite shows a new band in the 1030\u0026minus;950 cm\u003csup\u003e-1\u003c/sup\u003e region assignable to the asymmetric Si\u0026ndash;O\u0026ndash;Ge vibrations.\u003csup\u003e27\u003c/sup\u003e The \u003csup\u003e29\u003c/sup\u003eSi NMR spectrum of IrGe@S-1 demonstrate the dominant presence of Q\u003csub\u003e4\u003c/sub\u003e[Si(OSi)\u003csub\u003e4\u003c/sub\u003e], due to the relatively low loading of framework Ge (\u003cstrong\u003eSupplementary Figure 8\u003c/strong\u003e). Previous reports have demonstrated that F\u003csup\u003e\u0026ndash;\u003c/sup\u003e and SiO\u003csup\u003e\u0026ndash;\u003c/sup\u003e defect sites can be reversibly exchanged in the framework of as-synthesized all-silica zeolites.\u003csup\u003e30\u003c/sup\u003e Herein, \u003csup\u003e19\u003c/sup\u003eF NMR spectra were recorded on the Ir@S-1 and IrGe@S-1 after exchanging with F ions (\u003cstrong\u003eFig. 1j\u003c/strong\u003e). Compared with Ir@S-1, a new signal appears at -59 ppm for Ge-substituted zeolite, which can be attributed to F ions close to Ge atoms in 4-MRs shared by two fused [4\u003csup\u003e1\u003c/sup\u003e5\u003csup\u003e2\u003c/sup\u003e6\u003csup\u003e2\u003c/sup\u003e] cages.\u003csup\u003e30,31\u003c/sup\u003e The existing states of Ge in IrGe@S-1 were also analyzed by XPS. After \u003cem\u003ein-situ\u003c/em\u003e reduction treatment, Ge 2p signal in IrGe@S-1-H\u003csub\u003e2\u003c/sub\u003e could be fitted into two peaks, allowing correlation with two types of Ge species in different coordination states. The Ge 2p binding energy value at 1220.6 eV is assigned to highly oxidized Ge species anchored by framework oxygen,\u003csup\u003e32\u003c/sup\u003e while the binding energy value at 1218.3 eV is ascribed to Ge atoms in unsaturated coordination with associated Ir atoms (\u003cstrong\u003eFig. 1k\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eBased on the above experimental results, Ge-MFI models were constructed as substrates with different numbers of Ge atoms in the 4-MRs of MFI zeolites. Then, the structural stability of Ir single atoms in different MFI substrates was assessed using the formation energy with respect to bulk metallic Ir (\u0026Delta;E\u003csub\u003ef\u003c/sub\u003e). As shown in \u003cstrong\u003eSupplementary Figure 9\u003c/strong\u003e, the formation energies of Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003cem\u003e\u003csub\u003ex\u003c/sub\u003e\u003c/em\u003e-MFI (\u003cem\u003ex\u003c/em\u003e=0~4, Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e0\u003c/sub\u003e-MFI refers to Ge-free case) models demonstrate a clear Ge loading dependence, namely progressively more negative with increasing Ge atoms in the 4-MRs. Specifically, the formation energy decreases monotonically from 2.08 eV in the Ge-free Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e0\u003c/sub\u003e-MFI to 0.89 eV in the single Ge-substituted system (Ge\u003csub\u003e1\u003c/sub\u003e-MFI), and then to a minimum of -0.12 eV in the fully Ge-substituted framework (Ge\u003csub\u003e4\u003c/sub\u003e-MFI). The results suggest that increasing Ge incorporation in 4-MRs significantly enhances the thermodynamic stability of Ir single atoms, with the Ge\u003csub\u003e4\u003c/sub\u003e-MFI configuration providing the most favorable anchoring environment.\u003c/p\u003e\n\u003cp\u003eX-ray absorption near-edge structure spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) were conducted to verify the coordination environment of Ir sites in Ir@S-1 and IrGe@S-1 (\u003cstrong\u003eFig. 2a-b\u003c/strong\u003e, \u003cstrong\u003eSupplementary Figure 10-11\u003c/strong\u003e). The white line intensity of the Ir L\u003csub\u003e3\u003c/sub\u003e-edge XANES is close to IrO\u003csub\u003e2\u003c/sub\u003e, corresponding to the highly oxidized Ir species in both Ir@S-1 and IrGe@S-1. The results of EXAFS show distinct peak in R space attributed to Ir\u0026ndash;O bonds (2.0 \u0026Aring;) corresponding to the interaction between isolated Ir atoms with framework oxygen atoms (\u003cstrong\u003eSupplementary Table 3\u003c/strong\u003e). The Ir\u0026ndash;Ir path in Ir@S-1 is consistent with the as-observed nanoclusters. Furthermore, the relative intensity of Ir\u0026ndash;O bond is clearly presented in wavelet transformation (WT) of Ir L\u003csub\u003e3\u003c/sub\u003e-edge EXAFS data in \u003cstrong\u003eFig. 2c\u003c/strong\u003e. It confirms the interaction between Ir species and zeolite framework oxygen. All these results demonstrate the formation of well isolated Ir sites in MFI zeolite with the presence of framework Ge species. It should be noted that the Ir species in IrGe@S-1 might be partially reduced by H\u003csub\u003e2\u003c/sub\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC and quickly oxidized (~+4, \u003cstrong\u003eFig. 2a\u003c/strong\u003e) upon exposure to air. Nevertheless, the atom-level dispersion of Ir species could be well preserved during the whole process (\u003cstrong\u003eFig. 1\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eThe electronic states of Ir sites were further investigated by \u003cem\u003ein-situ\u003c/em\u003e FT-IR spectra of CO adsorption and \u003cem\u003equasi\u003c/em\u003e\u003cem\u003e\u0026nbsp;in-situ\u0026nbsp;\u003c/em\u003eXPS. As shown in \u003cstrong\u003eFig. 2d\u003c/strong\u003e, the intensity of CO adsorption band on Ir@S-1 is much higher than IrGe@S-1 because CO binds more tightly to the metallic site than to the oxidized M\u003csup\u003e\u0026delta;\u003c/sup\u003e\u003csup\u003e+\u003c/sup\u003e site (\u003cem\u003evide infra\u003c/em\u003e).\u003csup\u003e33\u003c/sup\u003e For Ir@S-1, the bands at 2,069 and 1,990 cm\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e are assigned to the symmetric and asymmetric stretching vibrations of well distributed Ir nanoclusters.\u003csup\u003e17,34\u003c/sup\u003e Due to the substitution of Ge, the \u003cem\u003e\u0026nu;\u003c/em\u003e(CO) frequency increases from 2069 to 2078 cm\u003csup\u003e-1\u003c/sup\u003e, attributed to the dicarbonyl species absorbed on positively charged Ir single atoms.\u003csup\u003e34,35\u003c/sup\u003e The enhanced interaction between Ir and framework oxygen atoms results in electron transfer from Ir to O and weakens the feedback \u0026pi; bond of Ir to CO. \u003cem\u003eQuasi\u003c/em\u003e\u003cem\u003e\u0026nbsp;in-situ\u003c/em\u003e XPS was then performed to further investigate the chemical state of the Ir species after high temperature reduction. The observed Ir 4f signal at 61.2 eV is assigned to mixed chemical states of Ir approaching to the metallic state with lots of highly dispersed Ir nanoclusters in Ir@S-1 (\u003cstrong\u003eFig. 2e\u003c/strong\u003e). In the case of IrGe@S-1, the signal of Ir 4f is observed at 61.8 eV, corresponding to the positively charged Ir\u003csup\u003e\u0026delta;\u003c/sup\u003e\u003csup\u003e+\u003c/sup\u003e sites anchored by framework oxygen atoms. These results confirm the uniform dispersion of Ir sites upon the introduction of Ge, and the Ir single atoms carry positive charges due to the enhanced electron transfer to framework oxygen with the presence of Ge. Upon exposure to air under ambient conditions, both metallic Ir clusters (Ir@S-1) and positively charged Ir\u003csup\u003e\u0026delta;\u003c/sup\u003e\u003csup\u003e+\u003c/sup\u003e sites (IrGe@S-1) are quickly transformed to the highly oxidized states (\u003cstrong\u003eFig. 2a\u003c/strong\u003e), and therefore, great caution should be taken to identify the real oxidation state of Ir sites in the samples.\u003c/p\u003e\n\u003cp\u003eThe interactions between Ir and O were explored by theoretical simulations. The effective Bader charge on Ir atom and the charge density difference resulting from Ir\u0026ndash;O interaction were computed. The Bader charge of an isolated Ir site is +0.80 |e|, corresponding to the electron-depletion region around Ir atoms (\u003cstrong\u003eFig. 2f\u003c/strong\u003e) and agreeing well with the experimentally observed Ir\u003csup\u003e\u0026delta;\u003c/sup\u003e\u003csup\u003e+\u003c/sup\u003e sites (\u003cstrong\u003eFig. 2e\u003c/strong\u003e). From partial density of states (pDOS) analyses, Ir\u0026ndash;O bonds are formed by the mixing of Ir s-d orbitals with O d orbitals (\u003cstrong\u003eFig. 2g-h\u003c/strong\u003e). In comparison, the hybridization with Ge 4p or 3d orbitals contribute less to the stabilization of Ir atoms (\u003cstrong\u003eFig. 2i\u003c/strong\u003e). Therefore, in combination with experimental and theoretical results, the Ir atoms are directly stabilized by framework oxygen atoms of MFI zeolite, and the enhanced overlapping between Ir 5d and O 2p in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI (four Ge atoms in the 4-MRs of MFI) model rationalizes the favorable \u0026Delta;E\u003csub\u003ef\u003c/sub\u003e of Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI. The Ir\u0026ndash;O bond strength was quantitively determined by crystal orbital Hamilton population (COHP) analysis (\u003cstrong\u003eSupplementary Figure 12\u003c/strong\u003e). The more negative integral COHP (ICOHP) value in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI reveals the stronger Ir\u0026ndash;O binding (\u003cstrong\u003eFig. 2j\u003c/strong\u003e). In addition, for various IrGe-MFI models, there is a positive relationship between ICOHP values and\u0026nbsp;\u0026Delta;E\u003csub\u003ef\u003c/sub\u003e, which once again validates that the Ir atom is efficiently stabilized by Ir\u0026ndash;O\u0026ndash;Ge bonds.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCatalytic performance in propylene dehydrogenation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe as-prepared catalysts were tested in PDH reaction with pure propane feeding under high WHSV of 20 h\u003csup\u003e-1\u003c/sup\u003e at 600 \u0026deg;C. As shown in \u003cstrong\u003eFig. 3a\u003c/strong\u003e, IrGe@S-1 shows distinctly higher activity in comparison with Ir@S-1 and Ge@S-1. To optimize the structure of active site in IrGe@S-1, a series of samples with varying initial Ge loadings of 0\u0026ndash;20 wt% were prepared and evaluated, with focuses on the specific activity and deactivation rate. As shown in \u003cstrong\u003eFig. 3b\u003c/strong\u003e, the specific activity of IrGe@S-1 is over two times higher than that of Ir@S-1 with the introduction only trace Ge in the synthesis gel (0.25 wt%). With increase in the initial loading of Ge in the synthesis gel (lower than 10 wt%),\u0026nbsp;the deactivation rate of catalyst decreases gradually. The introduction of excess Ge during the crystallization process will increase the number of defect sites and also change the zeolite morphology (\u003cstrong\u003eSupplementary Table 1\u003c/strong\u003e, \u003cstrong\u003eSupplementary Figure 13-14\u003c/strong\u003e). As a result, the deactivation rate of catalyst shows the trend of volcanic curve with lowest deactivation rate obtained at initial Ge loading of 10 wt% (1.43 wt% measured in IrGe@S-1 sample, \u003cstrong\u003eSupplementary Table 2\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eThe optimized IrGe@S-1 catalyst was tested in the long-term operation at 580 \u0026deg;C for 800 hours, showing very stable propane conversion of \u0026gt;30% with propylene selectivity of \u0026gt;97% (\u003cstrong\u003eFig. 3c\u003c/strong\u003e). It should be noted that a high WHSV of 20 h\u003csup\u003e-1\u003c/sup\u003e is employed in our durability test, several times higher that employed in industrial PDH process (UOP, WHSV: 4 h\u003csup\u003e-1\u003c/sup\u003e). Under such circumstance, about 9000 ton of propylene can be produced employing one ton of IrGe@S-1 catalyst without regeneration, which can satisfy the requirement of fixed-bed PDH process and is comparable with the most stable catalyst recently reported like RhIn@S-1\u003csup\u003e16\u003c/sup\u003e and PtSn@S-1\u003csup\u003e36\u003c/sup\u003e. The propylene space-time-yield (STY) value of IrGe@S-1 at 600 \u0026deg;C is calculated to be 1249 mol\u003csub\u003eC3H6\u003c/sub\u003e g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e h\u003csup\u003e-1\u003c/sup\u003e, an order of magnitude higher than the other catalysts reported in the literature (\u003cstrong\u003eSupplementary Table 4\u003c/strong\u003e), undoubtedly outperforming the state-of-the-art Pt-based catalysts (\u003cstrong\u003eFig. 3d\u003c/strong\u003e). On the other hand,\u0026nbsp;IrGe@S-1 is definitely better than other Ir-based zeolite catalysts in terms of both activity and stability (\u003cstrong\u003eSupplementary Figure 15\u003c/strong\u003e). To investigate the deactivation and regeneration properties of IrGe@S-1 catalyst, extremely harsh reaction conditions (600\u0026nbsp;\u0026deg;C, WHSV=300 h\u003csup\u003e-1\u003c/sup\u003e) were employed. As shown in \u003cstrong\u003eSupplementary Figure 16\u003c/strong\u003e, gradual declines in propane conversion could be observed with time-on-stream (propylene selectivity well preserved), indicating the deactivation of catalyst. Fortunately, the catalytic activity of IrGe@S-1 can be fully recovered \u003cem\u003evia\u003c/em\u003e simple calcination treatment, demonstrating its robustness for industrial applications. Moreover, IrGe@S-1 shows high activity in the dehydrogenation of ethane and n-butane, producing ethylene and butenes as the target products, respectively (\u003cstrong\u003eSupplementary Figure 17-18\u003c/strong\u003e). For the direct dehydrogenation of alkanes, the conversions of alkanes increase as the temperature increase from 450 to 600 \u0026deg;C, which is close to the thermodynamic equilibrium (\u003cstrong\u003eSupplementary Figure 19\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eThe spent IrGe@S-1 catalyst (after reaction at 600 \u0026deg;C for 18 h) was thoroughly characterized by TEM, thermogravimetry and XPS. As shown in \u003cstrong\u003eSupplementary Figure 20\u003c/strong\u003e, the atomic-level dispersion of Ir species is well maintained in the spent IrGe@S-1 catalyst while carbon deposition on the surface of zeolite is observed, which might inhibit the diffusion of the propane and trigger catalyst deactivation. In contrast, the average size of Ir species in Ir@S-1 grows up to ~6 nm after reaction and partial Ir particles escape from the channel of zeolite, resulting in irreversible catalyst deactivation (\u003cstrong\u003eSupplementary Figure 21\u003c/strong\u003e). The amounts of coke on IrGe@S-1 and Ir@S-1 catalyst after PDH reaction for 18 hours is determined to be 3.8 and 3.0 %, respectively, while the amount of coke on IrGe@S-1 after PDH reaction for 800 hours (at 580 \u003csup\u003eo\u003c/sup\u003eC) is reduced to 3.0 % (\u003cstrong\u003eSupplementary Figure 22\u003c/strong\u003e). These observations reveal that carbon deposition is rapid in the early stage of the reaction and the dynamic balance of coke deposition-digestion is important to achieve stable PDH reaction.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReaction mechanism of PDH over IrGe@S-1 catalyst\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eKinetic analyses of PDH catalyzed by IrGe@S-1 were performed with the elimination of diffusion resistance according to the Madon-Boudart criterion (\u003cstrong\u003eSupplementary Figure 23\u003c/strong\u003e).\u003csup\u003e37\u003c/sup\u003e The impacts of propane and H\u003csub\u003e2\u003c/sub\u003e partial pressure on the reaction rates at 460 \u0026deg;C are shown in \u003cstrong\u003eSupplementary Figure 24\u003c/strong\u003e. The fitting curves demonstrate a close to first-order dependence (0.79) on propane and a negative H\u003csub\u003e2\u003c/sub\u003e reaction order of -0.36.\u003csup\u003e38\u003c/sup\u003e It is therefore assumed that the first C\u0026ndash;H bond cleavage is the rate-limiting step while other steps are quasi-equilibrated.\u003csup\u003e39\u003c/sup\u003e The relation between reaction rate and propane partial pressure is given as \u003cstrong\u003eequation S11\u003c/strong\u003e in the supplementary information. The kinetic data were obtained at low conversions and fitted to get the rate constant for the first C\u0026ndash;H bond cleavage (k\u003csub\u003e2\u003c/sub\u003e) (\u003cstrong\u003eSupplementary Figure 25\u003c/strong\u003e). The apparent activation energy of the dehydrogenation rate coefficient (Ea) determined by Arrhenius plots is 41.5 kJ mol\u003csup\u003e-1\u003c/sup\u003e (\u003cstrong\u003eSupplementary Figure 26\u003c/strong\u003e), which appears to be distinctly lower than that reported for Pt-based catalysts reported, for example 56.2 kJ mol\u003csup\u003e-1\u003c/sup\u003e for PtFe\u003csub\u003e3\u003c/sub\u003e@S-1 and 67.4 kJ mol\u003csup\u003e-1\u003c/sup\u003e for PtZn-SPP.\u003csup\u003e40,41\u003c/sup\u003e That is, IrGe@S-1 should be an intrinsically better catalyst for the cleavage of first C\u0026ndash;H bond in propane molecules and it can catalyze the PDH reaction at very low reaction temperature of 300-400 \u0026deg;C, as shown in \u003cstrong\u003eSupplementary Table 5\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003ePropane temperature-programmed surface reaction (C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003e-TPSR) profiles reveal that the initial reaction temperature (T\u003csub\u003e0\u003c/sub\u003e), determined by the appearance of the H\u003csub\u003e2\u003c/sub\u003e signal, over IrGe@S-1 catalysts is slightly lower than that over Ir@S-1 (\u003cstrong\u003eSupplementary Figure 27\u003c/strong\u003e). According to the changes in the intensity of propylene signal, the introduction of Ge species promotes the catalytic performance\u0026nbsp;by an order of magnitude. On the other hand, the H\u003csub\u003e2\u003c/sub\u003e signal starts to decline and the CH\u003csub\u003e4\u003c/sub\u003e signal rises rapidly above 600 \u0026deg;C, indicating that the optimal operation temperature of IrGe@S-1 catalyst is below 600 \u0026deg;C.\u003c/p\u003e\n\u003cp\u003eFT-IR spectra of CO adsorption on IrGe@S-1 demonstrate a redshift in CO stretching frequency after reacting with propane (from 2078 to 2067 cm\u003csup\u003e-1\u003c/sup\u003e) (\u003cstrong\u003eFig. 4a\u003c/strong\u003e), indicating the enhanced electron donation from Ir atom to CO molecules and corresponding to the metallic electronic state of Ir species. The PDH mechanism over Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI model was then investigated using DFT calculations. As shown in \u003cstrong\u003eSupplementary Figure 28\u003c/strong\u003e, the energy barrier of the first and second dehydrogenation step on Ir site of Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI is 145.3 and 30.4 kJ mol\u003csup\u003e-1\u003c/sup\u003e. After releasing propylene molecules, the generated intermediates\u0026nbsp;*H are bound at the top site of the Ir atom and the oxygen atom with the formation of a hydroxyl group, respectively. These\u0026nbsp;*H intermediates exhibit a strong thermodynamic tendency to be released as H\u003csub\u003e2\u003c/sub\u003eO with breakage of one Ir\u0026ndash;O bond, in contrast to direct *H coupling (-57.4 \u003cem\u003eversus\u003c/em\u003e 85.2 kJ mol\u003csup\u003e-1\u003c/sup\u003e), thereby generating the oxygen-deficient Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e site. This is consistent with the dynamic transformation introducing localized electron density redistribution at the Ir center, as confirmed by charge density difference diagram in \u003cstrong\u003eSupplementary Figure 29\u003c/strong\u003e. As a result, metallic Ir site with Bader charge of \u0026ndash;0.19 |e| is generated in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e. The above dynamic evolution behavior of Ir\u003csub\u003e1\u003c/sub\u003e site is illustrated in \u003cstrong\u003eFig. 4b\u003c/strong\u003e. \u003cem\u003eIn-situ\u003c/em\u003e FT-IR spectra of propane dehydrogenation on IrGe@S-1 were recorded to monitor the formation of Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e site in IrGe@S-1 catalyst. As shown in \u003cstrong\u003eFig. 4c\u003c/strong\u003e, the intensity of band at 3720 cm\u003csup\u003e-1\u003c/sup\u003e increases distinctly after introducing propane due to the formation of hydroxyl groups. A series of bands between 3500-3800 cm\u003csup\u003e-1\u003c/sup\u003e are attributed to H\u003csub\u003e2\u003c/sub\u003eO molecules in the gas phase, the intensities of which increase at the initial stage and start to decrease after forming Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e sites (\u003cstrong\u003eSupplementary Figure 30\u003c/strong\u003e). Further calculations were conducted on the \u003cem\u003ein-situ\u003c/em\u003e formed Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e site. As shown in \u003cstrong\u003eFig. 4d\u003c/strong\u003e, this Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e site exhibits much better dehydrogenation reactivity with significantly lower energy barrier for the first C\u0026ndash;H cleavage (71.4 kJ mol\u003csup\u003e-1\u003c/sup\u003e) in comparison with pristine Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI (145.3 kJ mol\u003csup\u003e-1\u003c/sup\u003e), implying that Ir species in the approaching metallic state are more active for C\u0026ndash;H bond cleavage (\u003cstrong\u003eSupplementary Table 6\u003c/strong\u003e). The kinetic barrier of C\u0026ndash;H bond cleavage on Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e is also comparable as that on Ir (111) slab, \u003cem\u003ei.e.\u003c/em\u003e, simulating Ir nanoparticles, while there is an obvious difference in\u0026nbsp;*H coupling kinetics between them. Specifically, the\u0026nbsp;*H coupling step requires an energy value of 25.6 kJ mol\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003eon Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e site, which is much smaller than the value of 121.5 kJ mol\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003eon Ir (111) slab. In this sense, the fast\u0026nbsp;*H removal kinetics on Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e site contribute to the recovery of the active site for propane adsorption and reaction. The rate-degree control analysis was also performed for Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u0026nbsp;\u003c/sub\u003esite using the above DFT-calculated reaction energy data. The results suggest the propane C\u0026ndash;H bond cleavage as the rate-determining step at reaction temperature of 600 \u0026deg;C (\u003cstrong\u003eSupplementary Figure 31\u003c/strong\u003e), consistent with the experimental results. The propylene desorption energy values over the Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e and the Ir (111) slab were also calculated, as shown in \u003cstrong\u003eSupplementary Figure 32\u003c/strong\u003e. The desorption of propylene on Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e is thermodynamically favorable and the over-dehydrogenation of *C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003e requires to overcome an energy barrier of 237.3 kJ mol\u003csup\u003e-1\u003c/sup\u003e. In contrast, the over-dehydrogenation of\u0026nbsp;*C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003e is thermodynamically favorable than its desorption on Ir (111) site. Therefore, the side reaction of over-dehydrogenation on large Ir particles will reduce the selectivity toward target product propylene. Combining the kinetic experiments and theoretical calculation results, the first dehydrogenation step is the rate-determining step of PDH reaction and the \u003cem\u003ein-situ\u003c/em\u003e formed Ir single atoms in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e contribute to the superior PDH performance of IrGe@S-1 catalyst. The Ir single atoms in low oxidation states show significant selectivity in activating the C\u0026minus;H bond of propane, and are kept stable even under high temperature conditions.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003ePrevious studies have demonstrated that Ir single atom catalysts show potential in catalyzing alkane dehydrogenation, while the stability of Ir active sites should be significantly improved for working under harsh reaction conditions. The rational modification of Ir active sites might simultaneously enhance the intrinsic reactivity and the high-temperature stability. Herein, thermal stable Ir single atoms anchored by the zeolite framework oxygen atoms have been prepared \u003cem\u003evia\u003c/em\u003e a one-pot route, showing superior thermal stability without any metal sintering during high-temperature reduction and dehydrogenation process (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cb\u003eSupplementary Fig.\u0026nbsp;20\u003c/b\u003e). The improved stability is attributed to the incorporation of Ge species into MFI framework at the [4\u003csup\u003e1\u003c/sup\u003e5\u003csup\u003e2\u003c/sup\u003e6\u003csup\u003e2\u003c/sup\u003e] cages and the overlap between Ir 5d and O 2p orbital by forming Ir–O–Ge bonds (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The integral COHP (ICOHP) value in Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI further confirms the stronger Ir–O binding with increasing Ge atoms in 4-MRs (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej). Experimentally, IrGe@S-1 exhibits an unprecedent propylene formation rate of 1249.2 mol\u003csub\u003eC3H6\u003c/sub\u003e g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e−1\u003c/sup\u003e h\u003csup\u003e− 1\u003c/sup\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC and perfect stability for at least 800 hours in PDH reaction (WHSV = 20 h\u003csup\u003e− 1\u003c/sup\u003e, 580 \u003csup\u003eo\u003c/sup\u003eC). Upon reaction with propane, one framework oxygen in IrGe@S-1 is removed as molecule H\u003csub\u003e2\u003c/sub\u003eO and an isolated Ir site in low oxidation state is formed, namely Ir\u003csub\u003e1\u003c/sub\u003e-Ge\u003csub\u003e4\u003c/sub\u003e-MFI-O\u003csub\u003evac\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The metallic nature of Ir species reduces the energy barrier of the first dehydrogenation step and the isolated nature of Ir sites restricts the over-dehydrogenation reaction, thereby breaking the scaling relationship between activity and selectivity in PDH reaction. This study provides a new perspective to manipulate the interaction of metal and support, showing promise for ultra-stable PDH with SACs.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cb\u003eMaterials\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTetrapropylammonium hydroxide solution (TPAOH, 40 wt% in H\u003csub\u003e2\u003c/sub\u003eO, J\u0026amp;K Scientific Ltd), tetraethyl orthosilicate (TEOS, 99.99% metals basis, Aladdin), hexachloroiridium acid hydrate (H\u003csub\u003e2\u003c/sub\u003eIrCl\u003csub\u003e6\u003c/sub\u003e·xH\u003csub\u003e2\u003c/sub\u003eO, Ir \u0026gt; 36%, Aladdin), dioxogermane (GeO\u003csub\u003e2\u003c/sub\u003e, 99.99% metals basis, Aladdin) and ethylenediamin (EDA, \u0026gt; 98%, Aladdin).\u003c/p\u003e\u003cp\u003e\u003cb\u003ePreparation of Ir@S-1\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe synthesis of S-1 zeolite encapsulated monometallic Ir sample (Ir@S-1) was realized by a one-pot method under hydrothermal conditions. The composition of the mixing gel was as follows: 1 SiO\u003csub\u003e2\u003c/sub\u003e: 0.4 TPAOH: 35 H\u003csub\u003e2\u003c/sub\u003eO: 0.0014 H\u003csub\u003e2\u003c/sub\u003eIrCl\u003csub\u003e6\u003c/sub\u003e (molar ratio). Typically, a mixture of TPAOH solution (13 g) and deionized water (15.4 g) was added to a 100 mL round bottom flask, and the homogeneous solution was obtained after 10 minutes of stirring. Subsequently, 8.32 g of TEOS were added dropwise to the mixture, which was then stirred continuously for 6 hours in order to form the desired gel. The metal precursor solution was prepared with H\u003csub\u003e2\u003c/sub\u003eIrCl\u003csub\u003e6\u003c/sub\u003e·xH\u003csub\u003e2\u003c/sub\u003eO and EDA with a molar ratio of 1:10. The prepared metal solution was then added to the mixing gel and stirred for additional 2 hours. Finally, the gel was transferred to a 100 mL Teflon-lined stainless steel autoclave and crystallized at 170°C for 72 hours. The Ir@S-1 sample was obtained after washing for three times and drying at 80°C for 12 hours.\u003c/p\u003e\u003cp\u003e\u003cb\u003ePreparation of IrGe@S-1\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe IrGe@S-1 catalysts were prepared by the same method as Ir@S-1. The molar ratio of the mixed gel was 1 SiO\u003csub\u003e2\u003c/sub\u003e: 0.4 TPAOH: 35 H\u003csub\u003e2\u003c/sub\u003eO: 0.0014 H\u003csub\u003e2\u003c/sub\u003eIrCl\u003csub\u003e6\u003c/sub\u003e: x Ge (x ranges from 0 to 0.12) and the as-prepared catalysts were denoted as IrxGe@S-1 (x represents the mass percent of Ge in the feed gel). Firstly, TPAOH solution (13 g) and deionized water (15.4 g) were mixed into a 100 mL round-bottom flask and stirred for 10 minutes. Secondly, TEOs (8.32 g) were added drop by drop while stirring and continued for another 6 hours. The metal precursor solution was prepared with H\u003csub\u003e2\u003c/sub\u003eIrCl\u003csub\u003e6\u003c/sub\u003e·xH\u003csub\u003e2\u003c/sub\u003eO and EDA, with a molar ratio of 1:10. A quantity of GeO\u003csub\u003e2\u003c/sub\u003e and the prepared metal solution was added to the mixing gel and stirred for a further 2 hours. Finally, the gel was transferred to a 100 mL Teflon-lined stainless steel autoclave and crystallized at 170°C for 72 hours. Following this, the IrGe@S-1 samples were obtained after washing for three times, drying (80°C for 12 hours) and reducing (600°C, 10% H\u003csub\u003e2\u003c/sub\u003e/Ar, 2 h).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003cstrong\u003es\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank the National Natural Science Foundation of China (22025802, 22025203, 22308257) for financial support. Shaojia Song thanks the financial support from the Open Project of Key Laboratory of Green Chemical Engineering Process of Ministry of Education (GCP2024005). We thank the staff members of BL17B beamline (https://cstr.cn/31129.02.NFPS.BL17B) at the National Facility for Protein Science in Shanghai (https://cstr.cn/31129.02.NFPS), for technical support in XAFS data collection and analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eG.L. contributed to conceptualization, investigation, resources, supervision, project administration, writing \u0026ndash; review and editing. M.S. contributed to investigation, methodology, data curation,\u0026nbsp;formal analysis, writing \u0026ndash; original draft\u0026nbsp;and review. S.S.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003econtributed to theoretical calculations, writing \u0026ndash; review and editing. G.H. contributed to investigation, methodology, data curation. W.L. contributed to data curation,\u0026nbsp;formal analysis. X.L. contributed to methodology, data curation,\u0026nbsp;formal analysis. J.L. contributed to supervision, writing \u0026ndash; review and editing. C.Y. contributed to investigation, methodology, formal analysis. S.F. contributed to investigation, methodology. R.W. contributed to investigation, data curation. B.Z. contributed to conceptualization, investigation, supervision,\u0026nbsp;writing \u0026ndash; review and editing. L.L. contributed to supervision, data curation,\u0026nbsp;writing \u0026ndash; review and editing.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026sect;\u003c/sup\u003e\u003csup\u003e\u0026nbsp;\u003c/sup\u003eMingxia Song and Shaojia Song contribute equally to this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ei\u003c/strong\u003e\u003cstrong\u003enterest\u003c/strong\u003e\u003cstrong\u003es\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data presented here are available with the paper or from the corresponding authors. Source data are provided with this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe detailed characterizations and experiments data are available in supplementary information (DOC).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding Author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGuozhu Liu\u003c/strong\u003e- Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China. Haihe Laboratory of Sustainable Chemical Transformations, Tianjin 300192, China.\u003c/p\u003e\n\u003cp\u003eEmail: [email protected]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLandong Li\u003c/strong\u003e-\u0026nbsp;Key Laboratory of Advanced Energy Materials Chemistry of Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071, P.R. China\u003c/p\u003e\n\u003cp\u003eEmail:\u0026nbsp;[email protected]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBofeng Zhang\u003c/strong\u003e- Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.\u003c/p\u003e\n\u003cp\u003eEmail: [email protected]\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eQiao, B.\u003cem\u003e et al.\u003c/em\u003e Single-atom catalysis of CO oxidation using Pt\u003csub\u003e1\u003c/sub\u003e/FeO\u003csub\u003ex\u003c/sub\u003e. \u003cem\u003eNat. 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However, the applications of single atom precious metal catalysts under harsh reaction conditions are significantly restricted due to thermodynamic instability from sintering-driven degradation. We report herein the construction of thermal stable Ir single atoms encapsulated in Ge-substituted S-1 zeolite, namely IrGe@S-1 catalysts, for direct propane dehydrogenation. The optimized IrGe@S-1 catalyst exhibits unprecedent propane dehydrogenation activity with a state-of-the-art propylene formation rate of 1249.2 mol\u003csub\u003eC3H6 \u003c/sub\u003eg\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e-1 \u003c/sup\u003eh\u003csup\u003e-1\u003c/sup\u003e at 600 \u003csup\u003eo\u003c/sup\u003eC. It also shows excellent stability for over 800 hours under a high weight hourly space velocity of 20 h\u003csup\u003e-1\u003c/sup\u003e (pure propane feeding at 580 \u003csup\u003eo\u003c/sup\u003eC), producing 9000 ton of propylene with one ton of IrGe@S-1 catalyst without regeneration. The introduction of Ge species promotes the overlap between Ir 5d and O 2p orbital and thereby enhances their interaction \u003cem\u003evia\u003c/em\u003e Ir–O–Ge bonds to derive Ir single atom catalysts. Under propane dehydrogenation conditions, propane molecules can induce the dissociation of framework oxygen atoms and the formation of Ir single atoms in low oxidation state. The specific electron-rich Ir single atoms significantly lower the energy barrier of the rate-determining step in propane dehydrogenation and the isolated nature of Ir sites efficiently inhibits the side reaction of over-dehydrogenation, together contributing to the remarkable performance in propane dehydrogenation. This work provides a successful example of stable single atom precious metal catalysts for working under harsh reaction conditions.\u003c/p\u003e","manuscriptTitle":"Zeolite-encapsulated Ir Single Atom Catalysts toward Efficient and Stable Propane Dehydrogenation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-28 06:04:51","doi":"10.21203/rs.3.rs-6912388/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"43e9ada7-0f02-437b-80df-deeb383989e0","owner":[],"postedDate":"July 28th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":51857473,"name":"Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis"},{"id":51857474,"name":"Physical sciences/Chemistry/Catalysis/Catalytic mechanisms"},{"id":51857475,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Structural properties"}],"tags":[],"updatedAt":"2025-07-28T06:04:51+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-28 06:04:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6912388","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6912388","identity":"rs-6912388","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}