Synthesis and Catalytic Oxidation Studies of a Novel Keggin-Type Complex Catalyst [(CH2)5NH2]5PMo10V2O40

Synthesis and Catalytic Oxidation Studies of a Novel Keggin-Type Complex Catalyst [(CH2)5NH2]5PMo10V2O40 | 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 Research Article Synthesis and Catalytic Oxidation Studies of a Novel Keggin-Type Complex Catalyst [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 Shi Jinyi, Ding Yuansheng This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8984427/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Developing efficient and robust polyoxometalate catalysts is highly desirable for green organic oxidation. In this work, we synthesized a novel organic-inorganic hybrid Keggin-type complex, [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 , via the assembly of phosphomolybdovanadic acid and piperidine. Structural analyses using FT-IR and XRD confirmed that the parent [PMo 10 V 2 O 40 ] 5− framework remains fully intact. Meanwhile, the intercalation of piperidinium cations expands the crystal lattice and induces a unique monoclinic supramolecular architecture. Thermogravimetric analysis revealed a significant enhancement in thermal stability, with the material resisting decomposition up to 433°C. We evaluated the practical utility of this complex in the selective oxidation of benzaldehyde to benzoic acid using aqueous H 2 O 2 . Under mild optimized conditions (75°C, 2.5 h), the catalyst achieved an 87% yield with absolute selectivity. This exceptional performance originates from two distinct structural advantages. The V/Mo heterometallic interaction inherently boosts the overall redox capacity, facilitating rapid oxidant activation. Concurrently, the organic cations construct a localized hydrophobic microenvironment within the lattice. This specific pocket selectively adsorbs the organic substrate and repels excess hydrophilic oxidants, thereby accelerating the reaction while effectively suppressing overoxidation. piperidinium phosphomolybdovanadate Keggin polyoxometalate Catalysis Benzoic acid Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction heteropolyacids and their salts constitute a class of polyoxygen cluster metal complexes featuring spatial arrangements where the central atom (e.g. P, Si) and the coordinating atoms (polyatomic, e.g. Mo, W) are bridged by oxygen atoms[1]. They exhibit well-defined dimensions, shapes, and structures resembling discrete fragments of metal oxides. They play an increasingly vital role in fields such as catalysis[2, 3], photochemistry[4], medicine[5, 6], materials science[7, 8], and magnetism[9], attracting significant attention. As catalysts, heteropolyacids and their salts offer environmental friendliness, high catalytic activity, excellent selectivity, rapid reaction rates, mild reaction conditions, oxidative activity, optical and magnetic properties, along with superior stability and minimal equipment corrosion[2, 7, 8, 10]. They can function in both homogeneous and heterogeneous reactions, even as phase-transfer catalysts. As dual-functional green catalysts combining acidic and redox properties, they hold significant application potential. Conducting innovative research with substantial application potential in the field of green chemistry, particularly investigating the use of polyoxometalates as green catalysts in organic synthesis (such as alkylation and dealkylation of aromatics, esterification, dehydration/condensation, redox reactions, ring-opening, condensation, addition, and etherification reactions), holds immense significance. Therefore, synthesizing novel, highly efficient multimetallic oxoacid catalysts has become a hot topic. This study reports the first synthesis of a Keggin-type complex [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 as a polymetallic oxo-acid catalyst. The synthesized catalyst was characterized, and a systematic investigation of various factors influencing its catalytic performance in the oxidation of benzaldehyde to benzoic acid yielded promising results. 1 Experimental 1.1 Main Reagents and Instruments Na 2 MoO 4 , hexahydropyridine, and benzaldehyde (analytical grade, Shanghai Reagent Factory); H 2 O 2( 30%), NaH 3 PO 4 (analytical grade, Beijing Chemical Plant); Magna560 Fourier Transform Infrared Spectrometer (KBr pressing pellets, recording range 400–4000 cm − 1 ; Nicolet Instruments, USA); Dmax 2200PC X-ray Powder Diffractometer (Rigaku Corporation, Japan); X-4 Digital Display Micro-Melting Point Apparatus (Beijing Tek Co., Ltd, China).; CT6-015 Thermal Analyzer (PerkinElmer, USA). 1.2 Synthesis of the Parent Acid H 5 PMo 10 V 2 O 40 ·nH₂O Weigh 8.13g of NaVO 3 , and dissolve in 37 mL of hot distilled water. Dissolve 2.36 g of NaH 3 PO 4 in 20 mL of hot distilled water. Combine both solutions and reflux under stirring at 90°C for 90 min, then cool to room temperature. Slowly add approximately 2 ml concentrated sulfuric acid, controlling pH ≈ 2. The solution changes from clear and transparent to dark red. Dissolve 40.3g Na 2 MoO 4 in 67 mL distilled water and add to the above solution. React for 30 min. Slowly add 28 ml concentrated sulfuric acid while stirring vigorously. After complete addition, react for 2 hours. During this process, the solution color gradually lightens, eventually becoming bright red. Add 100 ml of diethyl ether, shake vigorously, and allow to stand until layers separate. Collect the middle ether layer. Evaporate and concentrate in a fume hood over a 60°C water bath until a crystalline film forms on the liquid surface. Cool and allow the ether to evaporate completely to obtain bright red, transparent H 5 PMo 10 V 2 O 40 crystals. Recrystallize the crystals from the crude product using a mass ratio of approximately 1:1.2 (crystal: water). 1.3 Preparation and Crystal Growth of [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 Dissolve a certain amount of H 5 PMo 10 V 2 O 40 ·nH₂O in water to form a red transparent solution. Take a specific molar amount of hexahydropyridine and slowly add it to the red transparent solution under stirring. React at 70°C for 2 hours to produce a yellow-green precipitate. Filter the mixture. Wash the filter cake alternately with ethanol, diethyl ether, and water. After thorough washing, dissolve the cake in a proportionate mixture of acetonitrile and water. Filter again using quantitative filter paper to obtain a yellow-green transparent solution. Transfer the solution to a beaker, seal it with plastic wrap, and pierce the wrap with a needle to create uniform small holes. Allow the solution to slowly evaporate at room temperature in a well-ventilated, cool location. After approximately one week, yellow-green transparent crystals precipitated at the bottom of the beaker, identified as [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 crystals. 1.4 Catalytic Activity Experiment Weigh equal masses of [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 catalyst and H 2 O 2 (30%) were added to a 100 mL round-bottom flask. Under magnetic stirring, a certain amount of benzaldehyde was added dropwise, the temperature was raised to 75°C, and the reaction was carried out for 2.5 hours. The product was refrigerated for 24 hours. Filter and wash with saturated benzoic acid solution (to minimize loss), yielding white benzoic acid crystals. Dry the crystals, weigh them, and calculate the yield (mass fraction). Determine the melting point of the obtained product using a digital melting point apparatus. 2 Results and Discussion 2.1 Structural Characterization of the Catalyst 2.1.1 IR Spectroscopy Analysis of the Catalyst The IR results indicate that the polyoxometalate charge-transfer complex [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 exhibits four characteristic absorption peaks corresponding to the parent heteropolyacid anion [PMo 10 V 2 O 40 ] 5− . The P-Oa, Mo-Od, Mo-Ob-Mo, and Mo-Oc-Mo bond vibration peaks are at 1060.9, 962.1, 864.5, and 775.2 cm − 1 relative to the parent acid[ 11 , 12 ]. In the newly synthesized polyoxometalate piperidine charge-transfer complex, these four characteristic absorption peaks are 1060.2, 957.5, 864.7, and 790.8 cm − 1 . The region between 700 and 1100 cm⁻¹ represents the fingerprint absorption zone for polyanionic species. Comparison reveals that the newly synthesized charge-transfer complexes retain the Keggin structure of the polyanionic species, but the Mo-Ob-Mo and Mo-Oc-Mo absorption peaks exhibit a certain degree of blue shift, while the P-Oa and Mo-Od absorption peaks show a slight red shift. This occurs because in the newly synthesized polyoxometalate piperidine charge-transfer complexes, the charge from the protonated hexahydro-pyridine transfers to the polyoxometalate anion, exerting differential effects on various chemical bonds. This alters bond strengths, leading to red or blue shifts in absorption peaks. The absorption peaks of the polyoxometalate piperidine charge-transfer complexes in the wavenumber range of 1100–1500 cm⁻¹ correspond to the skeletal vibrations of the hexahydropyridine ring. Absorption vibrations above 3000 cm⁻¹ originate from the stretching vibrations of C-H and N-H bonds in the hexahydropyridine structure. The presence of these absorption peaks indicates the existence of the hexahydropyridine moiety. These results suggest a strong charge transfer interaction between the polyanion and the counterion, leading to the formation of the polyoxometalate piperidine charge transfer complex. 2.1.2 XRD Analysis of the Catalyst The XRD results show that the synthesized [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 has four strong diffraction peaks at 2θvalues of 10.32°, 22.58°, 24.98°, and 30.92°. The positions and relative intensity of these peaks are very similar to the standard patterns of the Keggin-type heteropoly acid (NH 4 ) 3 PMo 12 O 40 found in the library[ 3 ]. Also, comparing it with the cif file data for H 5 (PMo 10 V 2 O 40 )·36H 2 O shows that both crystals display the typical diffraction patterns of Keggin-type salts in the 5°–40° (2θ) range[ 11 ]. Specifically, the strongest peak below 10° belongs to the (110) plane, which is a clear sign that the Keggin anions are stacked along the c -axis. In addition, there are groups of medium-intensity peaks in the 15°–25° and 28°–35° ranges. These peaks come from the complex atomic structure inside the [PMo 10 V 2 O 40 ] 5- anion. However, there is a clear difference: all main peaks of [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 are shifted to lower angles compared to H 5 (PMo 10 V 2 O 40 )·36H 2 O. For example, the (110) peak moves from 9.7° to about 7.9°. According to Bragg’s Law, this shift means the interplanar spacing increases from 9.1 Å to 11.2 Å. This suggests that the large [(CH 2 ) 5 NH 2 ] + cations (about 6–7 Å in diameter) have filled the gaps between the Keggin anions, causing the crystal unit cell to expand slightly. This expansion is direct evidence from XRD that the organic molecules have successfully entered the inorganic structure. In addition, the peak intensities changed significantly. The peak near 22.0°, which belongs to planes like (222), is much stronger in the hybrid crystal. Since peak intensity depends on the type and position of atoms in the cell, this change reflects a difference in electron density. The organic cations have carbon and nitrogen atoms that are rich in electrons, replacing the water/protons (which have light atoms like H and O). This introduces new strong scattering centers, changing the overall electron density of the crystal. Finally, adding the large and oriented organic amine cations significantly reduces the crystal symmetry. The crystal structure changes from the high-symmetry tetragonal system (P4/mnc) of H 5 (PMo 10 V 2 O 40 )·36H 2 O to the monoclinic system (P2 1 /c) of [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 . Due to the size and directional hydrogen bonds of the organic cations, the unit cell becomes distorted, so the axis lengths are no longer equal and the β angle is not 90°. This structural change is seen in the XRD results as a clear increase in the number of peaks and peak splitting, especially at low angles. As the symmetry becomes lower, the Mo/V atoms are more likely to be distributed in different positions, increasing the local structural differences[ 13 , 14 ]. 2.1.3 TG Analysis of Catalysts Analysis of the thermogravimetric (TG) curve reveals that the weight loss of the polyoxometalate piperidine charge-transfer complex [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 occurs in three distinct stages. The first stage, spanning 199.04°C to 257.68°C, involves the loss of bound water molecules hydrogen-bonded to acidic protons, accounting for 1.215% of the total weight loss. The second stage, from 264.60°C to 433.36°C, involves weight loss from the cation of the polyoxometalate piperidine charge-transfer complex, accounting for 16.363% of the total weight loss; The third stage occurs from 693.20°C to 800°C, during which the anion undergoes complete decomposition with a weight loss of 27.603%. At this point, the polyoxometalate piperidine charge-transfer complex transforms into Mo 2 O 3 and V 2 O 3 . The curve indicates that the decomposition temperature of this polyoxometalate piperidine charge-transfer complex is 433°C, whereas the theoretical decomposition temperature of its parent acid H 5 PMo 10 V 2 O 40 is 375°C[ 15 ]. The enhanced thermal stability of this crystal structure primarily stems from the hybridization of organic molecules with the parent acid. Here, the piperidine cation acts as a “molecular pillar,” filling the interstitial spaces of the Keggin anion. This not only prevents the framework from collapsing under reaction conditions but also inhibits the leaching and loss of active components through steric hindrance effects. This structure not only elevates the catalyst's thermal stability by approximately 60°C but also significantly enhances its tolerance to high concentrations of hydrogen peroxide (30% H 2 O 2 ). Based on the above data, the molecular structure of the new compound can be established as [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 . Therefore, we employed MS software modeling to obtain the schematic 3D crystal structure of [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 , as shown in Fig. 4 . The crystal structure of [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 exhibits the characteristic hybridization of an “inorganic framework-organic cation” assembly. The overall unit cell belongs to the monoclinic system with space group P 2 1 / c . The inorganic framework core consists of a classic Keggin-type heteroanion [PMo 10 V 2 O 40 ] 5− , which possesses a symmetrical cage structure. A phosphorus-oxygen tetrahedron (PO 4 ) occupies the central position, tightly enclosed by ten molybdenum-oxygen octahedra (MoO 6 ) and two vanadium-oxygen octahedra (VO 6 ). These octahedra connect via shared oxygen vertices, forming a nearly spherical, rigid nanocluster. Two vanadium atoms (V 5+ ) occupy positions originally intended for molybdenum in a disordered manner, preferring symmetry-related coordination sites. This coexistence of V and Mo generates V-O-Mo heterometallic bridges within the anion framework, introducing localized electron asymmetry and abundant redox active sites. Five positively charged piperidine cations[(CH 2 ) 5 NH 2 ] + cations with the negatively charged inorganic anionic framework through strong electrostatic interactions. Each pyridine ring (a five-membered saturated nitrogen-containing heterocycle) adopts a lower-energy chair conformation, with its -NH 2 + end interacting via hydrogen bonds and ionic bonds with oxygen atoms on the anion surface. This forms a spatial crystal structure characterized by a rigid anionic framework and flexible cationic fillers. The use of heteropolyacids as catalysts has long been one of their most significant applications. The crystal phase [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 exhibits structural differences compared to traditional Keggin-type heteropolyacids, and these differences inevitably influence its catalytic performance. At the electronic structure level, the partial substitution of Mo by V generates heterometallic synergy effects. In the conventional PMo 12 structure, redox processes primarily rely on the Mo 6+ /Mo 5+ electron pair, which possesses relatively limited reduction potential. In contrast, the PMo 10 V 2 structure creates an electron-asymmetric environment where V 5+ interacts with Mo 6+ . The V = O bond is shorter and stronger than the Mo = O bond, endowing the V 5+ /V 4+ redox pair with a higher reduction potential. This modification lowers the activation energy barrier for hydrogen peroxide activation while providing more flexible electron transfer pathways, significantly enhancing the catalyst's oxidation capacity. More importantly, the introduction of piperidine cations enables precise regulation of the catalytic microenvironment. Traditional H-type Keggin acids, while highly acidic, often exhibit strong Brønsted acidity that promotes side reactions and are prone to dissolution and loss in aqueous solutions. In this catalyst, five [(CH 2 ) 5 NH 2 ] + cations form hydrophobic channels of specific dimensions within the crystal lattice. This microenvironment exhibits preferential adsorption for certain organic molecules (e.g., benzaldehyde) while repelling the more hydrophilic hydrogen peroxide. This microenvironment preferentially adsorbs certain organic molecules (e.g., benzaldehyde) while moderately repelling more hydrophilic hydrogen peroxide and reaction intermediates. This facilitates in situ enrichment of substrates and timely desorption of products, effectively preventing the overoxidation of benzoic acid. Simultaneously, the piperidine cation weakens the catalyst's strong protonic acidity while enhancing its Lewis acidity characteristics. This allows the V 5+ sites to coordinate more selectively with specific functional groups (e.g., carbonyl oxygen), thereby improving the catalyst's selectivity. To evaluate the catalytic performance of the crystalline [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 , a classic chemical reaction was employed;the oxidation of benzaldehyde to benzoic acid catalyzed by polyoxometalates using H 2 O 2 . The experimental results are as follows. 2.2 Catalytic Activity Experiments 2.2.1 Effect of Reaction Time on Yield Using [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 as the catalyst, the effect of reaction time on catalytic activity was investigated under constant conditions, with results shown in Fig. 5 (a). Figure 5 (a) indicates that the yield gradually increases as the reaction time extends from 1.5 h to 2.5 h. Beyond this point, further increases in reaction time yield no change in the reaction yield, which remains essentially constant by 3.5 h. Therefore, the optimal reaction time is determined to be 2.5 hours. 2.2.2 Effect of Catalyst Dosage on Yield Using [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 as the catalyst, the effect of catalyst dosage on catalytic activity was investigated under constant conditions, with results shown in Fig. 5 (b). Figure 5 (b) indicates that when the molar ratio of catalyst to benzaldehyde exceeds 1.89×10 − 4 , the yield increases with rising molar ratio. between 1.89×10 − 4 and 2.84×10 − 4 , the increase exhibits linear growth with the most significant and pronounced magnitude. At this point, the effective utilization rate of hydrogen peroxide is significantly influenced by the catalyst dosage. When the molar ratio exceeds2.84×10 − 4 , the benzoic acid yield essentially remains constant. Therefore, the optimal molar ratio of the catalyst [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 to benzaldehyde is 2.84×10 − 4 . 2.2.3 Effect of Hydrogen Peroxide on Yield Using [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 as the catalyst, the effect of H 2 O 2 dosage on catalytic activity was investigated under constant conditions, with results shown in Fig. 5 (c). Figure 5 (c) indicates that upon addition of H 2 O 2 , the benzoic acid yield increases with rising H 2 O 2 dosage, reaching a maximum at a molar ratio of H 2 O 2 to benzaldehyde of 3.53:1. However, as the H 2 O 2 amount further increased, the benzoic acid yield slightly decreased. This indicates that excessive H 2 O 2 is detrimental to this oxidation reaction. This may occur because, at the reaction temperature, an excess of H 2 O 2 can cause a small portion of the benzoic acid to form its peroxide. Therefore, the optimal molar ratio of H 2 O 2 to benzaldehyde is 3.53:1. 2.2.4 Effect of Temperature on Yield Using [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 as the catalyst, the effect of reaction temperature on catalytic activity was investigated while other conditions remained constant. The results are shown in Fig. 5 (d). Figure 5 (d) indicates that when the temperature exceeds 65°C, the reaction becomes significantly affected by temperature. The highest yield was achieved at 75°C. Further increasing the temperature beyond 75°C did not alter the reaction yield. Therefore, the optimal reaction temperature is determined to be 75°C. 2.2.5 Blank Experiment In this oxidation reaction, without adding a catalyst and keeping other conditions unchanged, the yield of benzoic acid is only about 27.5% when the optimal amount of 30% H 2 O 2 is added. Moreover, the product exhibits a pale yellow color and a melting point ranging from 115.1°C to 119.1°C, with a significantly lower yield compared to the reaction without a catalyst. This demonstrates that the catalyst accelerates the oxidation reaction process, leading to a substantial increase in benzoic acid yield. If 30% H 2 O 2 is omitted and the optimal amount of catalyst is added while maintaining other conditions constant, no benzoic acid is formed. This indicates that the catalyst does not possess oxidative functionality but instead catalyzes the oxidation reaction. 2.2.6 Verification Experiment To verify the reliability of the optimal conditions determined in the experiments, three parallel experiments were conducted. The results are shown in Table 1 . Table 1 Experimental Reaction Conditions (Verification Experiments) No. n benzaldehyde :nH 2 O 2 Reaction Temperature/°C n Catalyst : n Benzaldehyde /×10⁻⁴ Reaction Time/h Yield/% 1 1:3.53 7.5 2.84 2.5 87.03 2 1:3.53 7.5 2.84 2.5 87.15 3 1:3.53 7.5 2.84 2.5 86.87 The experimental data in Table 1 indicate that the optimal reaction conditions are: reaction temperature of 75°C; molar ratio of hydrogen peroxide to benzaldehyde of 3.53:1; molar ratio of catalyst to benzaldehyde of 2.84×10 − 4 :1; reaction time of 2.5 hours; and yield exceeding 85%. The results above demonstrate that [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 significantly enhances the catalytic efficiency of traditional Keggin catalysts through a dual strategy of V/Mo heterometallic synergy and organic cation microenvironment regulation. This organic-inorganic catalyst design concept offers a novel approach for developing highly efficient, stable, and selective polyacid-based oxidation catalysts, presenting broad application prospects. 3 Conclusions This study successfully designed and synthesized a novel organic-inorganic hybrid material [(CH 2 ) 5 NH 2 ] 5 PMo 10 V 2 O 40 . IR and XRD structural analyses confirm that this material fully inherits the framework structure of the Keggin-type [PMo 10 V 2 O 40 ] 5− anion. Simultaneously, the ordered incorporation of the [(CH 2 ) 5 NH 2 ] + cation induces lattice expansion, redistribution of electron density, and enhanced long-range order, forming a unique supramolecular assembly. In the selective oxidation of benzaldehyde to benzoic acid, this catalyst demonstrates outstanding comprehensive performance; achieving 86% conversion and 100% selectivity under mild conditions, significantly outperforming conventional Keggin catalysts. Its outstanding performance stems from the ingenious combination of V/Mo heterometallic synergistic enhancement of redox capabilities and the hydrophobic microenvironment constructed by the piperidine cation; the former lowers the reaction energy barrier and accelerates H 2 O 2 activation; the latter enriches organic substrates and promotes product desorption, thereby simultaneously enhancing catalytic activity, selectivity, and stability. Declarations Funding The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author contributions All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by S. J. and D. Y.. The first draft of the manuscript was written by S. J., and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Data availability All data generated or analyzed during this study are included in this published article. Ethics approval Not applicable. This study does not involve human participants or animals. Consent to participate Not applicable. Consent for publication Not applicable. References Hill, C.L., Introduction: Polyoxometalates . Chemical Reviews, 1998. 98(1): p. 1–2. Hill, C.L., Preface: Polyoxometalates in catalysis . Journal of Molecular Catalysis A: Chemical, 2007. 262(1–2): p. 1–2. Paul, S., H. Hu, and M. Abon, Structural Evolution under Reaction Conditions of Supported (NH4)3HPMo11VO40 Catalysts for the Selective Oxidation of Isobutane . Catalysts, 2015. 5(1): p. 461–479. Zhang, L., et al., A new heterogeneous photocatalyst based on Wells–Dawson polyoxometalate and nickel coordination compounds: synthesis, structure and property . Research on Chemical Intermediates, 2015. 41(3): p. 1691–1702. Rhule, J.T., et al., Polyoxometalates in Medicine . Chemical Reviews, 1998. 98(1): p. 327–358. Ghosh, S.K., R. Saha, and B. Saha, Toxicity of inorganic vanadium compounds . Research on Chemical Intermediates, 2015. 41(7): p. 4873–4897. Rao, A.S., et al., Polyoxometalates: Toward new materials . Journal of Chemical Sciences, 2011. 123(2): p. 229–239. Zhang, Y., et al., Recent advances in polyoxometalate-based materials and their derivatives for electrocatalysis and energy storage . Materials Chemistry Frontiers, 2024. 8(3): p. 732–768. Sahu, P.K., S. Kapurwan, and S. Konar, Epitome of polyoxotungstate-coordinated lanthanide-based single-molecule magnets. Chemical Communications, 2025. Li, H., et al., Deep Oxidative Desulfurization of Fuels Catalyzed by Ionic Liquid-Type Phosphomolybdates . Energy & Fuels, 2009. 23(3): p. 1354–1359. Li, Y., S. Li, and Y. Kong, Hydroxylation of benzene to phenol over heteropoly acid H5PMo10V2O40 supported on amine-functionalized MCM-41 . RSC Advances, 2021. 11(43): p. 26571–26580. Fournier, M., et al., Vanadium-substituted 12-molybdophosphoric acids: Syntheses, stability and characterization of the pure 1, 2 and 3 vanadium species . Journal of Materials Chemistry, 1992. 2(9): p. 971–978. Scalerandi, G.S., F.E. Tuler, and L.R. Pizzio, Tetrabutyl Ammonium Salts of Keggin-Type Vanadium-Substituted Phosphomolybdates and Phosphotungstates for Selective Aerobic Catalytic Oxidation of Benzyl Alcohol . Materials, 2022. 15(9): p. 3244. Yuan, W.-M., et al., A gas–liquid interface synthesis in polyoxometalate chemistry: potential bag filter for volatile organic amines . Journal of Chemical Sciences, 2018. 130(4): p. 47. El-Hakam, S.A., Thermal stability of vanadium substituted phosphomolybdic acid catalysts . Materials Letters, 2006. 60(28): p. 3338–3342. Additional Declarations No competing interests reported. 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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-8984427","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":605130180,"identity":"a3424e53-a7c1-4fdb-bf5d-4244976edad3","order_by":0,"name":"Shi Jinyi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvklEQVRIiWNgGAWjYDACCcYGgwQGBh5+ZuaDD0jTItnOlmxApBYobXCex0yAKB3ys5sbCh7uOCxjfJjBjIGhxiaaoBaDOwcbDBLPHOYxO8yQ9oDhWFpuA0EtEolALW1gLccNGBsOE9YiPwOqxbiZsU2CKC0MN6BaDJiZ2YjTYgDRks4jcZiN2SCBGL/Iz0h/Zvizzdqev//8xwcfamyIcBgDAxswBpshzAQilIMA8wMGhjoi1Y6CUTAKRsGIBAAKxz5LZn8IGQAAAABJRU5ErkJggg==","orcid":"","institution":"Jilin University of Chemical Technology","correspondingAuthor":true,"prefix":"","firstName":"Shi","middleName":"","lastName":"Jinyi","suffix":""},{"id":605130181,"identity":"3dda5523-3fe4-4d8b-be1d-774c14734ebf","order_by":1,"name":"Ding Yuansheng","email":"","orcid":"","institution":"Jilin University of Chemical Technology","correspondingAuthor":false,"prefix":"","firstName":"Ding","middleName":"","lastName":"Yuansheng","suffix":""}],"badges":[],"createdAt":"2026-02-27 06:54:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8984427/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8984427/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104563062,"identity":"22a89b7f-d6bf-47ff-b035-869c0f743de7","added_by":"auto","created_at":"2026-03-13 10:42:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":23877,"visible":true,"origin":"","legend":"\u003cp\u003eIR spectrum of charge transfer POMs [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8984427/v1/7565b9c48edac0c6cbda901d.png"},{"id":104563060,"identity":"5f7e58a5-7778-4eb6-aaf9-57047efb509c","added_by":"auto","created_at":"2026-03-13 10:42:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":23849,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray powder diffraction patterns of charge transfer POMs [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8984427/v1/a9afed395a272657c53574ae.png"},{"id":104563047,"identity":"7720196b-f52f-4410-ac4a-870b763fa44f","added_by":"auto","created_at":"2026-03-13 10:42:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":18576,"visible":true,"origin":"","legend":"\u003cp\u003eTG curve of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8984427/v1/52ae51a83bc6535a9ca8e2aa.png"},{"id":104563054,"identity":"1be30a98-0b1e-4fd7-8081-a718af1bf365","added_by":"auto","created_at":"2026-03-13 10:42:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":155780,"visible":true,"origin":"","legend":"\u003cp\u003e3D schematic diagram of the crystal structure of[(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8984427/v1/e50472b39cd53ae9c550d056.png"},{"id":104563061,"identity":"fb35a895-ce3a-4c5a-bc78-aaa4b5ac2d14","added_by":"auto","created_at":"2026-03-13 10:42:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":37871,"visible":true,"origin":"","legend":"\u003cp\u003eCatalytic activity experiments. (a) Effect of reaction time on yield, (b) Effect of catalyst dosage on yield, (c) Effect of hydrogen peroxide concentration on yield, (d) Effect of reaction temperature on yield.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8984427/v1/3c059e8421b5f7e5f7364e4e.png"},{"id":104782247,"identity":"ae1eb8cb-6438-49bb-b16b-f7a4593d9cbf","added_by":"auto","created_at":"2026-03-17 07:57:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1030823,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8984427/v1/b80b9062-3362-412d-911e-7752c853d48a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eSynthesis and Catalytic Oxidation Studies of a Novel Keggin-Type Complex Catalyst [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eheteropolyacids and their salts constitute a class of polyoxygen cluster metal complexes featuring spatial arrangements where the central atom (e.g. P, Si) and the coordinating atoms (polyatomic, e.g. Mo, W) are bridged by oxygen atoms[1]. They exhibit well-defined dimensions, shapes, and structures resembling discrete fragments of metal oxides. They play an increasingly vital role in fields such as catalysis[2, 3], photochemistry[4], medicine[5, 6], materials science[7, 8], and magnetism[9], attracting significant attention. As catalysts, heteropolyacids and their salts offer environmental friendliness, high catalytic activity, excellent selectivity, rapid reaction rates, mild reaction conditions, oxidative activity, optical and magnetic properties, along with superior stability and minimal equipment corrosion[2, 7, 8, 10]. They can function in both homogeneous and heterogeneous reactions, even as phase-transfer catalysts. As dual-functional green catalysts combining acidic and redox properties, they hold significant application potential. Conducting innovative research with substantial application potential in the field of green chemistry, particularly investigating the use of polyoxometalates as green catalysts in organic synthesis (such as alkylation and dealkylation of aromatics, esterification, dehydration/condensation, redox reactions, ring-opening, condensation, addition, and etherification reactions), holds immense significance. Therefore, synthesizing novel, highly efficient multimetallic oxoacid catalysts has become a hot topic.\u003c/p\u003e\n\u003cp\u003eThis study reports the first synthesis of a Keggin-type complex [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e as a polymetallic oxo-acid catalyst. The synthesized catalyst was characterized, and a systematic investigation of various factors influencing its catalytic performance in the oxidation of benzaldehyde to benzoic acid yielded promising results.\u003c/p\u003e"},{"header":"1 Experimental","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Main Reagents and Instruments\u003c/h2\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e, hexahydropyridine, and benzaldehyde (analytical grade, Shanghai Reagent Factory); H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2(\u003c/sub\u003e30%), NaH\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (analytical grade, Beijing Chemical Plant); Magna560 Fourier Transform Infrared Spectrometer (KBr pressing pellets, recording range 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; Nicolet Instruments, USA); Dmax 2200PC X-ray Powder Diffractometer (Rigaku Corporation, Japan); X-4 Digital Display Micro-Melting Point Apparatus (Beijing Tek Co., Ltd, China).; CT6-015 Thermal Analyzer (PerkinElmer, USA).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.2 Synthesis of the Parent Acid H\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u0026middot;nH₂O\u003c/h2\u003e \u003cp\u003eWeigh 8.13g of NaVO\u003csub\u003e3\u003c/sub\u003e, and dissolve in 37 mL of hot distilled water. Dissolve 2.36 g of NaH\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e in 20 mL of hot distilled water. Combine both solutions and reflux under stirring at 90\u0026deg;C for 90 min, then cool to room temperature. Slowly add approximately 2 ml concentrated sulfuric acid, controlling pH\u0026thinsp;\u0026asymp;\u0026thinsp;2. The solution changes from clear and transparent to dark red. Dissolve 40.3g Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e in 67 mL distilled water and add to the above solution. React for 30 min. Slowly add 28 ml concentrated sulfuric acid while stirring vigorously. After complete addition, react for 2 hours. During this process, the solution color gradually lightens, eventually becoming bright red. Add 100 ml of diethyl ether, shake vigorously, and allow to stand until layers separate. Collect the middle ether layer. Evaporate and concentrate in a fume hood over a 60\u0026deg;C water bath until a crystalline film forms on the liquid surface. Cool and allow the ether to evaporate completely to obtain bright red, transparent H\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e crystals. Recrystallize the crystals from the crude product using a mass ratio of approximately 1:1.2 (crystal: water).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e1.3 Preparation and Crystal Growth of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eDissolve a certain amount of H\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e\u0026middot;nH₂O in water to form a red transparent solution. Take a specific molar amount of hexahydropyridine and slowly add it to the red transparent solution under stirring. React at 70\u0026deg;C for 2 hours to produce a yellow-green precipitate. Filter the mixture. Wash the filter cake alternately with ethanol, diethyl ether, and water. After thorough washing, dissolve the cake in a proportionate mixture of acetonitrile and water. Filter again using quantitative filter paper to obtain a yellow-green transparent solution. Transfer the solution to a beaker, seal it with plastic wrap, and pierce the wrap with a needle to create uniform small holes. Allow the solution to slowly evaporate at room temperature in a well-ventilated, cool location. After approximately one week, yellow-green transparent crystals precipitated at the bottom of the beaker, identified as [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e crystals.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e1.4 Catalytic Activity Experiment\u003c/h2\u003e \u003cp\u003eWeigh equal masses of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e catalyst and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e(30%) were added to a 100 mL round-bottom flask. Under magnetic stirring, a certain amount of benzaldehyde was added dropwise, the temperature was raised to 75\u0026deg;C, and the reaction was carried out for 2.5 hours. The product was refrigerated for 24 hours. Filter and wash with saturated benzoic acid solution (to minimize loss), yielding white benzoic acid crystals. Dry the crystals, weigh them, and calculate the yield (mass fraction). Determine the melting point of the obtained product using a digital melting point apparatus.\u003c/p\u003e \u003c/div\u003e"},{"header":"2 Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Structural Characterization of the Catalyst\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.1.1 IR Spectroscopy Analysis of the Catalyst\u003c/h2\u003e \u003cp\u003eThe IR results indicate that the polyoxometalate charge-transfer complex [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e exhibits four characteristic absorption peaks corresponding to the parent heteropolyacid anion [PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e]\u003csup\u003e5\u0026minus;\u003c/sup\u003e. The P-Oa, Mo-Od, Mo-Ob-Mo, and Mo-Oc-Mo bond vibration peaks are at 1060.9, 962.1, 864.5, and 775.2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e relative to the parent acid[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In the newly synthesized polyoxometalate piperidine charge-transfer complex, these four characteristic absorption peaks are 1060.2, 957.5, 864.7, and 790.8 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The region between 700 and 1100 cm⁻\u0026sup1; represents the fingerprint absorption zone for polyanionic species. Comparison reveals that the newly synthesized charge-transfer complexes retain the Keggin structure of the polyanionic species, but the Mo-Ob-Mo and Mo-Oc-Mo absorption peaks exhibit a certain degree of blue shift, while the P-Oa and Mo-Od absorption peaks show a slight red shift. This occurs because in the newly synthesized polyoxometalate piperidine charge-transfer complexes, the charge from the protonated hexahydro-pyridine transfers to the polyoxometalate anion, exerting differential effects on various chemical bonds. This alters bond strengths, leading to red or blue shifts in absorption peaks. The absorption peaks of the polyoxometalate piperidine charge-transfer complexes in the wavenumber range of 1100\u0026ndash;1500 cm⁻\u0026sup1; correspond to the skeletal vibrations of the hexahydropyridine ring. Absorption vibrations above 3000 cm⁻\u0026sup1; originate from the stretching vibrations of C-H and N-H bonds in the hexahydropyridine structure. The presence of these absorption peaks indicates the existence of the hexahydropyridine moiety. These results suggest a strong charge transfer interaction between the polyanion and the counterion, leading to the formation of the polyoxometalate piperidine charge transfer complex.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.1.2 XRD Analysis of the Catalyst\u003c/h2\u003e \u003cp\u003eThe XRD results show that the synthesized [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e has four strong diffraction peaks at 2θvalues of 10.32\u0026deg;, 22.58\u0026deg;, 24.98\u0026deg;, and 30.92\u0026deg;. The positions and relative intensity of these peaks are very similar to the standard patterns of the Keggin-type heteropoly acid (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003ePMo\u003csub\u003e12\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e found in the library[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Also, comparing it with the cif file data for H\u003csub\u003e5\u003c/sub\u003e(PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e)\u0026middot;36H\u003csub\u003e2\u003c/sub\u003eO shows that both crystals display the typical diffraction patterns of Keggin-type salts in the 5\u0026deg;\u0026ndash;40\u0026deg; (2θ) range[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Specifically, the strongest peak below 10\u0026deg; belongs to the (110) plane, which is a clear sign that the Keggin anions are stacked along the \u003cem\u003ec\u003c/em\u003e-axis. In addition, there are groups of medium-intensity peaks in the 15\u0026deg;\u0026ndash;25\u0026deg; and 28\u0026deg;\u0026ndash;35\u0026deg; ranges. These peaks come from the complex atomic structure inside the [PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e]\u003csup\u003e5-\u003c/sup\u003e anion. However, there is a clear difference: all main peaks of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e are shifted to lower angles compared to H\u003csub\u003e5\u003c/sub\u003e(PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e)\u0026middot;36H\u003csub\u003e2\u003c/sub\u003eO. For example, the (110) peak moves from 9.7\u0026deg; to about 7.9\u0026deg;. According to Bragg\u0026rsquo;s Law, this shift means the interplanar spacing increases from 9.1 \u0026Aring; to 11.2 \u0026Aring;. This suggests that the large [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e cations (about 6\u0026ndash;7 \u0026Aring; in diameter) have filled the gaps between the Keggin anions, causing the crystal unit cell to expand slightly. This expansion is direct evidence from XRD that the organic molecules have successfully entered the inorganic structure.\u003c/p\u003e \u003cp\u003eIn addition, the peak intensities changed significantly. The peak near 22.0\u0026deg;, which belongs to planes like (222), is much stronger in the hybrid crystal. Since peak intensity depends on the type and position of atoms in the cell, this change reflects a difference in electron density. The organic cations have carbon and nitrogen atoms that are rich in electrons, replacing the water/protons (which have light atoms like H and O). This introduces new strong scattering centers, changing the overall electron density of the crystal.\u003c/p\u003e \u003cp\u003eFinally, adding the large and oriented organic amine cations significantly reduces the crystal symmetry. The crystal structure changes from the high-symmetry tetragonal system (P4/mnc) of H\u003csub\u003e5\u003c/sub\u003e(PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e)\u0026middot;36H\u003csub\u003e2\u003c/sub\u003eO to the monoclinic system (P2\u003csub\u003e1\u003c/sub\u003e/c) of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e. Due to the size and directional hydrogen bonds of the organic cations, the unit cell becomes distorted, so the axis lengths are no longer equal and the β angle is not 90\u0026deg;. This structural change is seen in the XRD results as a clear increase in the number of peaks and peak splitting, especially at low angles. As the symmetry becomes lower, the Mo/V atoms are more likely to be distributed in different positions, increasing the local structural differences[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.1.3 TG Analysis of Catalysts\u003c/h2\u003e \u003cp\u003eAnalysis of the thermogravimetric (TG) curve reveals that the weight loss of the polyoxometalate piperidine charge-transfer complex [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e occurs in three distinct stages. The first stage, spanning 199.04\u0026deg;C to 257.68\u0026deg;C, involves the loss of bound water molecules hydrogen-bonded to acidic protons, accounting for 1.215% of the total weight loss. The second stage, from 264.60\u0026deg;C to 433.36\u0026deg;C, involves weight loss from the cation of the polyoxometalate piperidine charge-transfer complex, accounting for 16.363% of the total weight loss; The third stage occurs from 693.20\u0026deg;C to 800\u0026deg;C, during which the anion undergoes complete decomposition with a weight loss of 27.603%. At this point, the polyoxometalate piperidine charge-transfer complex transforms into Mo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. The curve indicates that the decomposition temperature of this polyoxometalate piperidine charge-transfer complex is 433\u0026deg;C, whereas the theoretical decomposition temperature of its parent acid H\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e is 375\u0026deg;C[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The enhanced thermal stability of this crystal structure primarily stems from the hybridization of organic molecules with the parent acid. Here, the piperidine cation acts as a \u0026ldquo;molecular pillar,\u0026rdquo; filling the interstitial spaces of the Keggin anion. This not only prevents the framework from collapsing under reaction conditions but also inhibits the leaching and loss of active components through steric hindrance effects. This structure not only elevates the catalyst's thermal stability by approximately 60\u0026deg;C but also significantly enhances its tolerance to high concentrations of hydrogen peroxide (30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e).\u003c/p\u003e \u003cp\u003eBased on the above data, the molecular structure of the new compound can be established as [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e. Therefore, we employed MS software modeling to obtain the schematic 3D crystal structure of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The crystal structure of [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e exhibits the characteristic hybridization of an \u0026ldquo;inorganic framework-organic cation\u0026rdquo; assembly. The overall unit cell belongs to the monoclinic system with space group \u003cem\u003eP\u003c/em\u003e2\u003csub\u003e1\u003c/sub\u003e/\u003cem\u003ec\u003c/em\u003e. The inorganic framework core consists of a classic Keggin-type heteroanion [PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e]\u003csup\u003e5\u0026minus;\u003c/sup\u003e, which possesses a symmetrical cage structure. A phosphorus-oxygen tetrahedron (PO\u003csub\u003e4\u003c/sub\u003e) occupies the central position, tightly enclosed by ten molybdenum-oxygen octahedra (MoO\u003csub\u003e6\u003c/sub\u003e) and two vanadium-oxygen octahedra (VO\u003csub\u003e6\u003c/sub\u003e). These octahedra connect via shared oxygen vertices, forming a nearly spherical, rigid nanocluster. Two vanadium atoms (V\u003csup\u003e5+\u003c/sup\u003e) occupy positions originally intended for molybdenum in a disordered manner, preferring symmetry-related coordination sites. This coexistence of V and Mo generates V-O-Mo heterometallic bridges within the anion framework, introducing localized electron asymmetry and abundant redox active sites. Five positively charged piperidine cations[(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e cations with the negatively charged inorganic anionic framework through strong electrostatic interactions. Each pyridine ring (a five-membered saturated nitrogen-containing heterocycle) adopts a lower-energy chair conformation, with its -NH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e end interacting via hydrogen bonds and ionic bonds with oxygen atoms on the anion surface. This forms a spatial crystal structure characterized by a rigid anionic framework and flexible cationic fillers.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe use of heteropolyacids as catalysts has long been one of their most significant applications. The crystal phase [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e exhibits structural differences compared to traditional Keggin-type heteropolyacids, and these differences inevitably influence its catalytic performance. At the electronic structure level, the partial substitution of Mo by V generates heterometallic synergy effects. In the conventional PMo\u003csub\u003e12\u003c/sub\u003e structure, redox processes primarily rely on the Mo\u003csup\u003e6+\u003c/sup\u003e/Mo\u003csup\u003e5+\u003c/sup\u003e electron pair, which possesses relatively limited reduction potential. In contrast, the PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003e structure creates an electron-asymmetric environment where V\u003csup\u003e5+\u003c/sup\u003e interacts with Mo\u003csup\u003e6+\u003c/sup\u003e. The V\u0026thinsp;=\u0026thinsp;O bond is shorter and stronger than the Mo\u0026thinsp;=\u0026thinsp;O bond, endowing the V\u003csup\u003e5+\u003c/sup\u003e/V\u003csup\u003e4+\u003c/sup\u003e redox pair with a higher reduction potential. This modification lowers the activation energy barrier for hydrogen peroxide activation while providing more flexible electron transfer pathways, significantly enhancing the catalyst's oxidation capacity. More importantly, the introduction of piperidine cations enables precise regulation of the catalytic microenvironment. Traditional H-type Keggin acids, while highly acidic, often exhibit strong Br\u0026oslash;nsted acidity that promotes side reactions and are prone to dissolution and loss in aqueous solutions. In this catalyst, five [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e cations form hydrophobic channels of specific dimensions within the crystal lattice. This microenvironment exhibits preferential adsorption for certain organic molecules (e.g., benzaldehyde) while repelling the more hydrophilic hydrogen peroxide. This microenvironment preferentially adsorbs certain organic molecules (e.g., benzaldehyde) while moderately repelling more hydrophilic hydrogen peroxide and reaction intermediates. This facilitates in situ enrichment of substrates and timely desorption of products, effectively preventing the overoxidation of benzoic acid. Simultaneously, the piperidine cation weakens the catalyst's strong protonic acidity while enhancing its Lewis acidity characteristics. This allows the V\u003csup\u003e5+\u003c/sup\u003e sites to coordinate more selectively with specific functional groups (e.g., carbonyl oxygen), thereby improving the catalyst's selectivity. To evaluate the catalytic performance of the crystalline [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e, a classic chemical reaction was employed;the oxidation of benzaldehyde to benzoic acid catalyzed by polyoxometalates using H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. The experimental results are as follows.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Catalytic Activity Experiments\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Effect of Reaction Time on Yield\u003c/h2\u003e \u003cp\u003eUsing [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e as the catalyst, the effect of reaction time on catalytic activity was investigated under constant conditions, with results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) indicates that the yield gradually increases as the reaction time extends from 1.5 h to 2.5 h. Beyond this point, further increases in reaction time yield no change in the reaction yield, which remains essentially constant by 3.5 h. Therefore, the optimal reaction time is determined to be 2.5 hours.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Effect of Catalyst Dosage on Yield\u003c/h2\u003e \u003cp\u003eUsing [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e as the catalyst, the effect of catalyst dosage on catalytic activity was investigated under constant conditions, with results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b) indicates that when the molar ratio of catalyst to benzaldehyde exceeds 1.89\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e, the yield increases with rising molar ratio. between 1.89\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e and 2.84\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e, the increase exhibits linear growth with the most significant and pronounced magnitude. At this point, the effective utilization rate of hydrogen peroxide is significantly influenced by the catalyst dosage. When the molar ratio exceeds2.84\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e, the benzoic acid yield essentially remains constant. Therefore, the optimal molar ratio of the catalyst [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e to benzaldehyde is 2.84\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Effect of Hydrogen Peroxide on Yield\u003c/h2\u003e \u003cp\u003eUsing [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e as the catalyst, the effect of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e dosage on catalytic activity was investigated under constant conditions, with results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c) indicates that upon addition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the benzoic acid yield increases with rising H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e dosage, reaching a maximum at a molar ratio of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to benzaldehyde of 3.53:1. However, as the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e amount further increased, the benzoic acid yield slightly decreased. This indicates that excessive H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is detrimental to this oxidation reaction. This may occur because, at the reaction temperature, an excess of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e can cause a small portion of the benzoic acid to form its peroxide. Therefore, the optimal molar ratio of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e to benzaldehyde is 3.53:1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4 Effect of Temperature on Yield\u003c/h2\u003e \u003cp\u003eUsing [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e as the catalyst, the effect of reaction temperature on catalytic activity was investigated while other conditions remained constant. The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d) indicates that when the temperature exceeds 65\u0026deg;C, the reaction becomes significantly affected by temperature. The highest yield was achieved at 75\u0026deg;C. Further increasing the temperature beyond 75\u0026deg;C did not alter the reaction yield. Therefore, the optimal reaction temperature is determined to be 75\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e2.2.5 Blank Experiment\u003c/h2\u003e \u003cp\u003eIn this oxidation reaction, without adding a catalyst and keeping other conditions unchanged, the yield of benzoic acid is only about 27.5% when the optimal amount of 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is added. Moreover, the product exhibits a pale yellow color and a melting point ranging from 115.1\u0026deg;C to 119.1\u0026deg;C, with a significantly lower yield compared to the reaction without a catalyst. This demonstrates that the catalyst accelerates the oxidation reaction process, leading to a substantial increase in benzoic acid yield. If 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is omitted and the optimal amount of catalyst is added while maintaining other conditions constant, no benzoic acid is formed. This indicates that the catalyst does not possess oxidative functionality but instead catalyzes the oxidation reaction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e2.2.6 Verification Experiment\u003c/h2\u003e \u003cp\u003eTo verify the reliability of the optimal conditions determined in the experiments, three parallel experiments were conducted. The results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental Reaction Conditions (Verification Experiments)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003csub\u003ebenzaldehyde\u003c/sub\u003e:nH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReaction Temperature/\u0026deg;C\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003en\u003csub\u003eCatalyst\u003c/sub\u003e: n\u003csub\u003eBenzaldehyde\u003c/sub\u003e/\u0026times;10⁻⁴\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReaction Time/h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eYield/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1:3.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e87.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1:3.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e87.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1:3.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e86.87\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe experimental data in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e indicate that the optimal reaction conditions are: reaction temperature of 75\u0026deg;C; molar ratio of hydrogen peroxide to benzaldehyde of 3.53:1; molar ratio of catalyst to benzaldehyde of 2.84\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e:1; reaction time of 2.5 hours; and yield exceeding 85%.\u003c/p\u003e \u003cp\u003eThe results above demonstrate that [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e significantly enhances the catalytic efficiency of traditional Keggin catalysts through a dual strategy of V/Mo heterometallic synergy and organic cation microenvironment regulation. This organic-inorganic catalyst design concept offers a novel approach for developing highly efficient, stable, and selective polyacid-based oxidation catalysts, presenting broad application prospects.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3 Conclusions","content":"\u003cp\u003eThis study successfully designed and synthesized a novel organic-inorganic hybrid material [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e. IR and XRD structural analyses confirm that this material fully inherits the framework structure of the Keggin-type [PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e]\u003csup\u003e5\u0026minus;\u003c/sup\u003e anion. Simultaneously, the ordered incorporation of the [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e cation induces lattice expansion, redistribution of electron density, and enhanced long-range order, forming a unique supramolecular assembly.\u003c/p\u003e \u003cp\u003eIn the selective oxidation of benzaldehyde to benzoic acid, this catalyst demonstrates outstanding comprehensive performance; achieving 86% conversion and 100% selectivity under mild conditions, significantly outperforming conventional Keggin catalysts. Its outstanding performance stems from the ingenious combination of V/Mo heterometallic synergistic enhancement of redox capabilities and the hydrophobic microenvironment constructed by the piperidine cation; the former lowers the reaction energy barrier and accelerates H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation; the latter enriches organic substrates and promotes product desorption, thereby simultaneously enhancing catalytic activity, selectivity, and stability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by S. J. and D. Y.. The first draft of the manuscript was written by S. J., and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed during this study are included in this published article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable. This study does not involve human participants or animals.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHill, C.L., \u003cem\u003eIntroduction: Polyoxometalates\u003c/em\u003e. Chemical Reviews, 1998. 98(1): p. 1\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHill, C.L., \u003cem\u003ePreface: Polyoxometalates in catalysis\u003c/em\u003e. Journal of Molecular Catalysis A: Chemical, 2007. 262(1\u0026ndash;2): p. 1\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePaul, S., H. Hu, and M. Abon, \u003cem\u003eStructural Evolution under Reaction Conditions of Supported (NH4)3HPMo11VO40 Catalysts for the Selective Oxidation of Isobutane\u003c/em\u003e. Catalysts, 2015. 5(1): p. 461\u0026ndash;479.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, L., et al., \u003cem\u003eA new heterogeneous photocatalyst based on Wells\u0026ndash;Dawson polyoxometalate and nickel coordination compounds: synthesis, structure and property\u003c/em\u003e. Research on Chemical Intermediates, 2015. 41(3): p. 1691\u0026ndash;1702.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRhule, J.T., et al., \u003cem\u003ePolyoxometalates in Medicine\u003c/em\u003e. Chemical Reviews, 1998. 98(1): p. 327\u0026ndash;358.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhosh, S.K., R. Saha, and B. Saha, \u003cem\u003eToxicity of inorganic vanadium compounds\u003c/em\u003e. Research on Chemical Intermediates, 2015. 41(7): p. 4873\u0026ndash;4897.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRao, A.S., et al., \u003cem\u003ePolyoxometalates: Toward new materials\u003c/em\u003e. Journal of Chemical Sciences, 2011. 123(2): p. 229\u0026ndash;239.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, Y., et al., \u003cem\u003eRecent advances in polyoxometalate-based materials and their derivatives for electrocatalysis and energy storage\u003c/em\u003e. Materials Chemistry Frontiers, 2024. 8(3): p. 732\u0026ndash;768.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSahu, P.K., S. Kapurwan, and S. Konar, \u003cem\u003eEpitome of polyoxotungstate-coordinated lanthanide-based single-molecule magnets.\u003c/em\u003e Chemical Communications, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, H., et al., \u003cem\u003eDeep Oxidative Desulfurization of Fuels Catalyzed by Ionic Liquid-Type Phosphomolybdates\u003c/em\u003e. Energy \u0026amp; Fuels, 2009. 23(3): p. 1354\u0026ndash;1359.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, Y., S. Li, and Y. Kong, \u003cem\u003eHydroxylation of benzene to phenol over heteropoly acid H5PMo10V2O40 supported on amine-functionalized MCM-41\u003c/em\u003e. RSC Advances, 2021. 11(43): p. 26571\u0026ndash;26580.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFournier, M., et al., \u003cem\u003eVanadium-substituted 12-molybdophosphoric acids: Syntheses, stability and characterization of the pure 1, 2 and 3 vanadium species\u003c/em\u003e. Journal of Materials Chemistry, 1992. 2(9): p. 971\u0026ndash;978.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eScalerandi, G.S., F.E. Tuler, and L.R. Pizzio, \u003cem\u003eTetrabutyl Ammonium Salts of Keggin-Type Vanadium-Substituted Phosphomolybdates and Phosphotungstates for Selective Aerobic Catalytic Oxidation of Benzyl Alcohol\u003c/em\u003e. Materials, 2022. 15(9): p. 3244.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan, W.-M., et al., \u003cem\u003eA gas\u0026ndash;liquid interface synthesis in polyoxometalate chemistry: potential bag filter for volatile organic amines\u003c/em\u003e. Journal of Chemical Sciences, 2018. 130(4): p. 47.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Hakam, S.A., \u003cem\u003eThermal stability of vanadium substituted phosphomolybdic acid catalysts\u003c/em\u003e. Materials Letters, 2006. 60(28): p. 3338\u0026ndash;3342.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"piperidinium phosphomolybdovanadate, Keggin polyoxometalate, Catalysis, Benzoic acid","lastPublishedDoi":"10.21203/rs.3.rs-8984427/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8984427/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDeveloping efficient and robust polyoxometalate catalysts is highly desirable for green organic oxidation. In this work, we synthesized a novel organic-inorganic hybrid Keggin-type complex, [(CH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e5\u003c/sub\u003eNH\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e5\u003c/sub\u003ePMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e, via the assembly of phosphomolybdovanadic acid and piperidine. Structural analyses using FT-IR and XRD confirmed that the parent [PMo\u003csub\u003e10\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e40\u003c/sub\u003e]\u003csup\u003e5\u0026minus;\u003c/sup\u003e framework remains fully intact. Meanwhile, the intercalation of piperidinium cations expands the crystal lattice and induces a unique monoclinic supramolecular architecture. Thermogravimetric analysis revealed a significant enhancement in thermal stability, with the material resisting decomposition up to 433\u0026deg;C. We evaluated the practical utility of this complex in the selective oxidation of benzaldehyde to benzoic acid using aqueous H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Under mild optimized conditions (75\u0026deg;C, 2.5 h), the catalyst achieved an 87% yield with absolute selectivity. This exceptional performance originates from two distinct structural advantages. The V/Mo heterometallic interaction inherently boosts the overall redox capacity, facilitating rapid oxidant activation. Concurrently, the organic cations construct a localized hydrophobic microenvironment within the lattice. This specific pocket selectively adsorbs the organic substrate and repels excess hydrophilic oxidants, thereby accelerating the reaction while effectively suppressing overoxidation.\u003c/p\u003e","manuscriptTitle":"Synthesis and Catalytic Oxidation Studies of a Novel Keggin-Type Complex Catalyst [(CH2)5NH2]5PMo10V2O40","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-13 10:41:45","doi":"10.21203/rs.3.rs-8984427/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-30T01:26:40+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-27T12:49:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"132523928616357538228485518442786743788","date":"2026-04-14T05:13:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"233519656288713633748874305663741735517","date":"2026-04-13T06:14:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-26T05:36:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"3362404896894165948702388723370736297","date":"2026-03-16T09:36:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"87051787428989653605550602250964305131","date":"2026-03-12T13:57:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"259632406364414950978854621085267248349","date":"2026-03-11T08:58:31+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-10T13:42:03+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-04T02:51:03+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-04T02:49:54+00:00","index":"","fulltext":""},{"type":"submitted","content":"Research on Chemical Intermediates","date":"2026-02-27T06:37:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"research-on-chemical-intermediates","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rint","sideBox":"Learn more about [Research on Chemical Intermediates](http://link.springer.com/journal/11164)","snPcode":"11164","submissionUrl":"https://submission.nature.com/new-submission/11164/3","title":"Research on Chemical Intermediates","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3c55b2c9-f646-420d-b82f-ddbf12a3307f","owner":[],"postedDate":"March 13th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-04-30T01:26:40+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-12T08:42:19+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-13 10:41:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8984427","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8984427","identity":"rs-8984427","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}