Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single−atom Cu/O Lewis pair for acetylene hydrochlorination

Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single−atom Cu/O Lewis pair for acetylene hydrochlorination | 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 Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single−atom Cu/O Lewis pair for acetylene hydrochlorination Chaofeng Huang, Junchen Peng, Dandan Dong, Zongyuan Wang, Hong Yang, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2361952/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Simultaneously boosting acetylene hydrochlorination activity and avoiding formation of explosive copper acetylide over Cu-based catalyst, which represented a promising alternative to Hg-based and noble metal catalysts, remained challenging. Herein, we fabricated a frustrated single−atom Cu/O Lewis pair catalyst (Cu/O−FLP) by coupling epoxide group (C−O−C) with atom-dispersed Cu−cis−N2C2Cl center to address this challenge. The basic epoxy site modulated the electron-deficient state of Lewis-acidic Cu center and paired with the Cu−cis−N2C2Cl moiety to preferentially break HCl into different electronegative Cu−Clδ− and C−O−Hδ+ intermediates, which further induced both an extra localized electric field to polarize acetylene and a upshift of the d-band center of catalyst, thereby promoting adsorption and enrichment of acetylene by enhancing the dipolar interaction between acetylene and active intermediates. Moreover, the generated Cu−Clδ− and C−O−Hδ+ drastically reduced the energy barrier of rate-limiting step and made vinyl chloride easier to desorb from the Lewis-basic oxygen-atom site rather than traditional Lewis-acidic Cu center. These superiorities ensured a higher activity of Cu/O-FLP compared with its counterparts. Meanwhile, preferential dissociation of HCl endowed single-atom Cu with the coordination-saturated configuration, which impeded formation of explosive copper acetylide by avoiding the direct interaction between Cu and acetylene, ensuring the intrinsic safety during catalysis. Physical sciences/Energy science and technology Physical sciences/Materials science Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Acetylene hydrochlorination represented one of important industrial reactions for producing vinyl chloride monomer, which was widely used for polyvinylchloride (PVC). 1 To date, activated carbon supported mercuric chloride as a common acetylene hydrochlorination catalyst had triggered numerous environmental problems due to high toxicity and easy sublimation. Although various mercury-free catalysts such as noble-metal Au, 2 – 6 Pt, 7 Ru, 8 – 11 Pd, 12 , 13 noble metal alloy and metal-free doped carbon 14 – 16 had been extensively developed, many of these alternatives generally suffered from several limitations, including expensive price, carbon deposition, 17 cationic metal over-reduction 18 and/or leaching. 19 By contrast, the atom − dispersed Cu anchored on carbon matrix was recently concerned due to potential activity for acetylene hydrochlorination as well as the maximal atom utilization and high theoretically initial activity. 20 Moreover, the electronic configuration and coordination environment/number of carbon-supported single-atom Cu site were facile to be regulated by various doped heteroatoms, including N and P. 21 – 24 These single-atom Cu catalysts tended to catalyze acetylene hydrochlorination via a critical initial step that the active Cu sites were generally prone to pre-adsorb acetylene, which was followed by the H − Cl bond cleavage to form vinyl chloride. However, the high symmetry of acetylene molecule made the electron cloud of carbon-carbon triple bond (C ≡ C) difficult to be polarized, compared with the polar H − Cl bond. This probably affected the hydrochlorination performance of catalysts. In addition, for most single-atom Cu catalysts that used N or P doped carbon as supports, not all N/P heteroatoms were coordinated with Cu atoms. 22 , 23 Theoretically, these uncoordinated N/P heteroatoms in the doped carbon supports could be regarded as the solid base due to their electron-rich features. Thus, in the presence of these uncoordinated N or P basic dopants, preferential adsorption of acetylene over the single-atom Cu site immobilized on the N/P − doped carbon possibly resulted in a potential risk of forming copper acetylide, which belonged to hazardous explosive ( Scheme S1 ). Especially, when these single-atom Cu catalysts were applied for acetylene hydrochlorination on a large scale, the explosive risk originating from formation of copper acetylide at high temperature possibly rose. Thus, a reasonable consideration was whether HCl could be preferentially adsorbed, activated and broken into H δ+ and Cl δ– intermediates at active sites. If possible, this would avoid the risk of producing copper acetylide at Cu site by impeding the direct interaction between Cu and acetylene. Furthermore, owing to the different electronegativity, the formed H δ+ and Cl δ– were conducive to inducing an extra local electric field around active sites to enhance polarization of electron cloud of C ≡ C to promote subsequent acetylene hydrochlorination. The recently proposed frustrated Lewis acid − base pair (FLP) showed great potential in activating and cleaving chemical bonds of various gaseous molecules, including H 2, 25 N 2, 26 , 27 and CO 2 . 28 , 29 The heterolytic cleavage of H–Cl bond would produce H δ+ and Cl δ– species, which belong to Brønsted acid and Lewis base, respectively. In principle, dissociating the H–Cl bond was probably achieved by fabricating the single − atom Cu/O pair as FLP site. This would give rise to active Cu − Cl δ– and O − H δ+ species at this atom-dispersed Cu/O FLP site, which contributed to inducing a polarization filed because of the electronegativity difference between H δ+ and Cl δ– to promote subsequent acetylene hydrochlorination. However, preferential cleavage of H–Cl bond over the single − atom Cu/O FLP site to enhance acetylene hydrochlorination and avoid forming copper acetylide at Cu sites was seldom reported. Herein, we constructed a single − atom Cu/O − FLP catalyst consisting of the atom − dispersed Cu − cis − N 2 C 2 Cl center (i.e., Cu coordinated with two N and two C atoms in the cis − configuration and an axial Cl atom) and functional epoxide (C − O−C) group, which acted as FLP sites to activate and cleave H − Cl bond, giving rise to the Cu − Cl δ– and C − O−H δ+ species at catalytic sites during HCl pre − activation. This both upshifted the d-band center of catalyst toward Fermi level and induced an extra local electric field to polarize the electron cloud of acetylene, thereby promoting the enrichment and adsorption of acetylene. Meanwhile, preferential dissociation of HCl reduced the energy barrier of rate-limiting step and ensured the easier desorption of formed vinyl chloride over the Lewis-basic oxygen atom site, rather than Lewis-acidic Cu site. As a result, the HCl − activated Cu/O − FLP presented an enhanced catalytic activity for acetylene hydrochlorination. In addition, the newly formed Cu − Cl δ− could impeded the direct interaction between Cu and C 2 H 2 , improving the intrinsic safety by avoiding forming explosive copper acetylide. Results And Discussion To fabricate frustrated single−atom Cu/O Lewis pair site over doped carbon support, we chose imidazolium ionic liquid, CuCl 2 and glucose as precursors. After hydrothermal reaction, pyrolysis at 600 o C and nitric acid treatment, the catalyst with single−atom Cu/O Lewis pair site was obtained (See more synthesis details in Experimental Section of Supporting Information) and labelled as Cu/O−FLP. According to X−ray diffraction (XRD) analysis, no obvious Cu−related crystalline peaks was observed in Cu/O−FLP, except the graphitic carbon peaks ( Figure S1 ), indicating that Cu was dispersed in the atomic form or small nanoparticles/clusters. To further confirm the existing form of Cu, we used spherical aberration corrected high−angle annular dark-field scanning transmission electron microscope (HAADF−STEM) to observe the morphology of Cu/O−FLP. Figure 1a showed that numerous isolated Cu atoms were anchored in the doped carbon matrix, agreeing well with the XRD result. The energy-dispersive X−ray spectroscopy (EDS) mapping displayed that Cu/O−FLP contained C, N, O, Cl and Cu elements, which were uniformly distributed in sample ( Figure 1b ). The corresponding Cu content was determined to be 4.1wt.% according to inductively coupled plasma optical emission spectrometer (ICP−OES) measurement. Moreover, the surface area (631 m 2 /g) and micro-mesoporous structure (> 1 nm) were determined by Brunauer−Emmett−Teller (BET) measurements ( Table S1 and Figure S2 ), which was expected to promote the exposure of single−atom Cu/O FLP site and fast mass transfer of HCl and acetylene to catalytic sites for enhancing hydrochlorination activity of catalyst, respectively. The chemical state of Cu in Cu/O−FLP was investigated using X−ray photoelectron spectroscopy (XPS). The Cu 2p XPS spectrum ( Figure S3 ) discovered that the dominant oxidation state of Cu located in the region of +1 and +2, similar to many reported Cu single−atom carbonaceous materials. 30-33 According to N 1s XPS spectrum ( Figure 1c ), Cu-coordinated N (Cu−N x ) species was obviously observed in Cu/O−FLP, except the pyrrolic, pyridinic, graphitic and oxidative N. 34-36 In the O 1s XPS spectrum ( Figure 1d ), C−OH, C−O−C and C=O were presented in Cu/O−FLP, 37 which was also supported by Fourier transform infrared spectroscopy (FT−IR) ( Figure S4 ). Meanwhile, no Cu−O bond was found in O 1s XPS spectrum, 38 excluding the existence of Cu−O coordination bond. The Cl 2p XPS spectrum revealed that there existed Cu−Cl bond in Cu/O−FLP ( Figure 1e ). 39,40 These XPS results indicated that the first coordination shell of atom−dispersed Cu sites contained N and Cl atoms. To deeply disclose the local coordination environment of single-atom Cu in Cu/O−FLP, X−ray absorption near-edge structure (XANES) and extended X−ray absorption fine structure (EXAFS) spectroscopic measurements were conducted, and Cu foil, copper oxide (CuO), cuprous oxide (Cu 2 O), cupric chloride (CuCl 2 ) and copper phthalocyanine (CuPc) were used as reference. As depicted in Cu K−edge XANES spectrum ( Figure 2a ), the rising absorption edge of Cu/O−FLP was situated between those of Cu 2 O and CuO, indicating that the average valence state of single-atom Cu δ+ was 1 < δ < 2, in consistent well with the Cu 2p XPS result. Through k 3 −weighted Fourier−transform, the first coordination shell of atom−dispersed Cu in Cu/O−FLP appeared at 1.50 and 1.90 Å in the R space EXAFS spectra, which corresponded to the Cu−C/N/O and Cu−Cl bonds, respectively ( Figure 2b ). The Cu−O bond was excluded according to the O 1s XPS spectrum ( Figure 1d ). Nevertheless, it was still difficult to distinguish Cu−N and Cu−C bonds from the R space EXAFS spectrum, due to their similar bond lengths. In addition, compared with the standard Cu foil, no obvious Cu−Cu characteristic peaks was found in Cu/O−FLP ( Figure 2c ). In the wavelet transform (WT) contour plots, the maximum intensity of Cu/O−FLP located at 4.6 Å -1 obviously distinct from that of Cu foil, further confirming the atomic dispersion of Cu species in Cu/O−FLP ( Figure 2d ). The further fitting result disclosed that the coordination number of single−atom Cu approached five, which consisted of four N/C atoms and one Cl atom ( Table S2 ), indicating that the Cu atoms were mainly dispersed on the doped carbon matrix with the Cu−N x C 4-x Cl (1 ≤ X ≤ 4) moiety. To further determine the most probable local coordination configuration of Cu atom, we performed time−of−flight secondary ion mass spectrometry (TOF−SIMS) measurement. 41 As shown in Figure 2e , the negative fragment ion peaks in the mass region m/z = 114.5−117.5 could be obvious detected during Bi 3+ ions beam sputtering on Cu/O−FLP, which corresponded to the Cu and Cu isotope of CuC 2 N 2 – units. The TOF−SIMS negative ion imaging also directly observed the detected CuC 2 N 2 – fragments. Moreover, we found that the Cl negative ions presented an obvious enrichment in the position with abundant CuC 2 N 2 – fragments. Combining the TOF−SIMS, EXAFS and XPS results, it could be inferred that the Cu−N 2 C 2 Cl configuration probably existed in the matrix of Cu/O−FLP. Meanwhile, Figure 2a revealed that the intensity of the 1s→4p z transition peak (8985eV) 42,43 in the Cu K−edge XANES spectrum of Cu/O-FLP drastically decreased compared with that in CuPc ( Figure 2a ), indicating the low symmetry of Cu−N 2 C 2 Cl motif. This hinted the Cu atom in Cu−N 2 C 2 Cl moiety of Cu/O−FLP probably coordinated with two C and two N atoms in the cis−configuration, which would be discussed in the following part. Next, we evaluated the acetylene hydrochlorination performance of as−synthesized Cu/O−FLP. The control samples, including N−free active carbon−supported CuCl 2 (CuCl 2 /AC) and Cu−free N−doped carbon (N/C) were chosen as references (See Experimental Section in Supporting Information). Interestingly, it was found that HCl pre-activation could significantly boost the acetylene hydrochlorination performance of Cu/O−FLP compared with C 2 H 2 pre−activation and unactivated samples ( Figure 3a , HCl and C 2 H 2 −pretreated Cu/O−FLP were denoted as Cu/O−FLP−HCl and Cu/O−FLP−C 2 H 2 , respectively, see more details of pre−activation treatment in Supporting Information). The conversion efficiency of acetylene over Cu/O−FLP−HCl reached 59.4 % during 9 h operation ( Figure 3a ), which obviously exceeded those of Cu/O−FLP−C 2 H 2 (33.4%) and the untreated Cu/O−FLP (46.05%), implying that HCl pretreatment probably modulate the microstructure of active sites to alter the catalytic pathway. These catalysts showed ~100% selectivity for vinyl chloride under the same condition ( Figure S5 ), but the yield and turnover frequency of Cu/O−FLP−HCl were significantly superior to those of Cu/O−FLP−C 2 H 2 catalyst ( Figure 3b ). Furthermore, Cu/O−FLP−HCl also presented a higher acetylene conversion efficiency than CuCl 2 /AC (25.4 %) and N/C (1.76 %) ( Figure 3c ). Considering that CuCl 2 /AC and N/C did not contain N dopant and Cu atom, respectively, the above catalytic data directly demonstrated the crucial role of N−coordinated single−atom Cu center of Cu/O−FLP in efficiently catalyzing acetylene hydrochlorination to form vinyl chloride. To further confirm whether the Lewis-acidic Cu in local Cu−N 2 C 2 Cl configuration was the active site for acetylene hydrochlorination, we used ethylenediaminetetraacetic acid (EDTA) as chelating agent to remove Cu ions of Cu/O−FLP by stirring them in aqueous solution. After 24 h, the mixture was centrifugated. UV−Vis spectrum of the supernatant displayed an obvious adsorption at 271 nm ( Figure S6 ), which was assigned to EDTA−Cu complex, indicating successful removal of Cu ions. 44 The corresponding performance measurement showed that removal of Cu ions resulted in a 22.1 % decrement of the acetylene conversion efficiency after 9 h duration, suggesting the Lewis-acidic Cu in the localized Cu−N 2 C 2 Cl configuration was the active site of Cu/O−FLP for acetylene hydrochlorination ( Figure 3d ). To explore why HCl pre−activation enhanced the catalytic performance of Cu/O−FLP compared with C 2 H 2 pre-activation, temperature programmed desorption (TPD) experiments were employed to investigate the different absorption strength of Cu/O−FLP for HCl and C 2 H 2 . As shown in Figure S7 , the HCl desorption occurred at a higher temperature, compared with the C 2 H 2 desorption. This manifested the stronger bonding strength of Cu/O−FLP for HCl, signifying that the active site probably tended to preferentially adsorb and activate HCl during acetylene hydrochlorination. 45 To identify the crucial role of oxygen atom in doped carbon matrix during HCl pre-activation, the O 1s XPS spectra of Cu/O−FLP before and after HCl pre-treatment were collected. Figure 4a disclosed that after HCl pre−activation, the content of C−O−C obviously decreased, which was accompanied with the increment of C−OH content. This implied that the C−O−C was probably the epoxide group and the H−Cl bond could be ruptured by protonating and cleaving the epoxide group via a ring-opening reaction to form the C−OH bond. In this sense, the electron−rich oxygen atom in the epoxide group played the role of Lewis basic site during the H−Cl cleavage, which accepted the proton of HCl to produce C−O−H δ+ . On the other hand, the single−atom Cu was demonstrated to be the catalytic site according to the above EDTA−poisoning experiment ( Figure 3d ). In the Cu−N 2 C 2 Cl site of Cu/O−FLP, the single−atom Cu essentially belonged to Lewis acid due to its positive chemical valance. The Cl atom of HCl possessed more negative charge because of its stronger electronegativity. In this regard, the H δ+ and Cl δ– atoms in HCl could be seen as Brønsted acid and Lewis base, respectively. Given that the O atom (Lewis base) in the C−O−C group interacted with HCl and accepted its H δ+ atom (Brønsted acid), we thus considered that whether the Cu atom (Lewis acid) in the Cu−N 2 C 2 Cl site probably accepted the Cl δ– atom (Lewis base) of HCl to form the extra Cu−Cl δ– and promoted the scission of H−Cl bond by cooperating with the O atom (Lewis base) of the C−O−C group during HCl pre−activation. To evidence the formation of extra Cu−Cl δ– during HCl pre-activation, XANES and EXAFS spectroscopic measurements were conducted. According to the Cu K−edge XANES spectra ( Figure 4b ), the Cu/O−FLP−HCl showed an enhanced white line intensity, hinting that the Cu atom in Cu/O−FLP−HCl possessed a higher oxidation state compared with the pristine Cu/O−FLP in correspondence with the Cu 2p XPS result ( Figure S8 ). 46 This suggested the coordination environment of Lewis-acidic Cu site had been altered after HCl pre−activation, which was also supported by the corresponding R space EXAFS spectrum. As depicted in Figure 4c , the Cu in Cu/O−FLP−HCl still maintained the formation of atomic dispersion, and the main peak intensity of Cu/O−FLP−HCl was obviously higher than that of the pristine Cu/O−FLP, indicating that the coordination number of atom−dispersed Cu in Cu/O−FLP−HCl increased. 47 The fitting data further provided experimental proof, which displayed that the single−atom Cu in Cu/O−FLP−HCl was connected by six atoms, involving two N, two C and two Cl atoms ( Table S2 ). Compared with Cu/O−FLP, the extra increase of Cl atom at the first coordination shell of single-atom Cu in Cu/O−FLP-HCl strongly demonstrated the formation of extra Cu−Cl δ– during HCl pre−activation. In theory, introducing the extra Cu−Cl δ– bond into the original Cu−N 2 C 2 Cl site by cleaving H−Cl bond would lead to the saturated coordination configuration of single−atom Cu (i.e., Cu−N 2 C 2 Cl 2 ). We thus used NH 3 −TPD to further verify the formation of extra Cu−Cl bond in Cu/O−FLP−HCl. As shown in Figure 4d , the pristine Cu/O−FLP exhibited two typical desorption peaks at 112 o C and 294 o C before HCl pre−activation, corresponding to Brønsted acid site and Lewis acid site, respectively. Once pre−activated by HCl, the NH 3 desorption peak of the Lewis-acidic Cu site almost disappeared. This directly confirmed the formation of extra Cu−Cl bond again, which resulted in a saturated coordination configuration of single−atom Cu site, making NH 3 difficult to be adsorbed at Lewis-acidic Cu site. Such a result was also confirmed by the in−situ IR spectra of adsorbed pyridine detected at 350 o C ( Figure S9 ). It displayed that the pyridine adsorption peak of Lewis-acidic Cu site in the Cu/O−FLP−HCl drastically decreased compared with Cu/O−FLP, which resulted from the site−blocking effect of extra Cl atom at the atomic Cu center. Moreover, according to the NH 3 −TPD result, it can be found that the desorption peak intensity of Brønsted acid site (112 o C) obviously increased, manifesting the new generation of C−OH group with Brønsted acidity (O−H δ+ ) during HCl pre−activation, which was expected to facilitate the protonation step of C≡C bond of C 2 H 2 . On the basis of all the above data, it could be concluded that the oxygen atom of C−O−C group and single−atom Cu played the roles of frustrated Cu/O Lewis acid−base pair, which corporately participated in the HCl activation and broke H−Cl bond to form C−O−H δ+ and Cu−Cl δ– intermediates at Cu/O FLP active sites. More importantly, the H−Cl bond cleavage provided the extra Cl atom for Cu and endowed single−atom Cu with the saturated coordination configuration at its first coordination shell (i.e., Cu−N 2 C 2 Cl 2 ), which effectively impeded the direct interaction between Cu and C 2 H 2 , avoiding a potential risk of forming explosive copper acetylide. According to the above discussions, the atom−dispersed Cu center in Cu/O−FLP catalyst formed the stable six−coordination structure after dissociating HCl. That is, the Cu site coordinated with two C, two N and two Cl atoms. Theoretically, the single−atom Cu−N 2 C 2 Cl coordination center in the pristine Cu/O−FLP catalyst possessed two possible conformations, i.e., Cu coordinated with two N and two C atoms in the cis−configuration (Cu− cis −N 2 C 2 Cl) or Cu connected by two N and two C atoms in the trans−configuration (Cu− trans −N 2 C 2 Cl). In the two kinds of possible conformations, we herein considered four different structures (i.e., Cu− cis −N 2 C 2 Cl−O1, Cu− cis −N 2 C 2 Cl−O2, Cu− cis −N 2 C 2 Cl−O3 and Cu− trans −N 2 C 2 Cl−O4) according to the different location between the O atom of epoxide (C−O−C) group and the Cu−N (or Cu−C) bond ( Figure S10 ). To ascertain the optimum Cu/O FLP site structure that could stably dissociate the H−Cl bond, Bader charge analysis was performed to estimate the oxidation states of Cu in these four different structures. 48 Figure 4e showed that the calculated valence states of Cu in Cu− cis −N 2 C 2 Cl−O1 and Cu− trans −N 2 C 2 Cl−O4 configurations were obviously higher than those in Cu− cis −N 2 C 2 Cl−O2 and Cu− cis −N 2 C 2 Cl−O3 configurations. In theory, the higher valence state of single−atom Cu, which signified a more electron−deficient characteristic, would be beneficial to stabilizing the Cl δ– atom that originated from the HCl dissociation by enhancing the Cu−Cl δ– bond strength. In order to verify this, the structural stability analysis was further conducted according to theoretical DFT canulations. As displayed in Figure S10 , only Cu− cis −N 2 C 2 Cl−O1 was capable to cleave H−Cl bond to form the stable six−coordination configuration at its first coordination shell (i.e., Cu−N 2 C 2 Cl 2 ), matching well with the experimental result. In addition, the theoretical valance of Cu− cis −N 2 C 2 Cl−O1 obtained by Bader charge analysis approached the Cu 2p XPS calculated data ( Figure S8 ). However, another three single−atom Cu/O FLP configurations were well excluded, because they could not either exist stably or form the stable six−coordination configuration at Cu center after HCl pre-activation. To further confirm this optimum Cu− cis −N 2 C 2 Cl−O1 configuration, we performed XANES modeling based on Finite Difference Method Near Edge Structure (FDMNES) calculation, which was usually reported to identify the metal single−atom coordination structure of M−N−C. 49 Figure 4f showed that the experimental simulation spectra presented a relatively satisfactory agreement on the basis of the Cu− cis −N 2 C 2 Cl−O1 model. Moreover, the corresponding differential charge density analysis discovered that when the epoxide group existed in the vicinal location of Cu− cis −N 2 C 2 Cl center, the charge state of single−atom Cu became more positive due to the inductive effect of oxygen atom in functional epoxide group, in agreement with the previous report 37 ( Figure 4g and Figure 4h ). This also supported the experimental observation that the extra Cl δ– atom originating from the HCl dissociation could be stabilized by the more electron−deficient Cu via formation of the Cu−Cl δ– bond. Meanwhile, once the electron of single-atom Cu site flowed to the high-electronegative O atom of epoxide group, this would give rise to the more electron-rich environment around the O atom, which helped the epoxide group to accept the H δ+ atom of HCl via the ring-opening reaction. As a result, the electron-rich epoxide group cooperated with the more positive charged Cu atom to promote the key step of H−Cl adsorption and dissociation. All of these data indicated that the atom−dispersed Cu in Cu/O−FLP catalyst was probably incorporated in doped porous carbon matrix via a local configuration of Cu− cis −N 2 C 2 Cl, and the epoxide group was probably situated in the vicinal location of Cu− cis −N 2 C 2 Cl center. Moreover, such a vicinal oxygen atom in the epoxide group not only modulated the electron−deficient state of Cu center but also paired with atom−dispersed Cu to work as frustrated Cu/O Lewis acid−base pair, which activated HCl and broke H−Cl bond to form stable C−O−H δ+ and Cu−Cl δ– intermediates for acetylene hydrochlorination. The obvious electronegativity difference arising from the newly formed Cl δ– and H δ+ at the Cu/O FLP site tended to induce a local polarized electric field, which would contribute to enhancing the electron cloud polarization of C≡C in the highly symmetric acetylene molecule ( Figure 5a ). This probably promote the C 2 H 2 enrichment and adsorption by improving the dipolar interaction between C 2 H 2 and active Cu−Cl δ– /C−O−H δ+ species, thereby facilitating acetylene hydrochlorination. To experimentally verify this, we destructed Cu/O FLP site by choosing EDTA to remove Cu and obtained Cu/O−FLP(EDTA) catalyst, which was further pretreated by HCl to produce Cu/O−FLP(EDTA) −HCl. The subsequent TPD result revealed that the desorption amount of C 2 H 2 over Cu/O−FLP(EDTA) −HCl significantly decreased compared with that over Cu/O−FLP−HCl ( Figure S11 ), which was attributed to the difficult cleavage of the H−Cl bond because of destruction of FLP site, making the extra local electric field unformed. As a result, C 2 H 2 was difficult to be polarized, thereby causing a poor C 2 H 2 adsorption. This further supported that dissociation of HCl over Cu/O FLP site could induced a local polarized electric field to promote C 2 H 2 adsorption and enrichment. Ultraviolet photo−electron spectroscopy (UPS) was also employed to investigate the d-band center of catalyst, 50,51 which could act as an indicator to indicate the interaction strength between catalyst and adsorbate. Figure 5b illustrated that the d−band center of Cu/O−FLP−HCl obviously upshifted toward Fermi level compared with Cu/O−FLP, leading to a higher desorption peak intensity of C 2 H 2 over Cu/O−FLP-HCl ( Figure 5c ), which supported the above result. In addition, the desorption energy of formed vinyl chloride over Cu/O−FLP−HCl was obviously lower than that over Cu/O−FLP−C 2 H 2 ( Figure 5c ). These implied that preferential cleavage of HCl into active Cu−Cl δ– /C−O−H δ+ species promoted the adsorption and enrichment of C 2 H 2 by the electric-field-induced dipolar interaction and upshifting the d-band center of catalyst and the desorption of vinyl chloride. Moreover, once vinyl chloride was formed, the local polarized electric field would sharply decrease ( Figure 5a ), due to the disappearance of active Cl δ– and H δ+ species at Cu/O FLP site. As a result, the vinyl chloride product rapidly desorbed from the catalytic site, thereby regenerating the Cu/O Lewis pair center. Similar to Cu/O−FLP−HCl, the R space EXAFS spectrum of Cu/O−FLP−C 2 H 2 also exhibited an obvious enhanced main peak intensity compared with that of the original Cu/O−FLP ( Figure S12 ), which was attributed to the adsorption of C 2 H 2 , thereby increasing the coordination number of single−atom Cu site. However, the Cu K−edge XANES and Cu 2p XPS spectra showed that the valance of Cu/O−FLP−C 2 H 2 was significantly lower than that of Cu/O−FLP−HCl, but higher than that in the pristine Cu/O−FLP ( Figure S8 ). Such a result indicated that the interaction between C 2 H 2 and Cu was poorer than that between HCl and Cu, coinciding with the TPD data ( Figure S7 ). This promoted HCl to better compete with C 2 H 2 for the catalytic site of Cu/O−FLP, which could explain why the pristine Cu/O−FLP presented an increased activity compared with Cu/O−FLP−C 2 H 2 during acetylene hydrochlorination ( Figure 3a ). Based on R space EXAFS spectrum, the catalytic Cu sites should be occupied by C 2 H 2 after C 2 H 2 pretreatment. The subsequent competition between HCl and C 2 H 2 should promote the catalytic activities of Cu/O−FLP−C 2 H 2 to gradually increase. However, we did not notably observe this trend. In contrast, it could be seen that the performance of acetylene hydrochlorination over Cu/O−FLP−C 2 H 2 significantly decreased, hinting that the catalytic mechanism over Cu/O−FLP−C 2 H 2 should be different from that over Cu/O−FLP−HCl. According to the TGA data ( Figure S13 and Table S1 ), the higher carbon deposition over Cu/O−FLP−C 2 H 2 , 52 compared with that over Cu/O−FLP−HCl, also supported their different catalytic mechanism. To further explore the difference of catalytic mechanism and reaction pathways, the effects of adsorption/activation order of HCl and C 2 H 2 over the optimum Cu− cis −N 2 C 2 Cl−O1 motif on reaction energy barriers were investigated via density functional theory (DFT) calculations. As shown in Figure 5d , when C 2 H 2 was preferentially adsorbed at single-atom Cu center, the reaction energy barrier increased sharply to 1.76 eV compared with the HCl pre-adsorption (0.81eV), suggesting that the HCl pre-activation could accelerate the reaction. In the first steps of the two different pathways, the adsorption energy (E ads ) of active sites for HCl (-0.39 eV) was obviously lower than that for C 2 H 2 (-0.22 eV), which signified an easier adsorption of HCl over the FLP catalytic site, in good accordance with the experimental observation. After that, the preferentially adsorbed HCl would undergo a key activation step, causing the dissociation of H−Cl bond and formation of Cu−Cl δ– /C−O−H δ+ active species. Following this step, C 2 H 2 approached these active species and was polarized under a local micro-electric field induced by the different electronegativity of the formed Cu−Cl δ– and C−O−H δ+ , enhancing the interaction between the H atom of C 2 H 2 and the Cl atom of Cu−Cl δ– . As a result, this largely reduced the energy barrier for the following vinyl chloride formation (i.e., the rate-limiting step) in the HCl activation pathway. Moreover, the generated vinyl chloride over this Cu/O−FLP-HCl desorbed from the Lewis-basic oxygen site with a lower desorption energy compared with that over the Lewis-acidic Cu site of Cu/O−FLP-C 2 H 2 ( Figure 5c and 5d ), thus ensuring the easier regeneration of Cu/O FLP site in in the HCl activation pathway. These endowed Cu/O−FLP-HCl with a more superior catalytic performance compared with Cu/O−FLP-C 2 H 2 , in accordance with the experimental result. In addition, the DFT calculation revealed that the axial Cl atom in the pristine Cu− cis −N 2 C 2 Cl−O1 motif could help to significantly reduce the energy barrier of vinyl chloride formation (i.e., the rate-limiting step) (0.81 eV) compared with the catalytic configuration without axial Cl atom (Cu− cis −N 2 C 2 −O1) (1.13 eV), implying the crucial role of axial Cl in modulating the electronic environment of FLP catalytic site to boost the acetylene hydrochlorination of Cu/O−FLP. Moreover, the existence of axial Cl atom also contributed to the achievement of saturated coordination configuration of Lewis-acidic Cu site during reaction, which hindered the formation of explosive copper acetylide and ensured the intrinsic safety of Cu/O−FLP catalyst. Conclusion In summary, we fabricated a Cu/O-FLP catalyst bearing Cu − cis − N 2 C 2 Cl motif and epoxide group to enhance acetylene hydrochlorination via preferential cleavage of HCl. Theoretical calculation and experimental characterizations revealed that the single atom Cu and epoxide group, acting as Lewis acid-base catalytic sites, synergistically promoted adsorption and dissociation of HCl to form the Cu − Cl δ– and C − O−H δ+ active species. This not only largely enhanced the acetylene adsorption via both upshift of the d-band center and the microelectric-field-induced polar effect stemming from the electronegativity difference between the formed H δ+ and Cl δ– species, but also notably reduced the reaction energy barrier of the subsequent rate-limiting step and the desorption energy of vinyl chloride. As a consequence, Cu/O-FLP exhibited an outstanding acetylene conversion efficiency (59.4%), exceeding the corresponding reference catalysts at the same condition. Meanwhile, the preferential HCl activation ensured the saturated six-coordination configuration of single-atom Cu center without forming explosive copper acetylide, thereby endowing Cu-based single-atom catalyst with intrinsic safety. Declarations Competing Interest The authors declare no competing financial interests. Acknowledgement This work was supported by the National Natural Science Foundation of China (22062021), the Science and Technology Project of Xinjiang Bingtuan supported by Central government (2022BC001), the Opening Project of Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan (KF2019010), the Start-Up Foundation for high-level professionals of Shihezi University (RCZK201932) and research project of Shihezi University (CXFZ202205). References Hutchings, G. and Grady, D. (1985). Hydrochlorination of acetylene: The effect of mercuric chloride concentration on catalyst life. Appl. Catal. 17 , 155–160. 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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-2361952","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":159432758,"identity":"f9c45c53-964c-4369-bf59-fb6fdafbb547","order_by":0,"name":"Chaofeng 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14:06:02","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2361952/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2361952/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":30272227,"identity":"1a74c495-dae8-456c-ae99-835ef950cde0","added_by":"auto","created_at":"2022-12-13 16:37:39","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":340541,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElemental distribution and structural characterizations of Cu\u003c/strong\u003e/\u003cstrong\u003eO\u003c/strong\u003e−\u003cstrong\u003eFLP.\u003c/strong\u003e(a) STEM−HAADF image; (b) TEM image and representative EDS mapping image of C, N, O, Cl and Cu; High resolution XPS spectra of (c) N 1s; (d) O 1s and (e) Cl 2p.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/930d40df4f70830d6b5421ee.png"},{"id":30273080,"identity":"7160be9f-8d3d-4a98-bec9-a45c7cbc8b40","added_by":"auto","created_at":"2022-12-13 16:45:39","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":177493,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProposed local coordination configuration of Cu\u003c/strong\u003e/\u003cstrong\u003eO\u003c/strong\u003e−\u003cstrong\u003eFLP.\u003c/strong\u003e (a) Cu K−edge XANES spectra and various Cu standard materials; (b) FT−EXAFS fitting curves; (c) Fourier transform of the k\u003csup\u003e3\u003c/sup\u003e−weighted χ-EXAFS data, along with references; (d) Wavelet transforms (WT) contour plots; (e) TOF-SIMS high-resolution negative-ion spectra in the m/z =114.5−117.5 (inset: negative CuC\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e–\u003c/sup\u003e and Cl\u003csup\u003e–\u003c/sup\u003e ion images).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/8fa4de326579589f24730830.png"},{"id":30272232,"identity":"3dcad9ca-baea-44ea-940e-ac0cf96800c4","added_by":"auto","created_at":"2022-12-13 16:37:40","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":23479,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCatalytic performance evaluation in acetylene hydrochlorination.\u003c/strong\u003e Cu/O−FLP−HCl catalyst compared with (a) Cu/O−FLP and Cu/O−FLP−C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e; (b) Turnover frequency (TOF) value and vinyl chloride monomer yield at 9 h; (c) N/C, CuCl\u003csub\u003e2\u003c/sub\u003e/AC and ethylenediaminetetraacetic acid (EDTA) poisoning Cu/O−FLP, labeled as Cu/O−FLP (EDTA). (Reaction conditions: T=180 \u003csup\u003eo\u003c/sup\u003eC, GHSV(C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e) = 180/h and feed volume ratio V(HCl)/V(C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e) = 1.15).\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/4c0c9a437b33f8aea5b4bf10.png"},{"id":30273081,"identity":"496a7fd8-11fb-4bbb-9afb-8cc2aa365239","added_by":"auto","created_at":"2022-12-13 16:45:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":261703,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eChemical state and atomic coordination environment of Cu/O−FLP−HCl characterizations:\u003c/strong\u003e (a) O 1s high−resolution XPS spectra of Cu/O−FLP and Cu/O−FLP−HCl; (b) Cu K−edge XANES spectra; (c) Fourier transform of the k\u003csup\u003e3\u003c/sup\u003e−weighted χ−EXAFS data; (d) NH\u003csub\u003e3\u003c/sub\u003e−TPD profiles of Cu/O−FLP and Cu/O−FLP−HCl; (e) Bader charge analysis; (f) Experimental XANES curve in comparison with calculated XANES data of Cu-\u003cem\u003ecis\u003c/em\u003e-N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl-O1 site in Cu/O-FLP sample. Inset: schematic atomic structure of Cu-\u003cem\u003ecis\u003c/em\u003e-N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl-O1 derived from the EXAFS results; Differential charge density analysis of (g) Cu−\u003cem\u003ecis\u003c/em\u003e−C\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eCl−O and (h) Cu−\u003cem\u003e cis\u003c/em\u003e−C\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eCl.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/1cda46275bf9c750b13beb3d.png"},{"id":30272228,"identity":"a9ec0cf1-eb71-46ab-93ee-210fa6345890","added_by":"auto","created_at":"2022-12-13 16:37:39","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":150818,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCatalytic descriptors. \u003c/strong\u003e(a) Electron field distribution of Cu/O−FLP and Cu/O−FLP−HCl; (b) Ultraviolet photo−electron spectroscopy (UPS) spectra; (c) C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e−TPD of N/C−HCl, Cu/O−FLP and Cu/O−FLP−HCl; VCM desorption energy of Cu/O−FLP−C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e and Cu/O−FLP−HCl; (d) Potential energy profiles along the vinyl chloride monomer formation route over Cu−\u003cem\u003ecis\u003c/em\u003e−N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e−O1 and Cu−\u003cem\u003ecis\u003c/em\u003e−N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl−O1 model with HCl and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e pre-activation, respectively. Inset: the main structures of intermediates and transition states over Cu−\u003cem\u003ecis\u003c/em\u003e−N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl−O1−HCl. The white, gray, blue, green, orange and red spheres represent H, C, N, Cl, Cu and O elements, respectively.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/83f0db5482be4f8d58555c98.png"},{"id":30378990,"identity":"c3a05e51-149e-45d4-bd05-bfb061182921","added_by":"auto","created_at":"2022-12-15 15:38:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1243802,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/eb01ed8a-6c9f-4b84-a94c-1e6a3453e2e6.pdf"},{"id":30272231,"identity":"e89ec191-6652-452d-9e83-2353e7df37b3","added_by":"auto","created_at":"2022-12-13 16:37:40","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2487881,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-2361952/v1/137ff6e940636d995a07bd74.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single−atom Cu/O Lewis pair for acetylene hydrochlorination","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAcetylene hydrochlorination represented one of important industrial reactions for producing vinyl chloride monomer, which was widely used for polyvinylchloride (PVC).\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e To date, activated carbon supported mercuric chloride as a common acetylene hydrochlorination catalyst had triggered numerous environmental problems due to high toxicity and easy sublimation. Although various mercury-free catalysts such as noble-metal Au,\u003csup\u003e\u003cspan additionalcitationids=\"CR3 CR4 CR5\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e Pt,\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e Ru,\u003csup\u003e\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e Pd,\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e noble metal alloy and metal-free doped carbon\u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e had been extensively developed, many of these alternatives generally suffered from several limitations, including expensive price, carbon deposition,\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e cationic metal over-reduction\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e and/or leaching.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e By contrast, the atom\u0026thinsp;\u0026minus;\u0026thinsp;dispersed Cu anchored on carbon matrix was recently concerned due to potential activity for acetylene hydrochlorination as well as the maximal atom utilization and high theoretically initial activity.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e Moreover, the electronic configuration and coordination environment/number of carbon-supported single-atom Cu site were facile to be regulated by various doped heteroatoms, including N and P.\u003csup\u003e\u003cspan additionalcitationids=\"CR22 CR23\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e These single-atom Cu catalysts tended to catalyze acetylene hydrochlorination via a critical initial step that the active Cu sites were generally prone to pre-adsorb acetylene, which was followed by the H\u0026thinsp;\u0026minus;\u0026thinsp;Cl bond cleavage to form vinyl chloride. However, the high symmetry of acetylene molecule made the electron cloud of carbon-carbon triple bond (C\u0026thinsp;\u0026equiv;\u0026thinsp;C) difficult to be polarized, compared with the polar H\u0026thinsp;\u0026minus;\u0026thinsp;Cl bond. This probably affected the hydrochlorination performance of catalysts.\u003c/p\u003e \u003cp\u003eIn addition, for most single-atom Cu catalysts that used N or P doped carbon as supports, not all N/P heteroatoms were coordinated with Cu atoms.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e Theoretically, these uncoordinated N/P heteroatoms in the doped carbon supports could be regarded as the solid base due to their electron-rich features. Thus, in the presence of these uncoordinated N or P basic dopants, preferential adsorption of acetylene over the single-atom Cu site immobilized on the N/P\u0026thinsp;\u0026minus;\u0026thinsp;doped carbon possibly resulted in a potential risk of forming copper acetylide, which belonged to hazardous explosive (\u003cb\u003eScheme S1\u003c/b\u003e). Especially, when these single-atom Cu catalysts were applied for acetylene hydrochlorination on a large scale, the explosive risk originating from formation of copper acetylide at high temperature possibly rose. Thus, a reasonable consideration was whether HCl could be preferentially adsorbed, activated and broken into H\u003csup\u003eδ+\u003c/sup\u003e and Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e intermediates at active sites. If possible, this would avoid the risk of producing copper acetylide at Cu site by impeding the direct interaction between Cu and acetylene. Furthermore, owing to the different electronegativity, the formed H\u003csup\u003eδ+\u003c/sup\u003e and Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e were conducive to inducing an extra local electric field around active sites to enhance polarization of electron cloud of C\u0026thinsp;\u0026equiv;\u0026thinsp;C to promote subsequent acetylene hydrochlorination.\u003c/p\u003e \u003cp\u003eThe recently proposed frustrated Lewis acid\u0026thinsp;\u0026minus;\u0026thinsp;base pair (FLP) showed great potential in activating and cleaving chemical bonds of various gaseous molecules, including H\u003csub\u003e2,\u003c/sub\u003e\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e N\u003csub\u003e2,\u003c/sub\u003e\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e and CO\u003csub\u003e2\u003c/sub\u003e.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e The heterolytic cleavage of H\u0026ndash;Cl bond would produce H\u003csup\u003eδ+\u003c/sup\u003e and Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e species, which belong to Br\u0026oslash;nsted acid and Lewis base, respectively. In principle, dissociating the H\u0026ndash;Cl bond was probably achieved by fabricating the single\u0026thinsp;\u0026minus;\u0026thinsp;atom Cu/O pair as FLP site. This would give rise to active Cu\u0026thinsp;\u0026minus;\u0026thinsp;Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e and O\u0026thinsp;\u0026minus;\u0026thinsp;H\u003csup\u003eδ+\u003c/sup\u003e species at this atom-dispersed Cu/O FLP site, which contributed to inducing a polarization filed because of the electronegativity difference between H\u003csup\u003eδ+\u003c/sup\u003e and Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e to promote subsequent acetylene hydrochlorination. However, preferential cleavage of H\u0026ndash;Cl bond over the single\u0026thinsp;\u0026minus;\u0026thinsp;atom Cu/O FLP site to enhance acetylene hydrochlorination and avoid forming copper acetylide at Cu sites was seldom reported.\u003c/p\u003e \u003cp\u003eHerein, we constructed a single\u0026thinsp;\u0026minus;\u0026thinsp;atom Cu/O\u0026thinsp;\u0026minus;\u0026thinsp;FLP catalyst consisting of the atom\u0026thinsp;\u0026minus;\u0026thinsp;dispersed Cu\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ecis\u003c/em\u003e\u0026thinsp;\u0026minus;\u0026thinsp;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl center (i.e., Cu coordinated with two N and two C atoms in the cis\u0026thinsp;\u0026minus;\u0026thinsp;configuration and an axial Cl atom) and functional epoxide (C\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;C) group, which acted as FLP sites to activate and cleave H\u0026thinsp;\u0026minus;\u0026thinsp;Cl bond, giving rise to the Cu\u0026thinsp;\u0026minus;\u0026thinsp;Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e and C\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;H\u003csup\u003eδ+\u003c/sup\u003e species at catalytic sites during HCl pre\u0026thinsp;\u0026minus;\u0026thinsp;activation. This both upshifted the d-band center of catalyst toward Fermi level and induced an extra local electric field to polarize the electron cloud of acetylene, thereby promoting the enrichment and adsorption of acetylene. Meanwhile, preferential dissociation of HCl reduced the energy barrier of rate-limiting step and ensured the easier desorption of formed vinyl chloride over the Lewis-basic oxygen atom site, rather than Lewis-acidic Cu site. As a result, the HCl\u0026thinsp;\u0026minus;\u0026thinsp;activated Cu/O\u0026thinsp;\u0026minus;\u0026thinsp;FLP presented an enhanced catalytic activity for acetylene hydrochlorination. In addition, the newly formed Cu\u0026thinsp;\u0026minus;\u0026thinsp;Cl\u003csup\u003eδ\u0026minus;\u003c/sup\u003e could impeded the direct interaction between Cu and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e, improving the intrinsic safety by avoiding forming explosive copper acetylide.\u003c/p\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003eTo fabricate frustrated single\u0026minus;atom Cu/O Lewis pair site over doped carbon support, we chose imidazolium ionic liquid, CuCl\u003csub\u003e2\u003c/sub\u003e and glucose as precursors. After hydrothermal reaction, pyrolysis at 600 \u003csup\u003eo\u003c/sup\u003eC and nitric acid treatment, the catalyst with single\u0026minus;atom Cu/O Lewis pair site was obtained (See more synthesis details in Experimental Section of Supporting Information) and labelled as Cu/O\u0026minus;FLP. According to\u0026nbsp;X\u0026minus;ray diffraction (XRD) analysis, no obvious Cu\u0026minus;related crystalline peaks was observed in\u0026nbsp;Cu/O\u0026minus;FLP, except the graphitic carbon peaks (\u003cstrong\u003eFigure S1\u003c/strong\u003e), indicating that Cu was dispersed in the atomic form or small nanoparticles/clusters. To further confirm the existing form of Cu, we used spherical aberration corrected high\u0026minus;angle annular dark-field scanning\u0026nbsp;transmission electron microscope\u0026nbsp;(HAADF\u0026minus;STEM) to observe the morphology of\u0026nbsp;Cu/O\u0026minus;FLP. \u003cstrong\u003eFigure 1a\u003c/strong\u003e showed that numerous isolated Cu atoms\u0026nbsp;were anchored in the doped carbon matrix, agreeing well with the XRD result. The energy-dispersive X\u0026minus;ray spectroscopy (EDS) mapping displayed that Cu/O\u0026minus;FLP contained C, N, O, Cl and Cu elements, which were uniformly distributed in sample (\u003cstrong\u003eFigure 1b\u003c/strong\u003e). The corresponding Cu content was determined to be 4.1wt.% according to inductively coupled plasma optical emission spectrometer (ICP\u0026minus;OES) measurement. Moreover, the surface area (631 m\u003csup\u003e2\u003c/sup\u003e/g) and micro-mesoporous structure (\u0026gt; 1 nm) were determined by Brunauer\u0026minus;Emmett\u0026minus;Teller (BET) measurements\u0026nbsp;(\u003cstrong\u003eTable S1 and Figure S2\u003c/strong\u003e),\u0026nbsp;which was expected to promote the exposure of single\u0026minus;atom Cu/O\u0026nbsp;FLP\u0026nbsp;site and fast mass transfer of HCl and\u0026nbsp;acetylene\u0026nbsp;to catalytic sites for enhancing\u0026nbsp;hydrochlorination activity of catalyst,\u0026nbsp;respectively.\u003c/p\u003e\n\u003cp\u003eThe chemical state of Cu in Cu/O\u0026minus;FLP was investigated using X\u0026minus;ray photoelectron spectroscopy (XPS). The Cu 2p XPS spectrum (\u003cstrong\u003eFigure S3\u003c/strong\u003e) discovered that the dominant oxidation state of Cu located in the region of +1 and +2, similar to many reported Cu single\u0026minus;atom carbonaceous materials.\u003csup\u003e30-33\u003c/sup\u003e According to N 1s XPS spectrum (\u003cstrong\u003eFigure 1c\u003c/strong\u003e), Cu-coordinated N (Cu\u0026minus;N\u003csub\u003ex\u003c/sub\u003e) species was obviously observed in Cu/O\u0026minus;FLP, except the pyrrolic, pyridinic, graphitic and oxidative N.\u003csup\u003e34-36\u003c/sup\u003e In the O 1s XPS spectrum (\u003cstrong\u003eFigure 1d\u003c/strong\u003e), C\u0026minus;OH, C\u0026minus;O\u0026minus;C and C=O were presented in Cu/O\u0026minus;FLP,\u003csup\u003e37\u003c/sup\u003e which was also supported by Fourier transform infrared spectroscopy (FT\u0026minus;IR) (\u003cstrong\u003eFigure S4\u003c/strong\u003e). Meanwhile, no Cu\u0026minus;O bond was found in O 1s XPS spectrum,\u003csup\u003e38\u003c/sup\u003e excluding the existence of Cu\u0026minus;O coordination bond. The Cl 2p XPS spectrum revealed that there existed Cu\u0026minus;Cl bond in Cu/O\u0026minus;FLP (\u003cstrong\u003eFigure 1e\u003c/strong\u003e).\u003csup\u003e39,40\u003c/sup\u003e These XPS results indicated that the first coordination shell of atom\u0026minus;dispersed Cu sites contained N and Cl atoms.\u003c/p\u003e\n\u003cp\u003eTo deeply disclose the local coordination environment of single-atom Cu in Cu/O\u0026minus;FLP, X\u0026minus;ray absorption near-edge structure (XANES) and extended X\u0026minus;ray absorption fine structure (EXAFS) spectroscopic measurements were conducted, and Cu foil, copper oxide (CuO), cuprous oxide (Cu\u003csub\u003e2\u003c/sub\u003eO), cupric chloride (CuCl\u003csub\u003e2\u003c/sub\u003e) and copper phthalocyanine (CuPc) were used as reference. As depicted in\u0026nbsp;Cu K\u0026minus;edge XANES spectrum (\u003cstrong\u003eFigure 2a\u003c/strong\u003e), the rising absorption edge of\u0026nbsp;Cu/O\u0026minus;FLP\u0026nbsp;was situated between those of Cu\u003csub\u003e2\u003c/sub\u003eO and CuO, indicating that the average valence state of single-atom Cu\u003csup\u003e\u0026delta;+\u0026nbsp;\u003c/sup\u003ewas 1 \u0026lt; \u0026delta; \u0026lt; 2, in consistent well with the Cu 2p XPS result. Through k\u003csup\u003e3\u003c/sup\u003e\u0026minus;weighted Fourier\u0026minus;transform, the first coordination shell of atom\u0026minus;dispersed Cu in\u0026nbsp;Cu/O\u0026minus;FLP\u0026nbsp;appeared at 1.50 and 1.90 \u0026Aring; in the R space EXAFS spectra, which corresponded to the Cu\u0026minus;C/N/O and Cu\u0026minus;Cl bonds, respectively (\u003cstrong\u003eFigure 2b\u003c/strong\u003e). The Cu\u0026minus;O bond was excluded according to the O 1s XPS spectrum (\u003cstrong\u003eFigure 1d\u003c/strong\u003e). Nevertheless, it was still difficult to distinguish Cu\u0026minus;N and Cu\u0026minus;C bonds from the R space EXAFS spectrum, due to their similar bond lengths. In addition, compared with the standard Cu foil,\u0026nbsp;no\u0026nbsp;obvious Cu\u0026minus;Cu characteristic peaks was found in\u0026nbsp;Cu/O\u0026minus;FLP\u0026nbsp;(\u003cstrong\u003eFigure 2c\u003c/strong\u003e). In the wavelet transform (WT) contour plots, the maximum intensity of\u0026nbsp;Cu/O\u0026minus;FLP\u0026nbsp;located at 4.6 \u0026Aring;\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003eobviously distinct from that of Cu foil, further confirming the atomic dispersion of Cu species in\u0026nbsp;Cu/O\u0026minus;FLP\u0026nbsp;(\u003cstrong\u003eFigure 2d\u003c/strong\u003e). The further fitting result disclosed that the coordination number of single\u0026minus;atom Cu approached five, which consisted of four N/C atoms and one Cl atom (\u003cstrong\u003eTable S2\u003c/strong\u003e), indicating that the Cu atoms were mainly dispersed on the doped carbon matrix with the Cu\u0026minus;N\u003csub\u003ex\u003c/sub\u003eC\u003csub\u003e4-x\u003c/sub\u003eCl (1\u0026nbsp;\u0026le;\u0026nbsp;X\u0026nbsp;\u0026le; 4) moiety.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo further determine the most probable local coordination configuration of Cu atom, we performed time\u0026minus;of\u0026minus;flight secondary ion mass spectrometry (TOF\u0026minus;SIMS) measurement.\u003csup\u003e41\u003c/sup\u003e As shown in \u003cstrong\u003eFigure 2e\u003c/strong\u003e, the negative fragment ion peaks in the mass region m/z = 114.5\u0026minus;117.5 could be obvious detected during Bi\u003csup\u003e3+\u003c/sup\u003e ions beam sputtering on Cu/O\u0026minus;FLP, which corresponded to the Cu and Cu isotope of CuC\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e units. The TOF\u0026minus;SIMS negative ion imaging also directly observed the detected CuC\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e fragments. Moreover, we found that the Cl negative ions presented an obvious enrichment in the position with abundant CuC\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e fragments. Combining the TOF\u0026minus;SIMS, EXAFS and XPS results, it could be inferred that the Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl configuration probably existed in the matrix of Cu/O\u0026minus;FLP. Meanwhile, \u003cstrong\u003eFigure 2a\u003c/strong\u003e revealed that the intensity of the 1s\u0026rarr;4p\u003csub\u003ez\u003c/sub\u003e transition peak (8985eV)\u003csup\u003e42,43\u003c/sup\u003e in the Cu K\u0026minus;edge XANES spectrum of Cu/O-FLP drastically decreased compared with that in CuPc (\u003cstrong\u003eFigure 2a\u003c/strong\u003e), indicating the low symmetry of\u0026nbsp;Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl motif. This hinted the Cu atom in Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl moiety of Cu/O\u0026minus;FLP probably coordinated with two C and two N atoms in the cis\u0026minus;configuration, which would be discussed in the following part.\u003c/p\u003e\n\u003cp\u003eNext, we evaluated the acetylene hydrochlorination performance of as\u0026minus;synthesized Cu/O\u0026minus;FLP. The control samples, including N\u0026minus;free active carbon\u0026minus;supported CuCl\u003csub\u003e2\u003c/sub\u003e (CuCl\u003csub\u003e2\u003c/sub\u003e/AC) and Cu\u0026minus;free N\u0026minus;doped carbon (N/C) were chosen as references (See Experimental Section in Supporting Information). Interestingly, it was found that HCl pre-activation could significantly boost the acetylene hydrochlorination performance of Cu/O\u0026minus;FLP compared with C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e pre\u0026minus;activation and unactivated samples (\u003cstrong\u003eFigure 3a\u003c/strong\u003e, HCl and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u0026minus;pretreated Cu/O\u0026minus;FLP were denoted as Cu/O\u0026minus;FLP\u0026minus;HCl and Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e, respectively, see more details of pre\u0026minus;activation treatment in Supporting Information). The conversion efficiency of acetylene over Cu/O\u0026minus;FLP\u0026minus;HCl reached 59.4 % during 9 h operation (\u003cstrong\u003eFigure 3a\u003c/strong\u003e), which obviously exceeded those of Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e (33.4%) and the untreated Cu/O\u0026minus;FLP (46.05%), implying that HCl pretreatment probably modulate the microstructure of active sites to alter the catalytic pathway. These catalysts showed ~100% selectivity for vinyl chloride under the same condition (\u003cstrong\u003eFigure S5\u003c/strong\u003e), but the yield and turnover frequency of Cu/O\u0026minus;FLP\u0026minus;HCl were significantly superior to those of Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e catalyst (\u003cstrong\u003eFigure 3b\u003c/strong\u003e). Furthermore, Cu/O\u0026minus;FLP\u0026minus;HCl also presented a higher acetylene conversion efficiency than CuCl\u003csub\u003e2\u003c/sub\u003e/AC (25.4 %) and N/C (1.76 %) (\u003cstrong\u003eFigure 3c\u003c/strong\u003e). Considering that CuCl\u003csub\u003e2\u003c/sub\u003e/AC and N/C did not contain N dopant and Cu atom, respectively, the above catalytic data directly demonstrated the crucial role of N\u0026minus;coordinated single\u0026minus;atom Cu center of Cu/O\u0026minus;FLP in efficiently catalyzing acetylene hydrochlorination to form vinyl chloride. To further confirm whether the Lewis-acidic Cu in local\u0026nbsp;Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026nbsp;configuration\u0026nbsp;was the active site for acetylene hydrochlorination, we used ethylenediaminetetraacetic acid (EDTA) as chelating agent to remove Cu ions of Cu/O\u0026minus;FLP by stirring them in aqueous solution. After 24 h, the mixture was centrifugated. UV\u0026minus;Vis spectrum of the supernatant displayed an obvious adsorption at 271 nm (\u003cstrong\u003eFigure S6\u003c/strong\u003e), which was assigned to EDTA\u0026minus;Cu complex, indicating successful removal of Cu ions.\u003csup\u003e44\u003c/sup\u003e The corresponding performance measurement showed that removal of Cu ions resulted in a 22.1 % decrement of the acetylene conversion efficiency after 9 h duration, suggesting the Lewis-acidic Cu in the localized Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026nbsp;configuration\u0026nbsp;was the active site of Cu/O\u0026minus;FLP for acetylene hydrochlorination (\u003cstrong\u003eFigure 3d\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003eTo explore why HCl pre\u0026minus;activation enhanced the catalytic\u0026nbsp;performance of Cu/O\u0026minus;FLP compared with C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e pre-activation, temperature programmed desorption (TPD) experiments were employed to investigate the different absorption strength of Cu/O\u0026minus;FLP for HCl and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e. As shown in \u003cstrong\u003eFigure S7\u003c/strong\u003e, the HCl desorption occurred at a higher temperature, compared with the C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e desorption. This manifested the stronger bonding strength of Cu/O\u0026minus;FLP for HCl, signifying that the\u0026nbsp;active\u0026nbsp;site probably tended to preferentially adsorb and activate HCl during acetylene hydrochlorination.\u003csup\u003e45\u003c/sup\u003e To identify the crucial role of oxygen atom in doped carbon matrix during HCl pre-activation, the O 1s XPS spectra of Cu/O\u0026minus;FLP before and after HCl pre-treatment were collected. \u003cstrong\u003eFigure 4a\u003c/strong\u003e disclosed that after HCl pre\u0026minus;activation, the content of C\u0026minus;O\u0026minus;C obviously decreased, which was accompanied with the increment of C\u0026minus;OH content. This implied that the C\u0026minus;O\u0026minus;C was probably the epoxide group and the H\u0026minus;Cl bond could be ruptured by protonating and cleaving the epoxide group via a ring-opening reaction to form the C\u0026minus;OH bond. In this sense, the electron\u0026minus;rich oxygen atom in the epoxide group played the role of Lewis basic site during the H\u0026minus;Cl cleavage, which accepted the proton of HCl to produce C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eOn the other hand, the single\u0026minus;atom Cu was demonstrated to be the catalytic site according to the above EDTA\u0026minus;poisoning experiment (\u003cstrong\u003eFigure 3d\u003c/strong\u003e). In the\u0026nbsp;Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026nbsp;site of Cu/O\u0026minus;FLP, the single\u0026minus;atom Cu essentially belonged to Lewis acid due to its positive chemical valance. The Cl atom of HCl possessed more negative charge because of its stronger electronegativity. In this regard, the H\u003csup\u003e\u0026delta;+\u003c/sup\u003e and Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e atoms in HCl could be seen as Br\u0026oslash;nsted acid and Lewis base, respectively. Given that the O atom (Lewis base) in the C\u0026minus;O\u0026minus;C group interacted with HCl and accepted its H\u003csup\u003e\u0026delta;+\u003c/sup\u003e atom (Br\u0026oslash;nsted acid), we thus considered that whether the Cu atom (Lewis acid) in the\u0026nbsp;Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026nbsp;site probably accepted the Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e atom (Lewis base) of HCl to form the extra Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u0026nbsp;\u003c/sup\u003eand promoted the scission of H\u0026minus;Cl bond by cooperating with the O atom (Lewis base) of the C\u0026minus;O\u0026minus;C group during HCl pre\u0026minus;activation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo evidence the formation of extra Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e during HCl pre-activation, XANES and EXAFS spectroscopic measurements were conducted. According to the Cu K\u0026minus;edge XANES spectra (\u003cstrong\u003eFigure 4b\u003c/strong\u003e), the\u0026nbsp;Cu/O\u0026minus;FLP\u0026minus;HCl showed an enhanced white line intensity, hinting that the Cu atom in\u0026nbsp;Cu/O\u0026minus;FLP\u0026minus;HCl possessed a higher oxidation\u0026nbsp;state compared with the pristine Cu/O\u0026minus;FLP in correspondence with the Cu 2p XPS result (\u003cstrong\u003eFigure S8\u003c/strong\u003e).\u003csup\u003e46\u003c/sup\u003e This suggested the coordination environment of Lewis-acidic Cu site had been altered after HCl pre\u0026minus;activation, which was also supported by the corresponding R space EXAFS spectrum. As depicted in \u003cstrong\u003eFigure 4c\u003c/strong\u003e,\u0026nbsp;the Cu in Cu/O\u0026minus;FLP\u0026minus;HCl still maintained the formation of atomic dispersion, and\u0026nbsp;the main peak intensity of\u0026nbsp;Cu/O\u0026minus;FLP\u0026minus;HCl\u0026nbsp;was obviously higher than that of\u0026nbsp;the pristine Cu/O\u0026minus;FLP, indicating that the coordination number of atom\u0026minus;dispersed Cu in Cu/O\u0026minus;FLP\u0026minus;HCl increased.\u003csup\u003e47\u003c/sup\u003e The fitting data further provided experimental proof, which displayed that the single\u0026minus;atom Cu in Cu/O\u0026minus;FLP\u0026minus;HCl was connected by six atoms, involving two N, two C and two Cl atoms (\u003cstrong\u003eTable S2\u003c/strong\u003e).\u0026nbsp;Compared with\u0026nbsp;Cu/O\u0026minus;FLP, the extra increase of Cl atom at\u0026nbsp;the first coordination shell\u0026nbsp;of single-atom Cu in Cu/O\u0026minus;FLP-HCl strongly demonstrated the formation of extra Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e during HCl pre\u0026minus;activation.\u003c/p\u003e\n\u003cp\u003eIn theory, introducing the extra Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e bond into the original Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl site by cleaving H\u0026minus;Cl bond would lead to the saturated coordination configuration of single\u0026minus;atom Cu (i.e., Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e). We thus used NH\u003csub\u003e3\u003c/sub\u003e\u0026minus;TPD to further verify the formation of extra Cu\u0026minus;Cl bond in Cu/O\u0026minus;FLP\u0026minus;HCl. As shown in \u003cstrong\u003eFigure 4d\u003c/strong\u003e, the pristine Cu/O\u0026minus;FLP exhibited two typical desorption peaks at 112 \u003csup\u003eo\u003c/sup\u003eC and 294 \u003csup\u003eo\u003c/sup\u003eC before HCl pre\u0026minus;activation, corresponding to Br\u0026oslash;nsted acid site and Lewis acid site, respectively. Once pre\u0026minus;activated by HCl, the NH\u003csub\u003e3\u003c/sub\u003e desorption peak of the Lewis-acidic Cu site almost disappeared. This directly confirmed the formation of extra Cu\u0026minus;Cl bond again, which resulted in a saturated coordination configuration of single\u0026minus;atom Cu site, making NH\u003csub\u003e3\u003c/sub\u003e difficult to be adsorbed at Lewis-acidic Cu site. Such a result was also confirmed by the in\u0026minus;situ IR spectra of adsorbed pyridine detected at 350 \u003csup\u003eo\u003c/sup\u003eC (\u003cstrong\u003eFigure S9\u003c/strong\u003e). It displayed that the pyridine adsorption peak of Lewis-acidic Cu site in the Cu/O\u0026minus;FLP\u0026minus;HCl drastically decreased compared with Cu/O\u0026minus;FLP, which resulted from the site\u0026minus;blocking effect of extra Cl atom at the atomic Cu center. Moreover, according to the NH\u003csub\u003e3\u003c/sub\u003e\u0026minus;TPD result, it can be found that the desorption peak intensity of Br\u0026oslash;nsted acid site (112 \u003csup\u003eo\u003c/sup\u003eC) obviously increased, manifesting the new generation of C\u0026minus;OH group with\u0026nbsp;Br\u0026oslash;nsted acidity (O\u0026minus;H\u003csup\u003e\u0026delta;+\u003c/sup\u003e) during HCl pre\u0026minus;activation, which was expected to facilitate the protonation step of C\u0026equiv;C bond of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e. On the basis of all the above\u0026nbsp;data, it could be concluded that the oxygen atom of C\u0026minus;O\u0026minus;C group and single\u0026minus;atom Cu played the roles of frustrated Cu/O Lewis acid\u0026minus;base pair, which corporately participated in the HCl activation and broke H\u0026minus;Cl bond to form\u0026nbsp;C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u003c/sup\u003e and Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e intermediates at Cu/O FLP active sites. More importantly, the H\u0026minus;Cl bond cleavage provided the extra Cl atom for Cu and endowed single\u0026minus;atom Cu with the saturated coordination configuration at\u0026nbsp;its first coordination shell\u0026nbsp;(i.e., Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e),\u0026nbsp;which effectively impeded the direct interaction between Cu and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e, avoiding a potential risk of forming explosive copper acetylide.\u003c/p\u003e\n\u003cp\u003eAccording to the above discussions, the atom\u0026minus;dispersed Cu center in Cu/O\u0026minus;FLP catalyst formed the stable six\u0026minus;coordination structure after dissociating HCl. That is, the Cu site coordinated with two C, two N and two Cl atoms. Theoretically, the single\u0026minus;atom Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl coordination center in the pristine Cu/O\u0026minus;FLP catalyst possessed two possible conformations, i.e., Cu coordinated with two N and two C atoms in the cis\u0026minus;configuration (Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl) or Cu connected by two N and two C atoms in the trans\u0026minus;configuration (Cu\u0026minus;\u003cem\u003etrans\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl). In the two kinds of possible conformations, we herein considered four different structures (i.e., Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1, Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O2, Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O3 and Cu\u0026minus;\u003cem\u003etrans\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O4) according to the different location between the O atom of epoxide (C\u0026minus;O\u0026minus;C) group and the Cu\u0026minus;N (or Cu\u0026minus;C) bond (\u003cstrong\u003eFigure S10\u003c/strong\u003e). To ascertain the optimum Cu/O FLP site structure that could stably dissociate the H\u0026minus;Cl bond, Bader charge analysis was performed to estimate the oxidation states of Cu in these four different structures.\u003csup\u003e48\u003c/sup\u003e \u003cstrong\u003eFigure 4e\u003c/strong\u003e showed that the calculated valence states of Cu in Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 and Cu\u0026minus;\u003cem\u003etrans\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O4 configurations were obviously higher than those in Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O2 and Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O3 configurations. In theory, the higher valence state of single\u0026minus;atom Cu, which signified a more electron\u0026minus;deficient characteristic, would be beneficial to stabilizing the Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e atom that originated from the HCl dissociation by enhancing the Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e bond strength. In order to verify this, the\u0026nbsp;structural stability analysis\u0026nbsp;was further conducted according to theoretical DFT canulations. As displayed in \u003cstrong\u003eFigure S10\u003c/strong\u003e, only Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 was capable to cleave H\u0026minus;Cl bond to form the stable six\u0026minus;coordination configuration at\u0026nbsp;its first coordination shell (i.e., Cu\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e), matching well with the experimental result. In addition, the theoretical valance of Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 obtained by Bader charge analysis approached the Cu 2p XPS calculated data (\u003cstrong\u003eFigure S8\u003c/strong\u003e). However, another three single\u0026minus;atom Cu/O FLP configurations were well excluded, because they could not either exist stably or form the stable six\u0026minus;coordination configuration at Cu center after HCl pre-activation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo further confirm this optimum Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 configuration, we performed XANES modeling based on Finite Difference Method Near Edge Structure (FDMNES) calculation, which was usually reported to identify the metal single\u0026minus;atom coordination structure of M\u0026minus;N\u0026minus;C.\u003csup\u003e49\u003c/sup\u003e \u003cstrong\u003eFigure 4f\u003c/strong\u003e showed that the experimental simulation spectra presented a relatively satisfactory agreement on the basis of the Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 model. Moreover, the corresponding differential charge density analysis discovered that when the\u0026nbsp;epoxide\u0026nbsp;group existed in the vicinal location of Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl center, the charge state of single\u0026minus;atom Cu became more positive due to the inductive effect of oxygen atom in functional\u0026nbsp;epoxide\u0026nbsp;group, in agreement with the previous report\u003csup\u003e37\u003c/sup\u003e (\u003cstrong\u003eFigure 4g\u0026nbsp;\u003c/strong\u003eand\u003cstrong\u003e\u0026nbsp;Figure 4h\u003c/strong\u003e). This also supported the experimental observation that the extra Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e atom originating from the HCl dissociation could be stabilized by the more electron\u0026minus;deficient Cu via formation of the Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e bond.\u0026nbsp;Meanwhile, once the electron of\u0026nbsp;single-atom Cu site flowed to the high-electronegative O atom of epoxide\u0026nbsp;group, this would give rise to the more electron-rich environment around the O atom, which helped the epoxide\u0026nbsp;group to\u0026nbsp;accept the H\u003csup\u003e\u0026delta;+\u003c/sup\u003e atom of HCl via the ring-opening reaction. As a result, the electron-rich epoxide\u0026nbsp;group\u0026nbsp;cooperated with the more positive charged Cu atom to promote the key step of H\u0026minus;Cl adsorption and dissociation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll of these data indicated that the atom\u0026minus;dispersed Cu in Cu/O\u0026minus;FLP catalyst was probably\u0026nbsp;incorporated in doped porous carbon matrix via a\u0026nbsp;local configuration of Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl, and the\u0026nbsp;epoxide\u0026nbsp;group was probably situated in the vicinal location of Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl center. Moreover, such a vicinal oxygen atom in the\u0026nbsp;epoxide\u0026nbsp;group not only modulated the electron\u0026minus;deficient state of Cu center but also paired with atom\u0026minus;dispersed Cu to work as frustrated Cu/O Lewis acid\u0026minus;base pair, which activated HCl and broke H\u0026minus;Cl bond to form stable C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u003c/sup\u003e and Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e intermediates for acetylene hydrochlorination.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe obvious electronegativity difference arising from the newly formed Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e and H\u003csup\u003e\u0026delta;+\u003c/sup\u003e at the Cu/O FLP site tended to induce a local polarized electric field, which would contribute to enhancing the electron cloud polarization of C\u0026equiv;C in the highly symmetric acetylene molecule (\u003cstrong\u003eFigure 5a\u003c/strong\u003e). This probably promote the C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e enrichment and adsorption by improving the dipolar interaction between C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e and active Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e/C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u0026nbsp;\u003c/sup\u003especies, thereby facilitating\u0026nbsp;acetylene hydrochlorination. To experimentally verify this, we destructed Cu/O FLP site by choosing EDTA to remove Cu and obtained Cu/O\u0026minus;FLP(EDTA) catalyst, which was further pretreated by HCl to produce Cu/O\u0026minus;FLP(EDTA) \u0026minus;HCl. The subsequent TPD result revealed that the desorption amount of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e over Cu/O\u0026minus;FLP(EDTA) \u0026minus;HCl significantly decreased compared with that over Cu/O\u0026minus;FLP\u0026minus;HCl (\u003cstrong\u003eFigure S11\u003c/strong\u003e), which was attributed to the difficult cleavage of the H\u0026minus;Cl bond because of destruction of FLP site, making the extra local electric field unformed. As a result, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e was difficult to be polarized, thereby causing a poor C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e adsorption. This further supported that\u0026nbsp;dissociation of\u0026nbsp;HCl over Cu/O FLP site could induced a local polarized electric field to promote C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e adsorption and enrichment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUltraviolet photo\u0026minus;electron spectroscopy (UPS) was also employed to investigate the d-band center of catalyst,\u003csup\u003e50,51\u003c/sup\u003e which could act as an indicator to indicate the interaction strength between catalyst and adsorbate. \u003cstrong\u003eFigure 5b\u0026nbsp;\u003c/strong\u003eillustrated that the d\u0026minus;band center of Cu/O\u0026minus;FLP\u0026minus;HCl obviously upshifted toward Fermi level compared with Cu/O\u0026minus;FLP, leading to a higher desorption peak intensity of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e over Cu/O\u0026minus;FLP-HCl (\u003cstrong\u003eFigure 5c\u003c/strong\u003e), which supported the above result. In addition, the desorption energy of formed vinyl chloride over Cu/O\u0026minus;FLP\u0026minus;HCl was obviously lower than that over Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e (\u003cstrong\u003eFigure 5c\u003c/strong\u003e). These implied that preferential cleavage of HCl into active Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e/C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u0026nbsp;\u003c/sup\u003especies promoted the adsorption and enrichment of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e by the electric-field-induced dipolar interaction and upshifting the d-band center of catalyst and the desorption of vinyl chloride. Moreover, once vinyl chloride was formed, the local polarized electric field would sharply decrease (\u003cstrong\u003eFigure 5a\u003c/strong\u003e), due to the disappearance of active Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e and H\u003csup\u003e\u0026delta;+\u003c/sup\u003e species at\u0026nbsp;Cu/O FLP\u0026nbsp;site. As a result, the vinyl chloride product rapidly desorbed from the catalytic site, thereby regenerating the Cu/O Lewis pair center.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSimilar to Cu/O\u0026minus;FLP\u0026minus;HCl, the\u0026nbsp;R space EXAFS spectrum of\u0026nbsp;Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e also exhibited an obvious enhanced main peak intensity compared with that of the original\u0026nbsp;Cu/O\u0026minus;FLP (\u003cstrong\u003eFigure S12\u003c/strong\u003e), which was attributed to the adsorption of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e, thereby increasing the coordination number of single\u0026minus;atom Cu site. However, the Cu\u0026nbsp;K\u0026minus;edge\u0026nbsp;XANES and Cu 2p XPS spectra showed that the valance of Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e was significantly lower than that of Cu/O\u0026minus;FLP\u0026minus;HCl, but higher than that in the pristine Cu/O\u0026minus;FLP (\u003cstrong\u003eFigure S8\u003c/strong\u003e). Such a result indicated that the interaction between C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e and Cu was poorer than that between HCl and Cu, coinciding with the TPD data (\u003cstrong\u003eFigure S7\u003c/strong\u003e). This promoted HCl to better compete with C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e for the catalytic site of Cu/O\u0026minus;FLP, which could explain why the pristine Cu/O\u0026minus;FLP presented an increased activity compared with Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e during acetylene hydrochlorination (\u003cstrong\u003eFigure 3a\u003c/strong\u003e). Based on\u0026nbsp;R space EXAFS spectrum, the catalytic Cu sites should be occupied by C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e after C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e pretreatment. The subsequent competition between HCl and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e should promote the catalytic activities of Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e to gradually increase. However, we did not notably observe this trend. In contrast, it could be seen that the performance of acetylene hydrochlorination over Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e significantly decreased, hinting that the catalytic mechanism over Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e should be different from that over Cu/O\u0026minus;FLP\u0026minus;HCl. According to the TGA data (\u003cstrong\u003eFigure S13\u003c/strong\u003e and\u003cstrong\u003e\u0026nbsp;Table S1\u003c/strong\u003e), the higher carbon deposition over Cu/O\u0026minus;FLP\u0026minus;C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e,\u003csup\u003e52\u003c/sup\u003e compared with that over Cu/O\u0026minus;FLP\u0026minus;HCl, also supported their different catalytic mechanism.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo further explore the difference of catalytic mechanism and reaction pathways, the effects of adsorption/activation order of HCl and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e over the optimum Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 motif on reaction energy barriers were investigated via density functional theory (DFT) calculations. As shown in \u003cstrong\u003eFigure 5d\u003c/strong\u003e, when C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e was preferentially adsorbed at single-atom Cu center, the reaction energy barrier increased sharply to 1.76 eV compared with the HCl pre-adsorption (0.81eV), suggesting that the HCl pre-activation could accelerate the reaction. In the first steps of the two different pathways, the adsorption energy (E\u003csub\u003eads\u003c/sub\u003e) of active sites for HCl (-0.39 eV) was obviously lower than that for C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e (-0.22 eV), which signified an easier adsorption of HCl over the FLP catalytic site, in good accordance with the experimental observation. After that, the preferentially adsorbed HCl would undergo a key activation step, causing the dissociation of H\u0026minus;Cl bond and formation of Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e/C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u0026nbsp;\u003c/sup\u003eactive species. Following this step, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e approached these active species and was polarized under a local micro-electric field induced by the different electronegativity of the formed Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u0026nbsp;\u003c/sup\u003eand C\u0026minus;O\u0026minus;H\u003csup\u003e\u0026delta;+\u003c/sup\u003e, enhancing the interaction between the H atom of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e and the Cl atom of Cu\u0026minus;Cl\u003csup\u003e\u0026delta;\u0026ndash;\u003c/sup\u003e. As a result, this largely reduced the energy barrier for the following vinyl chloride formation (i.e., the rate-limiting step) in the HCl activation pathway. Moreover, the generated vinyl chloride over this Cu/O\u0026minus;FLP-HCl desorbed from the Lewis-basic oxygen site with a lower desorption energy compared with that over the Lewis-acidic Cu site of Cu/O\u0026minus;FLP-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e (\u003cstrong\u003eFigure 5c\u003c/strong\u003e and \u003cstrong\u003e5d\u003c/strong\u003e), thus ensuring the easier regeneration of Cu/O FLP site in in the HCl activation pathway. These endowed Cu/O\u0026minus;FLP-HCl with a more superior catalytic performance compared with Cu/O\u0026minus;FLP-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e, in accordance with the experimental result.\u003c/p\u003e\n\u003cp\u003eIn addition, the DFT calculation revealed that the axial Cl atom in the pristine Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl\u0026minus;O1 motif could help to significantly reduce the energy barrier of vinyl chloride formation (i.e., the rate-limiting step) (0.81 eV) compared with the catalytic configuration without axial Cl atom (Cu\u0026minus;\u003cem\u003ecis\u003c/em\u003e\u0026minus;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e\u0026minus;O1) (1.13 eV), implying the crucial role of axial Cl in modulating the electronic environment of FLP catalytic site to boost the acetylene hydrochlorination of Cu/O\u0026minus;FLP. Moreover, the existence of axial Cl atom also contributed to the achievement of saturated coordination configuration of Lewis-acidic Cu site during reaction, which hindered the formation of explosive copper acetylide and ensured the intrinsic safety of Cu/O\u0026minus;FLP catalyst.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we fabricated a Cu/O-FLP catalyst bearing Cu\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ecis\u003c/em\u003e\u0026thinsp;\u0026minus;\u0026thinsp;N\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eCl motif and epoxide group to enhance acetylene hydrochlorination via preferential cleavage of HCl. Theoretical calculation and experimental characterizations revealed that the single atom Cu and epoxide group, acting as Lewis acid-base catalytic sites, synergistically promoted adsorption and dissociation of HCl to form the Cu\u0026thinsp;\u0026minus;\u0026thinsp;Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e and C\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;H\u003csup\u003eδ+\u003c/sup\u003e active species. This not only largely enhanced the acetylene adsorption via both upshift of the d-band center and the microelectric-field-induced polar effect stemming from the electronegativity difference between the formed H\u003csup\u003eδ+\u003c/sup\u003e and Cl\u003csup\u003eδ\u0026ndash;\u003c/sup\u003e species, but also notably reduced the reaction energy barrier of the subsequent rate-limiting step and the desorption energy of vinyl chloride. As a consequence, Cu/O-FLP exhibited an outstanding acetylene conversion efficiency (59.4%), exceeding the corresponding reference catalysts at the same condition. Meanwhile, the preferential HCl activation ensured the saturated six-coordination configuration of single-atom Cu center without forming explosive copper acetylide, thereby endowing Cu-based single-atom catalyst with intrinsic safety.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (22062021), the Science and Technology Project of Xinjiang Bingtuan supported by Central government (2022BC001), the Opening Project of Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan (KF2019010), the Start-Up Foundation for high-level professionals of Shihezi University (RCZK201932) and research project of Shihezi University (CXFZ202205).\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cspan\u003eHutchings, G. and Grady, D. 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N-doped activated carbon from used dyeing wastewater adsorbent as a metal-free catalyst for acetylene hydrochlorination. Chem. Eng. J. \u003cem\u003e371\u003c/em\u003e, 118\u0026ndash;129.\u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-2361952/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2361952/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Simultaneously boosting acetylene hydrochlorination activity and avoiding formation of explosive copper acetylide over Cu-based catalyst, which represented a promising alternative to Hg-based and noble metal catalysts, remained challenging. Herein, we fabricated a frustrated single−atom Cu/O Lewis pair catalyst (Cu/O−FLP) by coupling epoxide group (C−O−C) with atom-dispersed Cu−cis−N2C2Cl center to address this challenge. The basic epoxy site modulated the electron-deficient state of Lewis-acidic Cu center and paired with the Cu−cis−N2C2Cl moiety to preferentially break HCl into different electronegative Cu−Clδ− and C−O−Hδ+ intermediates, which further induced both an extra localized electric field to polarize acetylene and a upshift of the d-band center of catalyst, thereby promoting adsorption and enrichment of acetylene by enhancing the dipolar interaction between acetylene and active intermediates. Moreover, the generated Cu−Clδ− and C−O−Hδ+ drastically reduced the energy barrier of rate-limiting step and made vinyl chloride easier to desorb from the Lewis-basic oxygen-atom site rather than traditional Lewis-acidic Cu center. These superiorities ensured a higher activity of Cu/O-FLP compared with its counterparts. Meanwhile, preferential dissociation of HCl endowed single-atom Cu with the coordination-saturated configuration, which impeded formation of explosive copper acetylide by avoiding the direct interaction between Cu and acetylene, ensuring the intrinsic safety during catalysis.","manuscriptTitle":"Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single−atom Cu/O Lewis pair for acetylene hydrochlorination","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-12-13 16:37:34","doi":"10.21203/rs.3.rs-2361952/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"26dd673c-1c24-4b59-af25-fa1dcd3806ae","owner":[],"postedDate":"December 13th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":17642660,"name":"Physical sciences/Energy science and technology"},{"id":17642661,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2022-12-15T15:38:02+00:00","versionOfRecord":[],"versionCreatedAt":"2022-12-13 16:37:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2361952","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2361952","identity":"rs-2361952","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}