Evaluation and application of kinetic models for Cu-catalyzed acetylene hydrochlorination

The development of environmentally friendly catalysts has become a top priority for acetylene hydrochlorination.However,difficulties remain in systematic studies on the applicability of kinetic models for the industrialization of Cu-based catalysts.Therefore,a strategy involving reactor modeling,parameter estimation,and model testing is developed to evaluate the predictive ability of kinetic models.In order to search for reliable and widely applicable reaction kinetic models for Cu-based catalysts,a case study is conducted.Multiple possible kinetic models derived from the power law,adsorption mechanism,and reaction path are sifted through collecting and testing activity data from tens of Cu-based catalysts.Different optimum applicable ranges of these kinetic models are presented.According to the comparative analysis on their applications in various industrial scenarios,this research suggests that kinetic models derived from reaction path exhibits the best extrapolation ability and has the greatest potential for application in the scale-up design of reactors.

Electron-deficient Cu site catalyzed acetylene hydrochlorination

Rational design of catalytic sites to activate the C≡C bond is of paramount importance to advance acetylene hydrochlorination. Herein, Cu sites with electron-rich and electron-deficient states were constructed by controlling the impregnation solutions. The π electrons flowing from acetylene to Cu site are facilitated over the electron-deficient Cu sites, achieving high activation of C≡C bond. The contradiction between the increased activation of acetylene required for enhanced catalytic activity and the resistance of Cu site to reduction by acetylene required for maintaining catalytic stability can be balanced by establishing strong interactions of Cu site with pyrrolic-N species. The catalytic activity displays a volcano shape scaling relationship as a function of Cu particle size. Tribasic copper chloride is concomitantly generated with the construction of electron-deficient Cu sites. The H–Cl bond of HCl can be activated over the tribasic copper chloride, accelerating the surface reaction of vinyl chloride production. This strategy of inducing electron deficiency provides new insight into the rational design of catalysts for the synthesis of vinyl chloride with a high catalytic performance.

Nitrogen and phosphorus co-doped activated carbon induces high density Cu^(+)active center for acetylene hydrochlorination

This work aims to solve the problems of low reaction activity of Cu-based catalysts and agglomeration of active centers in acetylene hydrochlorination.Cu-based catalysts supported by NAP co-doped activated carbon(AC)with different content(mCu-xNP/AC)were manufactured and applied in the acetylene hydrochlorination reaction.It was found that the doping of carriers N and P induced the transformation of Cu^(2+)to Cu^(+),and the catalytic activity was markedly improved.Under the optimal reaction temperature of 220℃,the gas hourly space velocity(GHSV)of C_(2)H_(2)was 90 h^(-1)and V_(HCl):V_(C_(2)H_(2))was 1.15.The initial activity of the 5%Cu-30 NP/AC catalyst reached 95.59%.Through some characterization methods showed the addition of N and P improved the dispersion of Cu in carbon,which increased the ratio of Cu^+/Cu^(2+).The measurement results confirmed that the chemisorption capacity of mCu-xNP/AC for C_(2)H_(2)decreased slightly,and the chemisorption capacity for HCl increased significantly,which was the reason for the increased activity of the catalyst.The conclusion provides a reference for the development of acetylene hydrochlorination Cu catalyst.

Regulating the coordination environment of Ru single-atom catalysts and unravelling the reaction path of acetylene hydrochlorination

In this work,DFT calculations were used firstly to simulate the nitrogen coordinated metal single-atom catalysts(M-N_(x)SACs,M=Hg,Cu,Au,and Ru) to predict their catalytic activities in acetylene hydrochlorination.The DFT results showed that Ru-N_(x)SACs had the best catalytic performance among the four catalysts,and Ru-N_(x)SACs could effectively inhibit the reduction of ruthenium cation.To verify the DFT results,Ru-N_(x)SACs were fabricated by pyrolyzing MOFs in-situ spatially confined metal precursors.The N coordination environment could be controlled by changing the pyrolysis temperature.Catalytic performance tests indicated that low N coordination number(Ru-N_(2),Ru-N_(3))exhibited excellent catalytic activity and stability compared to RuCl_(3)catalyst.DFT calculations further revealed that Ru-N_(2)and Ru-N_(3)had a tendency to activate HCl at the first step of reaction,whereas Ru-N4tended to activate C_(2)H_(2).These findings will serve as a reference for the design and control of metal active sites.

Acetylene hydrochlorination over supported ionic liquid phase(SILP)gold-based catalyst:Stabilization of cationic Au species via chemical activation of hydrogen chloride and corresponding mechanisms

The activation of HCl by cationic Au in the presence of C2H2 is important for the construction of active Au sites and in acetylene hydrochlorination.Here,we report a strategy for activating HCl by the Au-based supported ionic liquid phase(Au–SILP)technology with the[N(CN)2^–]anion.This strategy enables HCl to accept electrons from[N(CN)2^–]anions in Au–[N(CN)2^–]complexes rather than from pure[Bmim][N(CN)2],leading to notable improvement in both the reaction path and the stability of the catalyst without changing the reaction triggered by acetylene adsorption.Furthermore,the induction period of the Au–SILP catalyst was shown to be absent in the reaction process due to the high Au(III)content in the Au(Ⅲ)/Au(Ⅰ)site and the high substrate diffusion rate in the ionic liquid layer.This work provides a facile method to improve the stability of Au-based catalysts for acetylene hydrochlorination.

Efficient and stable Ru(Ⅲ)-choline chloride catalyst system with low Ru content for non-mercury acetylene hydrochlorination

Herein,we report an excellent,supported Ru(III)‐ChCl/AC catalyst with lower Ru content,where the ionic complex ChRuCl4 serves as the active component for acetylene hydrochlorination.The prepared heterogeneous Ru‐10%ChCl/AC catalyst shows excellent activity and long‐term stability.In this system,ChCl provides an environment for the ChRuCl4 to be stabilized as Ru(III),thus suppressing the reduction of the active species and the aggregation of ruthenium species during the reaction.The interaction between reactants and catalyst species was investigated by catalyst characterizations in combination with DFT calculations to disclose the effect of the ChRuCl4 complex and ChCl on the catalytic performance.This inexpensive,efficient,and long‐term catalyst is a competitive candidate for application in the hydrochlorination industry.

Carbon-supported ruthenium catalysts prepared by a coordination strategy for acetylene hydrochlorination

The development of efficient and stable non-mercury catalysts for the chlor-alkali industry is desirable but remains a great challenge.Herein,we design a series of ruthenium catalysts for acetylene hydrochlorination by regulating the electronic structure of ruthenium ions through coordination with various ligands(thiourea,phenanthroline,and L-lactic).The turnover frequencies(TOFs)and apparent activation energies for the acetylene hydrochlorination have a linear relationship with the binding energy of Ru3+in the ruthenium catalysts.The synergetic effect of the ruthenium ion and ligands plays an important role in acetylene hydrochlorination.The Ru-Thi/AC catalyst with thiourea as the ligand shows the highest TOF and stability in acetylene hydrochlorination.The present study provides a rational method to regulate the electronic structure of supported metal catalysts with high catalytic performance exhibited by the carbon-supported heterogeneous catalysts.

Wheat flour-derived N-doped mesoporous carbon extrudes as an efficient support for Au catalyst in acetylene hydrochlorination

We recently reported an N‐doped mesoporous carbon(N‐MC)extrudate,with major quaternary N species,prepared by a cheap and convenient method through direct carbonization of wheat flour with silica,which has excellent catalytic performance in acetylene hydrochlorination.Herein,we examined the activity of Au supported on N‐MC(Au/N‐MC)and compared it with that of Au supported on nitrogen‐free mesoporous carbon(Au/MC).The acetylene conversion of Au/N‐MC was 50%at 180°C with an acetylene space velocity of 600 h–1 and VHCl/VC2H2 of 1.1,which was double the activity of Au/MC(25%).The introduced nitrogen atoms acted as anchor sites that stabilized the Au3+species and inhibited the reduction of Au3+to Au0 during the preparation of Au/N‐MC catalysts.

High nitrogen carbon material with rich defects as a highly efficient metal-free catalyst for excellent catalytic performance of acetylene hydrochlorination

In this work,we developed a simple strategy to synthesize a carbon material with high nitrogen and rich carbon defects.Our approach polymerized diaminopyridine(DAP) and ammonium persulfate(APS).Following a range of different temperature pyrolysis approaches,the resulting rough surface was shown to exhibit edge defects due to N-doping on graphite carbon.A series of catalysts were evaluated using a variety of characterization techniques and tested for catalytic performance.The catalytic performance of the N-doped carbon material enhanced alongside an increment in carbon defects.The NC-800 catalyst exhibited outstanding catalytic activity and stability in acetylene hydrochlorination(C_(2) H_(2) GHSV=30 h^(-1),at 220℃,the acetylene conversion rate was 98%),with its stability reaching up to 450 h.Due to NC-800 having a nitrogen content of up to 13.46%,it had the largest specific surface area and a high defect amount,as well as strong C_(2) H_(2) and HCl adsorption.NC-800 has excellent catalytic activity and stability to reflect its unlimited potential as a carbon material.

Melamine Modification of Spherical Activated Carbon and Its Effects on Acetylene Hydrochlorination

Commercial spherical activated carbon（SAC） was modified by impregnation to enhance the catalytic properties of SAC in acetylene hydrochlorination through melamine modification. Different modification conditions for SAC with nitrogen were compared by changing the SAC-Melamine ratios. The effect of carbonization temperature on the modification was also investigated. Surface chemistry and adsorption properties of the modified and unmodified SACs were studied by scanning electron microscope（SEM）, X-ray photoelectron spectroscopy（XPS）, elementary analysis, BET, and temperature-programmed desorption（TPD）. Moreover, the catalytic properties of SAC in acetylene hydrochlorination under differently modified conditions were also investigated. Elemental analysis showed that the nitrogen content of the modified SAC was greatly improved. XPS revealed that nitrogen mainly exists in Pyrrole nitrogen and Pyridine nitrogen. TPD showed that desorption of C2H2 was changed by modification. The conversion rate of acetylene was up to 70% under the following reaction conditions： temperature, 150 ℃; C2H2 hourly space velocity（GHSV）, 36 h-1; feed volume ratio V（HCl）/V（C2H2） = 1.15. The catalytic properties of SAC were improved significantly via melamine modification.

Surface chemical characterization of deactivated low-level mercury catalysts for acetylene hydrochlorination

Mercury-containing catalysts are widely used for acetylene hydrochlorination in China. Surface chemical characteristics of the fresh low-level mercury catalysts and spent low-level mercury catalysts were compared using multiple characterization methods. Pore blockage and active site coverage caused by chlorine-containing organics are responsible for catalyst deactivation. The reactions of chloroethylene and acetylene with chlorine free radical can generate chlorine-containing organic species. SiO_2 and functional groups on activated carbon contribute to the generation of carbon deposition. No significant reduction in the total content of mercury was observed after catalyst deactivation, while there was mercury loss locally. The irreversible loss of HgCl_2 caused by volatilization, reduction and poisoning of elements S and P also can lead to catalyst deactivation. Si, Al, Ca and Fe oxides are scattered on the activated carbon. Active components are still uniformly absorbed on activated carbon after catalyst deactivation.

Process monitoring of the Au-S bond conversion in acetylene hydrochlorination

The continuous expansion of vinyl chloride production increases environmental pollution caused by mercury catalysts,which is an issue that urgently needs to be solved.Green and stable catalysts should be researched to alleviate this issue.In this research,Thiolactic acid acts as a ligand where sulfhydryl groups form a stable complex with Au on the surface of a spherical activated carbon(SAC).An Au-thiolactic acid/SAC catalyst was designed with a Au theoretical loading of 0.5%(mass)to overcome the disadvantages of traditional Au-based catalysts,such as a low conversion rate and poor life cycle.The ratio of Au to ligand was screened,and the activity was best when Au/S=1:8.The formation of the Au-S bond was proven by FT-IR and UV-vis.The longevity test of the Au1 S8/SAC catalyst was carried out at 1200 h^(-1) for 50 h.Samples with reaction times of 0 h,5 h,10 h,20 h,and 50 h were taken to monitor the catalyst status.The XPS and TPR tests proved that the Au-S bond broke as the acetylene hydrochlorination reaction proceeded,The DFT calculation proved that the Au-S bond is the active site,and the sulfur atom promotes the adsorption of C_(2)H_(2) by the catalyst.

Stabilizing supported gold catalysts in acetylene hydrochlorination by constructing an acetylene–deficient reaction phase

In the process of acetylene hydrochlorination,the rapid deactivation of supported gold(Au)catalysts by acetylene is still a huge challenge.Here,we provide an innovative strategy for constructing an acetylene–deficient reaction phase on the active site by coating an ionic liquid film on the Au(H2O)/C surface.The reactant ratio of C2H2 to HCl in this acetylene–deficient reaction phase is 1:132,in contrast to the 1:1 M ratio in the gas phase,thus boosting the catalytic stability of Au(H2O)/C catalysts.The kinetic and theoretical analysis showed that the reduction of cationic gold by C2H2 and the generation of carbon deposition can be inhibited in this constructed reaction phase during reaction.The current work not only broadens the scope of supported Au catalysts in acetylene hydrochlorination,but also verifies the perspective of the tunability of stoichiometric balance,which can be used in other catalytic applications.

Promotion effect of epoxy group neighboring single-atom Cu site on acetylene hydrochlorination

Carbon materials have been used as the support for catalysts in the field of acetylene hydrochlorination,the influence of inevitable oxygen-containing moieties on the reaction is often ignored and the mechanism of the oxygen-doping structure remains ambiguous.Herein,we explored the effect of the oxygen-containing group(C-O-C)in the support on the activity of single-atom dispersed Cu catalysts.By immersing the Cu single-atom catalyst in an alkaline solution,the epoxy species on the carbon support was cleaved to obtain a pure ether species while the Cu site was modified to a more electron-deficient state.The turnover frequency value of Cu/O-FLP catalyst with epoxy groups was 1.6-fold higher than that of alkaline treated catalyst.Our result indicated that the epoxy groups could assist adjacent single-atom Cu sites to synergistically promote the adsorption and cleavage of the reactant hydrogen chloride toward form C-OH and Cu-Cl bonds,and reduce the reaction energy barrier.The presence of electron deficient Cu sites and ether species could induce competitive adsorption of the acetylene and hydrogen chloride,thereby reducing the activity of the catalyst.This study highlights the influence of surface oxygen species and the tunability of the support,providing the foundation for the fabrication of higher-activity Cu catalysts 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

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 atomdispersed Cu-cis-N_(2)C_(2)Cl center to address this challenge.The basic epoxy site modulated the electron-deficient state of Lewisacidic Cu center and paired with the Cu-cis-N_(2)C_(2)Cl moiety to preferentially break HCl into different electronegative Cu-Clδ-and C-O-H^(δ+)intermediates,which further induced both an extra localized electric field to polarize acetylene and a upshift of the dband 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-H^(δ+)drastically reduced the energy barrier of ratelimiting 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.

Free radicals induced ultra-rapid synthesis of N-doped carbon sphere catalyst with boosted pyrrolic N active sites for efficient acetylene hydrochlorination

Activated carbon-supported HgCl2 catalysts have seriously impeded the development of the polyvinyl chloride(PVC)industry due to the sublimation of Hg species and environmental pollution problems.Herein,the template-free and organic solvent-free strategy was devised to synthesize non-metallic based nitrogen-doped carbon(U-NC)sphere catalyst for acetylene hydrochlorination.This green strategy via ultrasonic chemistry initiates resin crosslinking reactions between aminophenol and formaldehyde resin by free radicals,leading to the ultra-rapid formation of U-NC with remarkably high pyrrolic N content in only 5 min.This U-NC catalyst exhibited an outstanding space-time-yield(1.6 gVCM·gcat^(−1)·h^(−1)),even comparable to the reported metallic catalyst.By combining kinetic analysis,advanced characterizations,density functional theory,it is found that the amount of pyrrolic N is in linear with C_(2)H_(2)conversion,pyrrolic N in U-NC can effectively improve acetylene hydrochlorination performance by mediating HCl adsorption.This work sheds new light on rationally constructing metal-free catalyst for acetylene hydrochlorination.

Application of SnO_(x)/AC catalyst for the acetylene hydrochlorination

In this work,SnO_(x)/activated carbon(AC)was synthesized by hydrothermal method,which was applied to acetylene hydrochlorination.Characterizations showed the SnO_(x)nanoparticles were uniformly dispersed on the carbon,with the coexistence of SnO and SnO_(2).The acetylene conversion of SnO_(x)/AC was 75%,much higher than that of SnCl_(4)/AC.It was shown that the adsorption of reactants on SnO_(x)was stronger than on SnCl_(4).Theoretical calculations showed the adsorption energies of reactants on SnO_(x)were thermodynamically favorable and suggested that Sn^(4+)and Sn^(2+)in SnO_(x)have different adsorption capacities for reactants.Through adjusting the valence ratio of SnO_(x),SnO_(x)/AC O 4 h(O for oxidation)exhibited the best catalytic performance and had the strongest adsorption capacity for the reactants.However,the SnO_(x)/AC catalyst was easily deactivated during acetylene hydrochlorination due to the loss of Sn.The doping of N effectively reduced the loss of Sn and improved the stability of the catalyst due to the anchoring effect of N on the SnO_(x)particles.

Active carbon supported S-promoted Bi catalysts for acetylene hydrochlorination reaction

In the present work, the sulfur doped bismuth-based catalysts were prepared by incipient wetness impregnation method and used for the hydrochlorination of acetylene to vinyl chloride monomer （VCM） in a fixed-bed reactor. The effect of introduction of S was characterized by N2 adsorption-desorption, powder X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction and X-ray photoelectron spectroscopy. The characterization results indicated that the doping of S resulted in the increase of Brunauer-Emmett-Teller （BET） surface areas and decrease of active species particle size for the Bi-based catalysts, which led to more accessible active sites, and consequently boosted the catalytic hydrochlorination activity. The effect of H2SO4 concentration on the activity of this type catalyst was examined, and the results showed that there is an optimal loading of H2SO4 （S/Bi=0.5 mol/mol）, at which the conversion of C2H2 was enhanced to 81% under the reaction condition and coke deposition is a main reason for the deactivation of catalyst.

The activity and stability of PdCl_2/C-N catalyst for acetylene hydrochlorination

Carbon supported PdCl_2 is highly active in catalyzing acetylene hydrochlorination reaction, but deactivates rather quickly. Upon nitrogen doping in the carbon structure, the stability of the PdCl_2 catalysts is significantly improved. Furthermore, the results show that 900 ℃ is a preferred doping temperature. The acetylene conversion keeps above 90% even after 1200 min time on stream whereas the one without nitrogen doping drops to below 10% after 450 min. The stabilizing mechanism of nitrogen doping on catalyst was studied.

One-pot synthesis of nitrogen and sulfur co-doped activated carbon supported AuCl_3 as efficient catalysts for acetylene hydrochlorination

Commercialization of acetylene hydrochlorination using AuCl3 catalysts has been impeded by its poor stability. We have been studying that nitrogen-modified Au/NAC catalyst delivered a stable performance which can improve acetylene hydrochlorination activity and has resistance to catalytic deactivation. Here we show that nitrogen and sulfur co-doped activated carbon supported AuCl3 catalyst worked as efficient catalysts for the hydrochlorination of acetylene to vinyl chloride. Au/NSAC catalyst demonstrated high activity comparative to Au/AC catalyst. Furthermore, it also delivered stable performance within the selectivity of acetylene, reaching more than 99.5%, and there was only a 3.3% C2H2 conversion loss after running for 12 h under the reaction conditions of a temperature of 180 C and a C2H2 hourly space velocity of 1480 h 1. The presence of the sulfur atoms may serve to immobilize/ anchor the Au and also help prevent reduction and sintering of the Au and hence improve the catalytic activity and stability. The excellent catalytic performance of the Au/NSAC catalyst demonstrated its potential as an alternative to mercury chloride catalysts for acetylene hydrochlorination.