Catalysts For Acetylene Hydrochlorination Research Articles

Convergent Active Site Evolution in Platinum Single Atom Catalysts for Acetylene Hydrochlorination and Implications for Toxicity Minimization.

Platinum single atoms anchored onto activated carbon enable highly stable Hg-free synthesis of vinyl chloride (VCM) via acetylene hydrochlorination. Compared to gold-based alternatives, platinum catalysts are in initial phases of development. Most synthetic approaches rely on chloroplatinic acid, presenting opportunities to explore other precursors and their impact on catalyst structure, reactivity, and toxicity aspects. Here, we synthesize platinum single atom catalysts (Pt SACs, 0.2-0.8 wt % Pt) employing diverse Pt2+ and Pt4+ complexes with ammine, hydroxyl, nitrate, and chloride ligands, following a scalable impregnation protocol on activated carbon extrudates. X-ray absorption spectroscopy (XAS) reveals that Pt4+ species reduce to Pt2+ upon deposition onto the support. Despite similar oxidation states, the initial activity is precursor dependent, with tetraammine-derived Pt SACs displaying 2-fold higher VCM yield than chlorinated counterparts, linked to superior hydrogen chloride binding abilities by density functional theory (DFT) simulations. Their activity gradually converges due to dynamic active site restructuring, delivering remarkable precursor-independent stability over 150 h. Operando XAS and DFT studies uncover reaction-induced ligand exchange, generating common active and stable Pt-Cl x (x = 2-3) species. Convergent active site evolution enables flexibility in metal precursor selection and thus toxicity minimization through multiparameter assessment. This study advances safe-by-design catalysts for VCM synthesis, highlighting the importance of toxicity analyses in early-stage catalyst development programs.

Metal immobilized in a USY zeolite-supported (4-CB)TPPB: A new strategy of enhanced stability for acetylene hydrochlorination

Palladium (Pd)-based catalysts supported by silicaluminate materials are potential as the efficient non-mercury catalyst for acetylene hydrochlorination, which is a necessary industrial reaction for producing vinyl chloride monomer. A new strategy was employed to improve Pd/USY zeolite catalysts taking advantage of 4-carboxybutyl triphenylphosphonium bromide ((4-CB)TPPB) for acetylene hydrochlorination. The most active catalyst (Pd@20(4-CB)TPPB/USY) with the 0.5 wt% Pd loadings and the 20 wt% (4-CB)TPPB additives could achieve a stable acetylene conversion of 99.9 % and the vinyl chloride selectivity of 99.7 % during more than 50 h, outperforming the Pd/USY catalyst. The additive of (4-CB)TPPB was preferential to stabilize the catalytic active Pd species, inhibit the Pd (II) reduction and change the surface acidic properties during the preparation process and reaction, hence restraining the carbon deposition. Density functional theory (DFT) calculations further indicate that (4-CB)TPPB additives could effectively enhance the adsorption energy of catalyst for reactants and the desorption energy of vinyl chloride monomer (VCM) products, thus inhibiting the carbon deposition for improving the catalytic performance of Pd/USY catalysts. These findings provide guidance for designing efficient Pd-based catalysts as well as their utilization for acetylene hydrochlorination.

A Self-Disperse Copper-Based Catalyst Synthesized via a Dry Mixing Method for Acetylene Hydrochlorination

Traditional methods for synthesizing single-site catalysts are typically complicated and require special chemicals due to their tendency to agglomerate. In this study, we present a self-disperse copper-based catalyst synthesized via a dry mixing method for acetylene hydrochlorination. During the reaction, the copper precursor compounds, i.e., CuBr, and CuI, were converted to CuCl. Subsequently, the formed CuCl crystals underwent a significant structural transformation, leading to the formation of small clusters and Cu single sites. The catalytic activity of 5% CuCl + C prepared through the dry mixing method decreased from 93.7% to 92.9% after 100 h of reaction under the condition of GHSV (C2H2) = 60 mL·h−1·g−1. A comparison of the 5% CuCl + C with the 5% CuCl/C obtained by the impregnation method reveals that the catalytic stability of the former was higher than the one prepared by the conventional impregnation method. The exceptional catalytic performance can be attributed to the reaction-induced active sites being highly dispersed and the porous structure of activated carbon being maximally preserved, which was confirmed by HAADF-STEM, BET, TPR, and TG. The reaction-induced dispersion of CuCl on carbon provides a new strategy for preparing single-site catalysts for acetylene hydrochlorination.

The Catalytic Mechanism of [Bmim]Cl-Transition Metal Catalysts for Hydrochlorination of Acetylene

Ionic liquids (ILs) are green solvents involved in chemical reaction and separation processes. In this paper, four ILs-based metal catalysts were prepared by dissolving four transition metal chlorides into 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). Their catalytic performance was measured, and the catalytic mechanism was studied via density functional theory (DFT) based on the analysis of the Mayer bonding order, Mulliken charge, molecular electrostatic potential (ESP), electron localization function (ELF), and partial density of states (PDOS). The results show that the catalytic activity follows the order [Bmim]Cl-RuCl3 > [Bmim]Cl-AgCl > [Bmim]Cl-CuCl2 > [Bmim]Cl-CuCl. [Bmim]Cl helps to dissolve and activate HCl, and the metal chlorides can greatly reduce the activation energy of the reaction. This study provides new insights into the catalytic mechanism of IL, transition metals, and their synergistic effect from a microscopic point of view and sheds light on the development of new catalysts for acetylene hydrochlorination.

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 (COC) 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 COH and CuCl 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.

Progress in mercury-free catalysts for acetylene hydrochlorination

Developing mercury-free catalysts for efficient acetylene hydrochlorination to produce vinyl chloride monomer is crucial for the environment, human health and sustainability.

Ionic liquid–solvent systems in the gas–liquid phase for acetylene hydrochlorination

Ionic liquid–solvent system is an excellent homogeneous catalyst for acetylene hydrochlorination due to its low viscosity, low cost and high activity.

Deep eutectic solvent boosted ruthenium catalysts for acetylene hydrochlorination

Ru-DES/AC catalysts modulate the microchemical environment around the active centre through electron transfer, and the hydrogen bond length between HBD and HBA in DES can be used to design high performance catalysts.

A hierarchically porous carbon stabilized atomically dispersed Au catalyst for acetylene hydrochlorination

The activity of the Au-CSC catalyst is significantly enhanced by the hierarchically porous structure derived from cationic starch, in comparison with that of the microporous Au-SC catalyst obtained from pristine starch.

Data-Informed Discovery of High-Performance Cu-Ligand Catalysts for Acetylene Hydrochlorination

Understanding the relationship between catalyst structure and performance is essential for the rational design of active sites for high-performance Cu-ligand catalysts for acetylene hydrochlorination. Herein, two descriptors are informed by data to screen efficient ligands and predict high-performance Cu-ligand catalysts: (1) the reduction potential of Cu2+-Cu+ and catalytic performance were correlated in a volcano-like manner; (2) the C≡C bond length of C2H2 and catalytic performance were linearly related within the Cu2+-Cu+ reduction limit. By using the two descriptors, the MPPO (3-methyl-1-phenyl-2-phospholene 1-oxide) ligand was successfully identified and developed into an effective Cu-MPPO catalyst. The conversion of C2H2 of 96.11 % and the selectivity of VCM of 99 % were obtained under the conditions of 180 h−1, 180 °C, and VHCl: VC2H2 = 1.2. The C2H2 conversion was still above 90 % after running for more than 600 h at 50 h−1. The excellent activity and exceptional stability of the Cu-MPPO catalyst validate the developed model for optimal ligand selection. Detailed structural characterization and density function theory calculations of the designed catalysts were performed to reveal the relationship between catalyst structure and activity. The results indicated that the addition of MPPO altered the local microenvironment of Cu. The simultaneous increased electron density around Cu and Cl resulted in strengthened HCl adsorption and weakened acetylene adsorption, inhibiting the generation of carbon deposition. In addition, MPPO contributed to suppressing the reduction of Cu species, thus stabilizing the active species. This research provides valuable insights and reference strategies for screening efficient ligands in Cu-ligand catalysts.

Evidence of bifunctionality of carbons and metal atoms in catalyzed acetylene hydrochlorination

Carbon supports are ubiquitous components of heterogeneous catalysts for acetylene hydrochlorination to vinyl chloride, from commercial mercury-based systems to more sustainable metal single-atom alternatives. Their potential co-catalytic role has long been postulated but never unequivocally demonstrated. Herein, we evidence the bifunctionality of carbons and metal sites in the acetylene hydrochlorination catalytic cycle. Combining operando X-ray absorption spectroscopy with other spectroscopic and kinetic analyses, we monitor the structure of single metal atoms (Pt, Au, Ru) and carbon supports (activated, non-activated, and nitrogen-doped) from catalyst synthesis, using various procedures, to operation at different conditions. Metal atoms exclusively activate hydrogen chloride, while metal-neighboring sites in the support bind acetylene. Resolving the coordination environment of working metal atoms guides theoretical simulations in proposing potential binding sites for acetylene in the support and a viable reaction profile. Expanding from single-atom to ensemble catalysis, these results reinforce the importance of optimizing both metal and support components to leverage the distinct functions of each for advancing catalyst design.

Effect of R-SO2-R′ ligands on the gold-based catalysts for acetylene hydrochlorination: A DFT study

Gold-based mercury-free catalysts have great potential in the industrial production of vinyl chloride. In order to further understand the factors affecting the catalytic activity, the catalytic reaction mechanisms of five kinds of sulfur-containing ligand gold-based catalysts are studied by DFT calculation at the PBE0/def2-TZVP level, and dispersion-corrected DFT-D3 is performed. The results show that the rate control step in the reaction path is the transfer of proton hydrogen. With the increase of Mulliken charges of Au and S atoms in the catalyst, the energy barrier of acetylene hydrochlorination decreases. The catalyst formed by methanesulfonic acid and AuCl3 has the lowest energy barrier of acetylene hydrochlorination (23.18 kcal/mol). Compared to AuCl3 catalyst, adding ligands can significantly reduce the products desorption energy. When the ligand has an electron-withdrawing group, the corresponding acetylene self-polymerization barrier is lower. These results provide valuable theoretical guidance for preparation of efficient sulfur-containing ligand gold-based catalysts in future.

Excess Copper Chloride Induces Active Sites over Cu-Ligand Catalysts for Acetylene Hydrochlorination

Active sites on ligand-enhanced Cu-based catalysts for acetylene hydrochlorination have not been clearly identified yet due to their complex nature and dynamic evolution under working conditions. Herein, we correlate experimental measurements with theoretical simulations to show that the indirect ligand-coordinated sites induced by excess copper chloride are superior. The catalyst experimentally exhibits a unique dual nature that the catalytic activity could be inhibited or boosted by changing the ratio of copper chloride and ligand. By adopting molecular dynamics simulation to obtain the dynamic evolution of active sites, coupled with density functional theory calculations, we show that excess copper chloride molecules spontaneously assemble into chain structures, thus inducing indirect ligand-coordinated sites which together with the electron transfer along the copper chloride chain are crucial for the high catalytic activity. This knowledge provides fundamental insights into the origin of activity in Cu-ligand catalysts for acetylene hydrochlorination and the identification of active sites in complex catalytic systems.

Study on quantitative structure of coke deposition in UDH catalyst for acetylene hydrochlorination

ABSTRACT The catalyst made of Au, Cu and K according to a certain ratio which is defined as a UDH catalyst has a great catalytic effect on acetylene hydrochlorination. In order to clarify the formation mechanism of coke deposition in catalyst, the structure of coke deposition was quantified. Carbon deposits in the UDH catalyst are separated using Soxhlet extraction and rotary evaporation. Experimental techniques like gel chromatography, elemental analysis, H-NMR and FT-IR were applied for the characterization of coke deposition. The quantitative structure of the coke deposition was evaluated by the improved B-L method. The results show that the average molecular formula of the coke deposition is C40.82H33Cl15.55 which is a complex multiple-ring structure containing seven aromatic rings and five six-membered cycloalkane rings. The aromatic carbon fraction of the calculated coke deposition is 0.623, and the ratio of hydrogen to carbon atomic which are not replaced in aromatic ring moieties is 0.313. These results indicate that in the side reaction of acetylene hydrochlorination, substances with the ring structure are more likely to be generated, and the ring structure continues to increase, eventually forming coke deposition.

Research progress on modification of mercury-free metal catalysts for acetylene hydrochlorination

Research progress on modification of mercury-free metal catalysts for acetylene hydrochlorination

Enhanced performance of Pd-[DBU][Cl]/AC mercury-free catalysts in acetylene hydrochlorination

Compared with the rapid deactivation of the Pd/AC catalyst, an eco-friendly Pd-[DBU][Cl]/AC ([DBU][Cl], 1,8-diazabicyclo[5.4.0]undec-7-ene hydrochloride) catalyst with enhanced stability was synthesized and applied in the hydrochlorination of acetylene. The Pd-20[DBU][Cl]/AC catalyst exhibits 96.7% acetylene conversion and 98.9% selectivity of vinyl chloride within the 24 h evaluation under the conditions of T = 180 °C, GHSV(C2H2) = 360 h–1 and V(HCl)/V(C2H2) = 1.2. The enhanced stability of the Pd-[DBU][Cl]/AC catalyst is attributed to the prevention of the reduction of Pd(II) to Pd(0), the inhibition of the formation of coke deposition on the catalyst surface, and the reduction of the loss of Pd species during the reaction. TPD characterization and DFT theoretical simulations confirmed that the PdCl2-[DBU][Cl] complex has stronger adsorption of HCl and weaker adsorption of C2H2 and C2H3Cl compared to PdCl2. Furthermore, the catalytic mechanism of acetylene hydrochlorination over the PdCl2 and PdCl2-[DBU][Cl] site was put forward based on theoretical simulations. The good activity and stability of Pd-20[DBU][Cl]/AC in the 60 h lifetime test indicates that it is likely to be a promising alternative to HgCl2 catalysts.

Construction of Highly Dispersed Cu–P/Cl Active Sites Using Methyldiphenyloxophosphine for Efficient Acetylene Hydrochlorination

To overcome the disadvantages of Cu-based catalysts, such as the low dispersion of active components and insufficient active species, several 15% Cu-Lx/AC catalysts for acetylene hydrochlorination were synthesized based on strong interactions between a ligand and CuCl2 precursors. The introduction of the methyldiphenyloxophosphine (MDPO) ligand effectively modulated the electronic properties of the metal centers, which contributed to the construction of a highly dispersed Cu–P/Cl local structure with Cu1+/Cu2+ as a plausible active center. The sintering of active components in the catalyst may be one of the main reasons for the decrease in catalytic performance. Meanwhile, the enhanced adsorption and activation of the catalyst for C2H2 and HCl molecules resulted in improved coking resistance. The most active catalyst (15% Cu8MDPO1/AC) could achieve a stable acetylene conversion of 97% at 180 °C, a gas hourly space velocity (GHSV) (C2H2) of 180 h–1, and a feed volume ratio (VHCl/VC2H2) of 1.15, outperforming the benchmark catalyst. The excellent activity and stability in a 300 h laboratory test at a high GHSV and a 3414 h industrial sideline test at an industrial GHSV render the 15% Cu8MDPO1/AC catalyst as a reference for the construction of other catalysts from an environmental, economic, and application prospect perspective.

Deactivation and Regeneration of Nitrogen Doped Carbon Catalyst for Acetylene Hydrochlorination.

The poor stability of carbon materials doped with nitrogen limited their development in acetylene hydrochlorination. Therefore, investigating the deactivation reasons of carbon catalysts and researching regeneration methods became the research focus. Herein, carbon-nitrogen materials were synthesized by one-step pyrolysis, which using biomass materials with high nitrogen content, the synthesized material was used in an acetylene hydrochlorination reaction. The acetylene conversion rate of D-GH-800 catalyst was up to 99%, but the catalytic activity decreased by 30% after 60 h reaction. Thermogravimetric analysis results showed that the coke content was 5.87%, resulting in catalyst deactivation. Temperature-programmed desorption verified that the deactivation was due to the strong adsorption and difficult desorption of acetylene by the D-GH-800 catalyst, resulting in the accumulation of acetylene on the catalyst surface to form carbon polymers and leading to the pore blockage phenomenon. Furthermore, based on the catalyst deactivation by carbon accumulation, we proposed a new idea of regeneration by ZnCl2 activation to eliminate carbon deposition in the pores of the deactivated catalyst. As a result, the activity of D-GH-800 was recovered, and lifetime was also extended. Our strategy illustrated the mechanism of carbon deposition, and the recoverability of the catalyst has promising applications.

Efficient and stable N-heterocyclic ketone-Cu complex catalysts for acetylene hydrochlorination: the promotion effect of ligands revealed from DFT calculations.

Cu-based catalysts are a promising alternative to toxic mercury catalysts for acetylene hydrochlorination, but their effectiveness is limited due to the poor dispersion and deactivation caused by reduction, agglomeration, and carbon deposition. In this study, the activity and stability of carbon-supported CuCl2 catalysts were largely improved by introducing N-heterocyclic ketones. Remarkably, N-methyl-2-pyridone (NM2P) coordinated Cu-based catalysts exhibited over 95% acetylene conversion with better stability under the reaction conditions of T = 180 °C, GHSV (C2H2) of 80 h-1, and VHCl/VC2H2 = 1.2. The combined results of characterization and exhaustive density functional theory (DFT) calculations revealed that the O-Cu coordination between the NM2P ligand and Cu cation strengthened the combination of reactants and Cu active sites, lowering the key reaction energy barrier, thereby leading to high activity. Meanwhile, the addition of the NM2P ligand significantly inhibited the reduction of Cu2+ to Cu+/Cu0, avoiding the formation of CuCl aggregates and the coking caused by Cu0, enhancing the catalytic stability. Overall, our study provides important insights into the design and optimization of Cu-based catalysts for acetylene hydrochlorination.

Halloysite nanotube-supported bismuth catalysts for acetylene hydrochlorination

A novel supported bismuth (Bi)-based catalyst was prepared using halloysite nanotubes (HNTs) as a carrier and effectively used for acetylene hydrochlorination.