The catalytic performance of metal-free defected carbon catalyst towards acetylene hydrochlorination revealed from first-principles calculation

Defected carbon materials as a metal-free catalyst have shown superior stability and catalytic performance in the acetylene hydrochlorination reaction. Through density functional theory (DFT) calculations, for the first time, several different defected configurations comprising mono and divacancies and Stone Wales defect on single-walled carbon nanotubes (SWCNTs) have been used as a direct catalyst for acetylene hydrochlorination reaction. These defective sites on SWCNTs are the most active site for acetylene hydrochlorination reaction compare to pristine SWCNT. The different configurations of defects have different electronic structures, which specify that monovacancy defects have more states adjacent to the Fermi level. The reactant acetylene (C₂H₂) adsorbed strongly compared to hydrogen chloride (HCl) and expected to be the initial step of the reaction. Acetylene adsorbed strongly at monovacancy defected SWCNT compared to other investigated defects. Reaction pathway analysis revealed that mono- and divacancy defected SWCNTs have minimum energy barriers and show extraordinary performance toward acetylene hydrochlorination. This work suggests the potential of metal-free defected carbon in catalyzing acetylene hydrochlorination and provides a solid base for future developments in acetylene hydrochlorination.     

In situ K-edge X-ray absorption spectroscopy of the ligand environment of single-site Au/C catalysts during acetylene hydrochlorination

The replacement of HgCl₂/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl⁻, Au–Cl, and C–Cl and how these species evolve during reaction. Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C₂H₂ alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst.

In situ chlorine and sulphur XAS shows a dynamic ligand environment around cationic Au single-sites during 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.     

The activity and stability of PdCl<Subscript>2</Subscript>/C-N catalyst for acetylene hydrochlorination

Carbon supported PdCl₂ is highly active in catalyzing acetylene hydrochlorination reaction, but deactivates rather quickly. Upon nitrogen doping in the carbon structure, the stability of the PdCl₂ catalysts is significantly improved. Furthermore, the results show that 900 °C 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.     

Pyrrolidone ligand improved Cu‐based catalysts with high performance for acetylene hydrochlorination

A series of Cu‐pyrrolidone/spherical activated carbon (SAC) catalysts were prepared via a simple incipient wetness impregnation method and then assessed in acetylene hydrochlorination, and the catalytic evaluation result indicated that the 1‐methyl‐2‐pyrrolidinone (NMP) ligand was found to be the most effective one to significantly improve the activity and stability of Cu catalyst. The catalyst with the optimal molar ratio of NMP/Cu = 0.25 showed 94.2% acetylene conversion at 180°C and an acetylene gas hourly space velocity of 180 h^?1. Moreover, the acetylene conversion of Cu‐0.25NMP/SAC remained stable over 99.1% for about 220 h under the industrial condition. Transmission electron microscopy (TEM) analyses proved that NMP ligand improved the dispersion of Cu species. In addition, hydrogen temperature‐programmed reduction (H₂‐TPR), X‐ray photoelectron spectra (XPS), thermogravimetric analysis (TGA), and Brunner–Emmet–Teller (BET) indicated that the additive of NMP was preferential to stabilize the catalytic active Cu⁺ and Cu²⁺ species and inhibit the reduction of Cu^α+ to Cu⁰ during the preparation process and reaction, hence restraining the coke deposition. Furthermore, the steady coordination structure between Cu and NMP was confirmed by Fourier‐transform infrared spectra (FT‐IR) and Raman combining with density functional theory (DFT) calculation, which could effectively lower the adsorption energy of catalyst for C₂H₂ and inhibit the serious carbon deposition caused by excessive acetylene self‐accumulation. Our findings suggest that the efficient, well‐stabilized cost‐effective, and environmentally friendly Cu catalyst has great potential in acetylene hydrochlorination.     

Evaluation and applications of a gaseous mercuric chloride source

In this study, a diffusion-type device for generating gaseous mercuric chloride (HgCl₂) was systematically evaluated and applied to validate the annular denuder method for sampling gaseous HgCl₂ species in a synthetic gas stream. The results show that it takes at least 48 h for the system to reach a steady-state condition after the diffusion cell reaches the temperature set-point and the carrier gas is activated. The primary Hg species from the source was proven to be HgCl₂. In the temperature range from –5.00 to 11.80 °C, the Hg emission rates from the source vary from 1.8 to 14.2 pg min^–1. It is shown that, under the experimental conditions examined, KCl-coated annular quartz denuders designed for ambient reactive gaseous mercury (RGM) collection could quantitatively collect HgCl₂. It is also demonstrated that the impactors used to remove coarse airborne particulate matter could lead to a loss of up to one third of the HgCl₂ in the gas stream.     

Wide Band Gap Organic–Inorganic Hybrid (CH3NH3)2HgCl4 as Self-Driven Ultraviolet Photodetector and Photoconductor

At present, developing new organic–inorganic hybrid materials (OIHM) and studying their photoelectric properties is an important research field. In this work, the OIHM (CH₃NH₃)₂HgCl₄ (MA₂HgCl₄) single crystal and thin film are prepared. The results show that the crystal structure of MA₂HgCl₄ has a monoclinic crystal system with P2₁/c (14) space group (unit cell dimensions 7.776 × 12.917 × 10.993 Å, 90.00 × 96.366 × 90.00) by solving the single crystal diffraction data. The band gap of MA₂HgCl₄ is calculated to be approximately 3.21 eV. To the best of our knowledge, this is the first study on MA₂HgCl₄ for optoelectronic application. The photodetector based on MA₂HgCl₄ thin film is highly selective for ultraviolet (UV) light (369 nm), and has a poor response for visible light. The electrochemical impedance spectrum shows that the impedance value (2 kΩ) of the device under 369 nm UV light is four magnitudes lower than that (10⁷ Ω) under dark. Thus, MA₂HgCl₄ has the nature of a photoconductor. The density functional theory indicates that the valence band maximum (VBM) of MA₂HgCl₄ is mainly derived from Cl-3p state, Hg-5d state and organic CH₃NH₃⁺ state also participate in the formation of the VBM band. The electron states of VBM and the conduction band minimum of MA₂HgCl₄ come from inorganic HgCl₄²⁻ clusters.     

Improvement of the stability of Hg/AC catalysts by CsCl for the high-temperature hydrochlorination of acetylene

Activated carbon-supported mercuric chloride(HgCl_2) is used as an industrial catalyst for acetylene hydrochlorination. However, the characteristic of easy sublimation of HgCl_2 leads to the deactivation o the catalyst. Here, we showed that the thermal stability of the Hg/AC catalyst can be evidently improved when Cs Cl is added into the Hg/AC catalyst. Compared with the pure Hg/AC catalyst, the sublimation rate of HgCl_2 from the Hg–Cs/AC catalyst decreased significantly and the Hg–Cs/AC catalyst showed bette catalytic activity and stability in the reaction. This promoting effect is related to the existence of cesium mercuric chlorides(Cs_xHg_yCl_(x+2y)) highlighted by XRD, HR-TEM and EDX analyses. Thus, reacting HgCl_2 with alkali chlorides to form alkali-mercuric chlorides may be a key to design highly efficient and thermally stable mercuric chloride catalyst for hydrochlorination reactions.     

Effect of mechanicochemical treatment on the activity of K<Subscript>2</Subscript>PdCl<Subscript>4</Subscript> in the heterogeneous catalytic hydrochlorination of acetylene

A heterogeneous catalyst for the hydrochlorination of acetylene using gaseous HCl was obtained by prior mechanical activation of K₂PdCl₄ powder in an atmosphere of acetylene or propylene. Active sites are formed during the mechanical treatment in the surface layers of the catalyst, which are Pd(II) complexes with a coordination vacancy.     

Kinetics modeling of the volatilization of mercury compounds involved in spent mercury-containing catalyst under microwave irradiation

The industrial design and development of microwave-induced volatilization of hazardous substances in waste greatly depend on their dielectric properties. The dielectric properties of different mercury compounds in spent mercury-containing catalyst (SAC) were investigated by the cavity perturbation method at different temperatures. The decomposition absorption mechanisms for HgS and HgCl₂ show the same trend according to thermogravimetric analysis results over the temperature range of interest. The SAC composite exhibits sufficient microwave absorption from 20 °C to approximately 600 °C owing to the superior dielectric properties of non-volatile mercury-containing compounds (HgCl₂ and HgS). At temperatures above 600 °C, the dielectric properties of the SAC are determined by the residual mercury and carbon matrix. Phase analyses indicate that the entire process of microwave heating could be divided into three stages: (1) The volatilization temperature of unbound water and some impurities are between 20 °C and 100 °C; (2) The main thermal disintegration region of mercury species is between 100 °C and 600 °C; (3) HgCl₂ and HgS volatilize completely to gas at 600 °C. Meanwhile, HgCl₂ decomposing more readily than HgS.     

掺氮石墨烯-铜基催化剂的制备及催化性能

采用水热法合成掺氮石墨烯(N/GN),通过超声辅助等体积浸渍法制备掺氮石墨烯-铜基催化剂(Cu-N/GN)。通过XRD、SEM、TEM、N2吸附脱附、XPS和XAES对催化剂的微观结构、形貌及元素组成进行表征,并考察Cu-N/GN对乙炔氢氯化反应的催化性能。结果表明:在催化剂中铜颗粒尺寸较小、均匀分布于N/GN片层上,且铜含量较低(3.6%);Cu-N/GN对乙炔氢氯化反应的催化效果良好,乙炔转化率为68%,氯乙烯选择性为99%。     

One-pot synthesis of nitrogen and sulfur co-doped activated carbon supported AuCl3 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℃ 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.     

Preserved in a Shell: High‐Performance Graphene‐Confined Ruthenium Nanoparticles in Acetylene Hydrochlorination

The potential implementation of ruthenium‐based catalysts in polyvinyl chloride production via acetylene hydrochlorination is hindered by their inferior activity and stability compared to gold‐based systems, despite their 4‐fold lower price. Combining in‐depth characterization and kinetic analysis we reveal the superior activity of ruthenium nanoparticles with an optimal size of 1.5 nm hosted on nitrogen‐doped carbon (NC) and identify their deactivation modes: 1) nanoparticle redispersion into inactive single atoms and 2) coke formation at the metal sites. Tuning the density of the NC carrier enables a catalytic encapsulation of the ruthenium nanoparticles into single layer graphene shells at 1073 K that prevent the undesired metal redispersion. Finally, we show that feeding O₂ during acetylene hydrochlorination limits coke formation over the nanodesigned ruthenium catalyst, while the graphene layer is preserved, resulting in a stability increase of 20 times, thus rivalling the performance of gold‐based systems.     

HgCl2(Caf): Co‐crystallization of Mercuric Chloride and Caffeine

Colourless single crystals of the co‐crystallizate of mercuric chloride and caffeine, HgCl₂(Caf), were obtained from an ethanolic solution of mercuric chloride, HgCl₂, and caffeine (Caf) and recrystallized from hot water. The crystal structure (monoclinic, P2₁, Z = 2, a = 398.36(8), b = 1964.5(4), c = 809.6(2) pm, β = 99.24(3)°, Z = 2, R₁ = 0.0584 for 1430 F_o > 4σ(F_o)) contains helical chains (parallel to the 2₁ screw axis) of almost unaffected HgCl₂ molecules and caffeine molecules which are very weakly bound to one keto‐oxygen atom (O4) of one and N9 of a second caffeine molecule at distances of 282 and 281 pm, respectively. To the contrary, theoretical calculations show that the molecule HgCl₂(Caf)₂ is stable (in the gas phase at T = 0 K) with surprisingly strong bonding as indicated by the “tetrahedrization” of the molecule.     

Etude des composés d'addition des acides de LEWIS XXVII. Composés d'addition de la cyclohexanedione-1, 4 avec HgCl2, ZnCl2, et TiCl4

The adducts of cyclohexane-1,4-dione with HgCl₂, ZnCl₂, and TiCl₄ have been prepared, and the IR. absorption spectra of the solid products studied. The lowering of the carbonyl frequency shows that the acceptor is linked by dative bonds to the carbonyl oxygen donors. This result confirms the cyclohexane-1,4-dione · HgCl₂ structure which has been determined by X rays diffraction.     

Kinetics and mechanism of catalytic acetylene hydrochlorination with gaseous HCl on the surface of mechanically activated K<Subscript>2</Subscript>PdCl<Subscript>4</Subscript>

The catalyst for acetylene hydrochlorination with gaseous HCl at room temperature is prepared by mechanical pretreatment of K₂PdCl₄ in an acetylene atmosphere. The rate-determining step of the reaction is the chloropalladation of π-coordinated acetylene involving an HCl molecule. As a consequence, the replacement of HCl with DCl brings about a kinetic isotope effect of 2.8 ± 0.4, which differs substantially from that observed in the protodemetalation of the intermediate palladium(II) chlorovinyl derivative yielding vinyl chloride (6.8 ± 0.6).     

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

We synthesized a S doped Bi/AC catalyst for acetylene hydrochlorination. The addition of H₂SO₄ changes the structure of the Bi atoms in the catalyst, resulting in the improvement of the specific surface areas and catalytic efficiency of the Bi-based catalyst under reaction conditions.     

SC-IrO2NR-carbon hybrid: A catalyst with high electrochemical stability for oxygen reduction

The enhanced electrochemical stability of the synthesized hybrid catalyst has been demonstrated by the introduction of the synergistic effect between carbon powder additive and the prepared catalyst.Single crystal IrO 2 nanorod (SC-IrO 2 NR) catalyst was prepared by a sol-gel method.The structure and performance of the catalyst sample were characterized by X-ray diffraction spectroscopy (XRD),scanning electron microscope (SEM),transmission electron microscope (TEM),rotating disk electrode (RDE) and cyclic voltammetry (CV) measurements.XRD patterns and TEM images indicate that the catalyst sample has a rutile IrO 2 single crystal nanorod structure.The onset potential for oxygen reduction reaction (ORR) of the SC-IrO 2 NR-carbon hybrid catalyst specimen is 0.75 V (vs.RHE) in RDE measurement.CV and RDE test results show that the SC-IrO 2 NR-carbon hybrid catalyst has a better electrochemical stability in comparison with the commercial Pt/C catalyst,with attenuation ratios of 17.67% and 44.60% for the SC-IrO 2 NR-carbon hybrid catalyst and the commercial Pt/C catalyst after 1500 cycles,respectively.Therefore,in terms of stability,the SC-IrO 2 NR-carbon hybrid catalyst has a promising potential in the application of the proton exchange membrane fuel cell.     

Uptake of inorganic Hg by organically modified silicates: influence of pH and chloride concentration on the binding pathways and electrochemical monitoring of the processes

Transport of mercury species in aquatic media is strongly affected by sorption processes on both organic and inorganic particles, and such mass transfer reactions are governed by speciation of this contaminant in the environment. The present research investigates the uptake of inorganic Hg^II species by sorbent materials based on polysiloxane-immobilized amine or thiol ligands, with the goal to highlight the effect of speciation on the sorption processes. Mercury binding was studied as a function of pH and chloride concentration to cover a wide range of species, including some among the most widely encountered forms in natural medium (HgCl₄²⁻, HgCl₃⁻, HgCl₂, Hg(OH)₂). It was found on the one hand that all these species are liable to be removed from solution by strong binding to silica gels grafted with mercaptopropyl groups. On the other hand, the use of silica bearing aminopropyl moieties has led to the selective accumulation of anionic chloro-complexes of Hg^II in acidic medium in the presence of high chloride concentration and to the uptake of Hg^II hydroxide around neutral pH, while HgCl₂ cannot be adsorbed on this material. The former reaction involves electrostatic interactions between HgCl₄²⁻ or HgCl₃⁻ and the ammonium form of polysiloxane-immobilized amine ligands, and the latter is driven by complexation of Hg^II species to the unprotonated amine groups. The interest of electrochemistry at carbon paste electrodes modified with these adsorbents for characterizing the sorption processes was also described by applying the following sequence “voltammetric detection subsequent to open-circuit accumulation”. This approach allows the in situ determination of the amount of mercury in the organic-inorganic hybrid phase, as a function of speciation in solution and without significant modification in the solution-phase concentrations, so that the adsorption and ion-exchange isotherms can be obtained very easily and without requiring additional treatment of the solid material.     

Hydrochlorination of unsaturated compounds by the action of CH2Cl2 or CHCl3 and rhodium complexes

A new method has been developed for the catalytic hydrochlorination of olefins and acetylenes in the presence of Rh complexes by means of HCl generated in situ from CH₂Cl₂ and CHCl₃ under the reaction conditions. The reaction was studied using the hydrochlorination of propylene, 1-hexene, 1-nonene, vinyl-cyclopropane, 1,1-dicyclopropylethylene, cyclohexene, cyclooctene, norbornene, and 1,5-cyclooctadiene as examples.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1373–1377, June, 1991.