Controllable Synthesis of Vacancy-Defect Cu Site and Its Catalysis for the Manufacture of Vinyl Chloride Monomer

Asymmetric Ru-In atomic pairs promote highly active and stable acetylene hydrochlorination

Ru single-atom catalysts have great potential to replace toxic mercuric chloride in acetylene hydrochlorination. However, long-term catalytic stability remains a grand challenge due to the aggregation of Ru atoms caused by over-chlorination. Herein, we synthesize an asymmetric Ru-In atomic pair with vinyl chloride monomer yield (>99.5%) and stability (>600 h) at a gas hourly space velocity of 180 h-1, far surpassing those of the Ru single-atom counterparts. A combination of experimental and theoretical techniques reveals that there is a strong d-p orbital interaction between Ru and In atoms, which not only enables the selective adsorption of acetylene and hydrogen chloride at different atomic sites but also optimizes the electron configuration of Ru. As a result, the intrinsic energy barrier for vinyl chloride generation is lowered, and the thermodynamics of the chlorination process at the Ru site is switched from exothermal to endothermal due to the change of orbital couplings. This work provides a strategy to prevent the deactivation and depletion of active Ru centers during acetylene hydrochlorination.

Dual-vacancies modulation of 1T/2H heterostructured MoS2-CdS nanoflowers via radiolytic radical chemistry for efficient photocatalytic H2 evolution

Precise defect engineering of photocatalysts is highly demanding but remains a challenge. Here, we developed a facile and controllable γ-ray radiation strategy to assemble dual-vacancies confined MoS2-CdS-γ nanocomposite photocatalyst. We showed the solvated electron induced homogeneous growth of defects-rich CdS nanoparticles, while the symbiotic •OH radicals etched flower-like 1T/2H MoS2 substrate surfaces. The optimal MoS2-CdS-γ exhibited a H2 evolution rate of up to 37.80 mmol/h/g under visible light irradiation, which was 36.7 times higher than that of bare CdS-γ, and far superior to those synthesized by hydrothermal method. The microscopic characterizations and theoretical calculations revealed the formation of such unprecedented dual-sulfur-vacancies ensured the tight interfacial contact for fast charge separation. Besides, the existence of 1T-MoS2 phase further improved the conductivity and strengthened the adsorption interaction with H+ intermediate. Therefore, the radiolytic radical chemistry offered a facile, ambient and effective synthetic strategy to improve the catalytic performances of photocatalytic materials.

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.

Noble Metals Dissolution Catalyzed by [AlCl4 -]-Based Ionic Liquids

Imidazolium-based ionic liquid mixtures with [NO₃]^- and [AlCl₄]^- anions were used as oxidizing agents for the dissolution of Au, Pd, and Pt metals under mild conditions. The thermodynamic reduction of [NO₃]^- to [NO] is catalyzed by [AlCl₄]^- anions and coupled with the oxidation process of noble metals. The developed ionic liquid system for dissolving Au can reactivate the Au⁰ formed in the deactivation process of the catalyst in vinyl chloride production. This demonstrates the relevance of the here-presented work for technical noble metal recycling.

Migration: A Neglected Potential Contribution of HCl-Oxidized Au(0)

In this study, the typical oxidation process of Au/C catalysts exposed to HCl is presented. Although the process violates the standard electrode potentials, the "oxidized" tendency of Au(0) species is analyzed. This oxidation behavior can only be triggered over the Au/C sample within residual cationic Au species, and terminated over the completely metallic Au(0)/C sample. This study demonstrates that the presence of surface chlorination species cannot facilitate the oxidation of Au(0) and Au(I) when the sample is treated with HCl alone, which excludes the oxidation paths of: Au(0) → Au(III) and Au(I) → Au(III). The reported "HCl-oxidized Au(0)" behavior is partially caused by the migration of Au(III) species in the carbon bulk-phase, which occurs outside the XPS detection limit region and into the detection limit rather than the "HCl-oxidized Au(0)" itself. The mechanism of driving the bulk-phase Au(III) migrated from the steady destabilized state to the carbon surface is then studied. This study demonstrates that the migration of Au cannot be neglected behind the curious oxidation phenomenon by HCl, which provides a new perspective for the oxidation of other noble metals by HCl.

The Pincer Ligand Supported Ruthenium Catalysts for Acetylene Hydrochlorination: Molecular Mechanisms from Theoretical Insights

Pincer ligand supported RuII chloride complexes may be used for acetylene hydrochlorination as non-mercury molecular catalysts. Based on theoretical calculations, the catalytic mechanism and the interaction between catalysts and reactants has been evaluated, indicating that the (pincer)RuIICl2 platform supports electrophilic proton-ruthenation of C2H2. Energy decomposition studies further illustrate the electron-rich property of the RuII center, which can increase the negative charge of C2H2 via 4d-electron backdonation. Thus, the electrophilic reaction mechanism is favored due to lower energetic barriers. By improving the electron-donating ability of ligands, this lowering of energetic barriers can be enhanced. Therefore, non-mercury catalysts for acetylene hydrochlorination with milder reaction conditions and higher catalytic activity can be designed.

Deactivation Mechanism and Regeneration of the CuCl/Activated Carbon Catalyst for Gas-Solid Acetylene Dimerization

Acetylene dimerization is necessary to the coal chemical industry for producing monovinylacetylene, while the deactivation mechanism and regeneration of catalysts have not been studied in detail, which is crucial to the design of high-efficiency catalysts for acetylene dimerization. Herein, the deactivation mechanism and regeneration methods of CuCl/activated carbon catalysts in gas-solid acetylene dimerization were studied in detail. The catalysts with different reaction times were analyzed by temperature-programmed desorption of ammonia (NH₃-TPD), Fourier transform infrared (FT-IR), thermogravimetry (TG), pyridine-FTIR, and X-ray photoelectron spectroscopy (XPS) analyses. NH₃-TPD results demonstrated that as the time went on, the strong acid in the samples was enhanced, while the weak acid was weakened. Similarly, pyridine-FTIR results indicated that both Brönsted and Lewis acids in the samples were decreased. TG and XPS results showed that the reasons for deactivation for acetylene dimerization in the gas-solid reaction were significantly affected by coke deposition and the change of Cu valence. The more the content of Cu⁺, the higher the acetylene conversion rate, implying that Cu⁺ may be the active center of the acetylene dimerization reaction. Thus, removing carbon deposition through calcining and increasing the content of Cu⁺ was an effective way of regenerating the catalyst. This work strengthened the understanding of the deactivation behavior and provides a practicable regeneration method for the catalyst in gas-solid acetylene dimerization.

Catalytic Behavior of Au Confined in Ionic Liquid Film: A Kinetics Study for the Hydrochlorination of Acetylene

A systematic study of the kinetics of supported-ionic-liquid-phase (SILP) Au catalysis (Au-IL/AC) has been established in the continuous gas-phase hydrochlorination of acetylene. We reveal that the effect of ionic liquid (IL) film on substrate diffusion can be eliminated. The reaction order of the catalyst indicates that Au is confirmed to exist as a monomer in the IL film of the Au-IL/AC system, which is different from the fast equilibrium of the “Au dimer and monomer” for the classical Au/AC catalyst. The homogeneous reaction micro-environment is confirmed for Au-IL/AC since the activation energy was little changed under both heterogeneous and homogeneous catalysis, further verifying the monatomic characteristics of Au in Au-IL/AC. Due to the supported IL film, the reaction order of hydrogen chloride was decreased from 1 to 0.5 while creating a hydrogen chloride enrichment system around Au, which provides the possibility of producing vinyl chloride with an equal substrates feed ratio. This kinetic-perspective-based revelation of the catalytic behavior of the metal active sites confined in IL film enriches and expands the SILP catalytic system for acetylene hydrochlorination.

The reaction mechanism of acetylene hydrochlorination on defective carbon supported ruthenium catalysts identified by DFT calculations and experimental approaches

The electron density of ruthenium ions in RuCl3/AC-D catalyst increases, which reduces the energy barrier of the main reaction and inhibits the side reactions.