Non-mercury catalytic acetylene hydrochlorination over spherical activated-carbon-supported Au–Co(III)–Cu(II) catalysts

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.

Competing on the same stage: Ru-based catalysts modified by basic ligands and organic chlorine salts for acetylene hydrochlorination

To provide reference for the search of efficient ligands for acetylene hydrochlorination, various basic ligands with different alkaline gradients have been employed to modify Ru-based catalysts, and a rule is...

Construction of highly dispersed Au active sites by ice photochemical polishing for efficient acetylene hydrochlorination

Compared to traditional Au/AC, ice-photochemical polishing results in atomically dispersed AuClx-like multi-sites, yielding a significantly improved performance of Au/AC-F1I1 catalysts.

Ru supported on activated carbon and coated with a polydopamine layer for effective acetylene hydrochlorination

Ru/AC@PDA-T catalysts were synthesized by coating a protective layer of PDA derivatives on the Ru/AC catalyst. Significantly improved activity and stability provide directions for the development of environmentally friendly and economical catalysts.

A structured catalyst with high dispersity of Au species based on hollow SiC foam with porous walls for acetylene hydrochlorination

It is essential to improve the catalytic stability of Au-based catalysts for acetylene hydrochlorination. In this study, a novel hollow SiC foam with porous walls (HSFp) is proposed to modify the Au catalyst distribution on the foam-based structured catalyst. The scanning electron microscopy and 3D X-ray tomography results showed that the hollow structure and the porous ceramic wall of HSFp were successfully obtained. An Au/AC/HSF structured catalyst was prepared by the slurry-coating and impregnation method. Then the effects of the wall pore structure of HSFp on the distribution of Au species and the stability of the catalyst were studied by comparison with a hollow SiC foam with compact walls (HSFc). The HSFp with 3D interconnected hollow channel structure was demonstrated to have a promotion effect on the reaction stability due to its ability to refine the catalyst particles during the impregnation and drying processes. The result indicates that the time on stream of acetylene conversion above 90% over the Au/AC/HSFp structured catalyst reaches about 380 h at an acetylene gaseous hourly space velocity of 130 h-1, which is much longer than that of the Au/AC/HSFc. In addition, a bidirectional diffusion effect that can enhance the catalyst distribution by the porous wall of HSF was proposed in this paper. This may have positive significance in the field of preparation of structured catalysts.

Sulfur Promotion in Au/C Catalyzed Acetylene Hydrochlorination

The formation of highly active and stable acetylene hydrochlorination catalysts is of great industrial importance. The successful replacement of the highly toxic mercuric chloride catalyst with gold has led to a flurry of research in this area. One key aspect, which led to the commercialization of the gold catalyst is the use of thiosulphate as a stabilizing ligand. This study investigates the use of a range of sulfur containing compounds as promoters for production of highly active Au/C catalysts. Promotion is observed across a range of metal sulfates, non-metal sulfates, and sulfuric acid treatments. This observed enhancement can be optimized by careful consideration of either pre- or post-treatments, concentration of dopants used, and modification of washing steps. Pre-treatment of the carbon support with sulfuric acid (0.76 m) resulted in the most active Au/C in this series with an acetylene conversion of ≈70% at 200 °C.

A study on the rules of ligands in highly efficient Ru–amide/AC catalysts for acetylene hydrochlorination

The electron donor ability and steric hindrance of substituents on amide ligands jointly affect the modification effect of ligands on ruthenium based catalysts for acetylene hydrochlorination.

Progress and Challenges of Mercury-Free Catalysis for Acetylene Hydrochlorination

Activated carbon-supported HgCl2 catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl2 is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis of mercury-free and environmentally benign catalysts with high activity has become an urgent need for vinyl chloride monomer (VCM) production. This review summarizes research progress on the design and development of mercury-free catalysts for acetylene hydrochlorination. Three types of catalysts for acetylene hydrochlorination in the chlor-alkali chemical industry are discussed. These catalysts are a noble metal catalyst, non-noble metal catalyst, and non-metallic catalyst. This review serves as a guide in terms of the catalyst design, properties, and catalytic mechanism of mercury-free catalyst for the acetylene hydrochlorination of VCM. The key problems and issues are discussed, and future trends are envisioned.

Sulphur-doped activated carbon as a metal-free catalyst for acetylene hydrochlorination

A series of sulfur-doped spherical activated carbon (SAC) catalysts were prepared with phenyl disulfide (C12H10S2) as a sulfur source for acetylene hydrochlorination. The S-doped catalyst exhibits preferable catalytic performance compared to that of the blank carrier with the reaction conditions of GHSV of 90 h-1 and at 180 °C. The catalysts were characterized by N2 adsorption/desorption (BET), elemental analysis (EA), thermogravimetric analysis (TG), temperature-programmed desorption (TPD), Raman spectrum (Raman) and X-ray photoelectron spectroscopy (XPS). The results indicate that the presence of sulfur species is favorable to promote the ability of reactant adsorption and inhibit carbon deposition. In addition, the electronic and chemical properties of catalysts were investigated by density functional theory (DFT) simulation. It is illustrated that the introduction of sulfur species can not only change the spin density and charge density but also create more active sites on a carrier. The single sulfur doped carbon material catalysts were designed for the first time and the desirable results make it a green catalyst for the industrial application of acetylene hydrochlorination.

Demystifying the mechanism of NMP ligands in promoting Cu-catalyzed acetylene hydrochlorination: insights from a density functional theory study

Experimental results and DFT calculations revealed the promoting effect of NMP on catalytic reactivity and the inhibiting effect of NMP on the reduction of Cu²⁺ to Cu⁺ and Cu⁰, respectively.

Highly Active AuCu-Based Catalysts for Acetylene Hydrochlorination Prepared Using Organic Aqua Regia

Development of a sustainable process for designing and synthesising an active and stable catalyst for hydrochlorination of acetylene is challenging, yet crucial, for industrial vinyl chloride monomer (VCM) production. Herein, direct synthesis of bimetallic AuCu catalysts using organic aqua regia (OAR) preparation methods was investigated. In comparison with conventional aqua regia (AR), bimetallic AuCu catalysts synthesised from OAR exhibit enhanced activity and stability. After careful characterisation of the catalyst samples using X-ray diffraction patterns (XRD), Scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and Temperature-programmed desorption (TPD), this observation was justified for the following reasons: 1) the existence of sulphur and nitrogen atoms stabilised the cationic Au active sites, and 2) OAR helped to sustain the function of the Cu promotor by stabilising it. Advanced understanding on the importance of promoter stability has unveiled new perspectives for this research area.

Self- regeneration of Au/CeO2 based catalysts with enhanced activity and ultra-stability for acetylene hydrochlorination

Replacement of Hg with non-toxic Au based catalysts for industrial hydrochlorination of acetylene to vinyl chloride is urgently required. However Au catalysts suffer from progressive deactivation caused by auto-reduction of Au(I) and Au(III) active sites and irreversible aggregation of Au(0) inactive sites. Here we show from synchrotron X-ray absorption, STEM imaging and DFT modelling that the availability of ceria(110) surface renders Au(0)/Au(I) as active pairs. Thus, Au(0) is directly involved in the catalysis. Owing to the strong mediating properties of Ce(IV)/Ce(III) with one electron complementary redox coupling reactions, the ceria promotion to Au catalysts gives enhanced activity and stability. Total pre-reduction of Au species to inactive Au nanoparticles of Au/CeO₂&AC when placed in a C₂H₂/HCl stream can also rapidly rejuvenate. This is dramatically achieved by re-dispersing the Au particles to Au(0) atoms and oxidising to Au(I) entities, whereas Au/AC does not recover from the deactivation.

An efficient Au catalyst supported on hollow carbon spheres for acetylene hydrochlorination

Mesoporous hollow carbon spheres (HCS) were prepared and applied as the support of Au catalyst for acetylene hydrochlorination. Au/HCS exhibited excellent stability for acetylene hydrochlorination.

Facilitating CO2 Transport Across Mixed Matrix Membranes Containing Multifunctional Nanocapsules

Mixed matrix membranes (MMMs) have exhibited advantages in overcoming the trade-off effect, although it is still intensively demanded in the design of multifunctional fillers to improve CO₂ separation performance. At present, MMMs with transport channels present an effective strategy to obtain ultrahigh CO₂ permselectivity. In this work, Pebax-based MMMs was fabricated by incorporating nanocapsules (NCs), whose exterior, interior and transverse shell surfaces contained abundant carboxylic acid groups. NCs, similar to vesicles in cells, provide favorable physical and chemical microenvironments to the constructed CO₂ transport channels, enhancing the CO₂ permselectivity via both a facilitated transport mechanism and a solution-diffusion mechanism. CO₂ permselectivity of MMMs doped with 20 wt % NCs surpassed the 2008 Robeson limit; an increase in CO₂ permeability was up to 1431 ± 35 Barrer for pure gas, which was a 362% enhancement from the pure membrane, and an increase of the CO₂/CH₄ and CO₂/N₂ ideal selectivities to 46 ± 1.4 and 69 ± 2.7, corresponding to 44% and 23% enhancements from the pure membrane, respectively. This study provides an ingenious strategy to enhance the gas permselectivity of MMMs.

Gold nanocatalysts supported on carbon for electrocatalytic oxidation of organic molecules including guanines in DNA

Gold (Au) is chemically stable and resistant to oxidation. Although bulk Au is catalytically inert, nanostructured Au exhibits unique size-dependent catalytic activity. When Au nanocatalysts are supported on conductive carbon (denoted as Au@C), Au@C becomes promising for a wide range of electrochemical reactions such as electrooxidation of alcohols and electroreduction of carbon dioxide. In this mini-review, we summarize Au@C nanocatalysts with specific attention on the most recent achievements including the findings in our own laboratories, and show that Au nanoclusters (AuNCs, <2 nm) on nitrided carbon are excellent electrocatalysts for the oxidation of organic molecules including guanines in DNA. The state-of-the-art synthesis and characterization of these nanomaterials are also documented. Synergistic interactions among Au-containing multicomponents on carbon supports and their applications in electrocatalysis are discussed as well. Finally, challenges and future outlook for these emerging and promising nanomaterials are envisaged.

Acetylene in Organic Synthesis: Recent Progress and New Uses

Recent progress in the leading synthetic applications of acetylene is discussed from the prospect of rapid development and novel opportunities. A diversity of reactions involving the acetylene molecule to carry out vinylation processes, cross-coupling reactions, synthesis of substituted alkynes, preparation of heterocycles and the construction of a number of functionalized molecules with different levels of molecular complexity were recently studied. Of particular importance is the utilization of acetylene in the synthesis of pharmaceutical substances and drugs. The increasing interest in acetylene and its involvement in organic transformations highlights a fascinating renaissance of this simplest alkyne molecule.

Carbon-supported perovskite-like CsCuCl3 nanoparticles: a highly active and cost-effective heterogeneous catalyst for the hydrochlorination of acetylene to vinyl chloride

Non-mercuric catalysts in acetylene hydrochlorination reaction have been gained much attention.

Zn–Cu bimetallic catalysts supported on pure silica MCM-41 for acetylene hydration reaction

The addition of copper improved the activity and stability of Zn–Cu/MCM bimetallic catalysts and interacted synergistically with Zn species and prevented Zn species loss during the reaction.

Nitrogen doped nanoflower porous carbon as a nonmetal catalyst for acetylene hydrochlorination

The performance of nanoflower-like morphology NPC-T catalysts on acetylene hydrochlorination was related to the nitrogen content of species as well as specific surface area.

Study on non-isothermal kinetics of the thermal desorption of mercury from spent mercuric chloride catalyst

Kinetics of the thermal desorption of mercury from spent mercury chloride catalysts were investigated using non-isothermal thermal analysis technique. Complex mercury species absorbed on waste catalysts were revealed by sequential extraction procedure. A scheme of six reactions was applied to elucidate mercury desorption kinetics. Activation energy estimated by model-free isoconversional methods is a slightly increasing function of conversion, implying a variation in the mechanism controlling mercury desorption. Average value of apparent activation energy (116.32kJ/mol) calculated by isoconversional Starink method was used to determine reaction mechanism using model-fitting and z(α) master method. One dimensional diffusion appears to govern mercury desorption process in the conversion range of 10%-40%, and then the reaction kinetic is controlled by two and three dimensional diffusion at greater conversion.

Bi/AC modified with phosphoric acid as catalyst in the hydrochlorination of acetylene

Phosphorus-doped Bi/AC was prepared via a facile co-impregnation method and exhibited elevated catalytic performance.

Oxidation modification of Ru-based catalyst for acetylene hydrochlorination

Oxidation modification enhances the interaction between the oxygenated functional groups and Ru species, strengthens the adsorption of reactants, and augments the amount of active species, enhancing the catalytic performance of the catalysts.