Xiaoxia Di

Nitrogen-modified activated carbon supported bimetallic gold–cesium(I) as highly active and stable catalyst for the hydrochlorination of acetylene

In the challenging acetylene hydrochlorination to vinyl chloride over Au-based catalysts, Au–CsI catalysts are substantially more active and stable than their monometallic counterparts. Here we describe a novel nitrogen-modified activated carbon supported Au–CsI catalyst (1Au4CsI/NAC) that delivers stable performance for acetylene conversion reaching 90.1% and there was only 1.5% C2H2 conversion loss after 50 h under the reaction conditions of C2H2 hourly space velocity 1480 h−1. After a careful characterization of all the catalysts, we concluded that the nitrogen atoms’ influence on the stability of the Au–CsI catalysts correlates with the strengthening of the adsorption of hydrogen chloride to the catalyst and consequently inhibits Au3+ reduction under the reaction conditions.

Ultra-low Ru-promoted CuCl2 as highly active catalyst for the hydrochlorination of acetylene

Here we report a novel catalyst consisting of 400 ppm Ru and 4.24 wt% Cu supported on carbon nanotubes for the hydrochlorination of acetylene. We observed a synergy between Ru and Cu and obtained a highly active catalyst. The TOF of Cu400Ru/MWCNTs was higher than that of the HgCl2 catalysts.

Activated carbon supported ternary gold–cesium(I)–indium(III) catalyst for the hydrochlorination of acetylene

Commercialization of acetylene hydrochlorination using AuCl3 catalysts has been impeded by its poor stability. We have been studying CsCl as a promoter, which can improve acetylene hydrochlorination activity and has resistance to catalytic deactivation. InIII added to the Au–CsI/AC catalysts worked as efficient catalysts for the hydrochlorination of acetylene to vinyl chloride. A series of trimetallic catalysts (1AuxInIII4CsI/AC with x = 0.5, 1, 2, 3) were prepared and assessed for their ability to promote hydrochlorination of acetylene. The enhancement of stability observed for a Au/InIII/CsI weight ratio of 1:1:4 was particularly remarkable. It delivered stable performance within the conversion of acetylene, reaching more than 92.8%, and there was only 3.7% C2H2 conversion loss after running for 50 h under the reaction conditions of a temperature of 180 °C and a C2H2 hourly space velocity of 1480 h−1. Moreover, the 1Au1InIII4CsI/AC catalyst delivered stable performance with an estimated lifetime exceeding 6520 h at a C2H2 hourly space velocity of 50 h−1. H2-TPR, TEM, HCl-TPD, C2H2-TPD, XPS and TGA techniques were further applied to reveal the structural information on the Au–InIII–CsI/AC catalysts. The results reveal that the addition of InCl3 increased the electron density of Au3+ species via electron transfer from the In atoms to the Au3+ center which can increase the adsorption of hydrogen chloride and therefore improve the catalytic stability. These results demonstrate that the addition of metal additives CsCl and InCl3 results in a synergistic effect to enhance the activity and the stability of Au-based catalysts. The excellent catalytic performance of the 1Au1InIII4CsI/AC catalyst demonstrated its potential as an alternative to mercury chloride catalysts for acetylene hydrochlorination.

Supported ionic-liquid-phase-stabilized Au(III) catalyst for acetylene hydrochlorination

Using high-valent Au(III) catalysis is highly desirable in many reactions; however, it is plagued by the poor stability of Au(III) complexes. Still, conventional catalysts need high Au content makes the high price and demand for Au is one of the major obstacles limiting their large-scale application. Here we demonstrate that stable and catalytically active Au(III) complexes can be obtained using Supported Ionic Liquid Phase (SILP) technology. The resulting heterogeneous Au–IL/AC catalysts combine the advantages of the catalytic species being stabilised in the Au(III) form by forming a Au(III)–IL complex and the need for a less expensive metal catalyst because the active component can be better developed in a homogeneous reaction medium. When used in acetylene hydrochlorination reaction, this catalyst displayed an excellent specific activity and superior long-term stability. Under the same reaction conditions, the Au(III)–IL/AC catalyst shows higher activity and stability towards the vinyl chloride monomer (VCM) than IL-free Au/AC (C2H2 conversion = 72.1% at 180 °C compared to 16.1% without IL). It also delivered stable performance within the conversion of acetylene, reaching more than 99.4%, and there was only a 3.7% C2H2 conversion loss after running for 300 h under the reaction conditions of a temperature of 180 °C and a C2H2 hourly space velocity of 30 h−1. Its exceptional ability to maintain the high activity and stability further demonstrated the potential for the replacement of Hg-based catalysts for acetylene hydrochlorination.

Promotional effect of copper(II) on an activated carbon supported low content bimetallic gold–cesium(I) catalyst in acetylene hydrochlorination

The synthesis of a vinyl chloride monomer (VCM) from acetylene hydrochlorination is a highly attractive coal-based route using mercury chloride (HgCl2) as the catalyst. On reducing the use of mercury and with increasing concerns about environmental issues, searching for alternative catalysts has gained interest in recent years. However, to achieve high yield and stability using a mercury-free catalyst in this reaction is a substantial challenge. We approach this question by probing a Cu-added AuCs/AC catalyst working as a highly active, stable and cost-effective catalyst for this reaction. Introducing Cu into the catalyst significantly increased the activity and stability compared to a bicomponent AuCs/AC catalyst, underscoring a remarkable synergistic effect of the three metals. The particularly remarkable enhancement of activity was observed for the catalyst with a Au/Cu/Cs weight ratio of 1 : 1 : 4 (Au = 0.25 wt%), which provided a high turnover frequency of 73.8 min−1 based on Au. Further experiments showed that the AuCuCs/AC catalyst delivered a stable performance during a 600 h test with the conversion of acetylene maintaining more than 98.8% at a C2H2 gas hourly space velocity of 50 h−1 and the estimated lifetime exceeding 6540 h. After a careful characterization of the AuCuCs/AC catalyst and additional catalytic tests, we concluded that the observed enhanced catalytic performance could be associated with the enhanced dispersion of Au particles, the stabilization of Au in the state of Au3+ and facile substrate C2H2 molecule desorption. Compared with the commercial high content HgCl2 catalyst (Hg = 12 wt%), this low content AuCuCs/AC catalyst (Au = 0.25 wt%) has similar activity, higher stability, relative low cost and environmental friendliness, meaning it has potential as an alternative to the HgCl2 catalyst for commercial production of VCM.

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. Cu-based catalysts are low-cost, green and stable. However, their lower activity than that of mercury-based catalysts limits their practical applications. In this study, we report activated carbon-supported perovskite-like CsCuCl3 nanoparticles as a catalyst for hydrochlorination of acetylene. Cu–Cs/AC with 1 wt% Cu content exhibits superior activity than pure Cu/AC and even Hg/AC. At the condition of 200 °C and 50 h−1 industrial space velocity, C2H2 conversion is maintained at 92% over 200 h. Our findings suggest that the low-cost Cu–Cs/AC catalyst can be envisioned as a viable alternative to commercial toxic HgCl2 for acetylene hydrochlorination.