Silicon carbide-derived carbon nanocomposite as a substitute for mercury in the catalytic hydrochlorination of acetylene

Abstract

Acetylene hydrochlorination is an important coal-based technology for the industrial production of vinyl chloride, however it is plagued by the toxicity of the mercury chloride catalyst. Therefore extensive efforts have been made to explore alternative catalysts with various metals. Here we report that a nanocomposite of nitrogen-doped carbon derived from silicon carbide activates acetylene directly for hydrochlorination in the absence of additional metal species. The catalyst delivers stable performance during a 150 hour test with acetylene conversion reaching 80% and vinyl chloride selectivity over 98% at 200°C. Experimental studies and theoretical simulations reveal that the carbon atoms bonded with pyrrolic nitrogen atoms are the active sites. This proof-of-concept study demonstrates that such a nanocomposite is a potential substitute for mercury while further work is still necessary to bring this to the industrial stage. Furthermore, the finding also provides guidance for design of carbon-based catalysts for activation of other alkynes.

Enhancement of Au/AC acetylene hydrochlorination catalyst activity and stability via nitrogen-modified activated carbon support

“…2a, NAC1 catalysts display very poor catalytic activity (5% conversion) for acetylene hydrochlorination reaction, while no conversion was detected in AC1. In fact, experimental studies and theoretical simulations revealed that the carbon atoms bonded with pyrrolic nitrogen atoms are the active sites have been reported by Bao's group before [26].…”

“…6c indicates that there is a considerable amount of acetylene desorption which covers the temperature range of 50-300°C, higher than the reaction temperature (180°C), validating the capability of NAC1 for activating acetylene directly and in line with the fact that NAC1 exhibits some activity for the hydrochlorination process. DFT study also shows that the nitrogen doping enhanced the formation of the covalent bond between C 2 H 2 and NCNT compared with the undoped CNT, and therefore promoted the addition reaction of the C 2 H 2 and HCl into C 2 H 3 Cl [26][27][28]. After a deposition of 1 wt.% Au onto the AC1 and NAC1 support, a new C 2 H 2 desorption peak appears at 250°C.…”

“…Indeed, as reported before, doping carbon with nitrogen atoms has been demonstrated to be an effective approach to tune its catalytic activities [43]. For instance, experimental studies and density functional theory (DFT) calculations revealed that the carbon atoms close to pyrrolic nitrogen are the main active sites among the different nitrogen doping configurations in the hydrochlorination of acetylene [26]. In addition, recent observations suggest that carbon-based catalyst support materials can be systematically doped with nitrogen to create strong, beneficial catalyst-support interactions by increased support/catalyst chemical binding (or anchoring) which substantially enhances catalyst activity and stability [44].…”

“…Furthermore, the presence of nitrogen atoms in the carbonaceous material tailors their surface properties accordingly, supporting a new idea to employ it as one active substrate for mercury-free hydrochlorination. For example, Bao's group [25,26] and others [27,28] have shown that carbon nitrides can be chemically shaped to a variety of nanostructures, and can catalyze directly transformation of acetylene to vinyl chloride. However, their use on an industrial scale is restricted by the lower activity, and hence limits the production capacity and leads to difficult purification.…”

The Preparation of Cu-g-C3N4/AC Catalyst for Acetylene Hydrochlorination

“…A previous investigation by our group demonstrated that pyrrolic N ranked first in the order of nitrogen species' role for this reaction [19]. Bao et al also reported, based on experimental and theoritical results, that pyrrolic N in carbon is the active site for acetylene hydrochlorination [20]. Therefore, the pyrrolic N content of the Cu-g-C 3 N 4 /AC catalyst increased relative to that of the g-C 3 N 4 /AC catalyst, which is consistent with the catalytic activity.…”