Metal-organic framework-derived cobalt and nitrogen co-doped porous carbon with four-coordinated Co-N-x for efficient acetylene hydrochlorination

Industrial production of vinyl chloride through acetylene hydrochlorination is a dominating technique in coal-rich areas, but its development is severely restricted by the use of toxic mercury chloride (HgCl2) catalyst. Inspired by the fact that doped carbon materials active in acetylene hydrochlorination often have good performance in the oxygen reduction reaction, a series of cobalt and nitrogen co-doped porous carbon catalysts prepared by pyrolysis of bimetallic ZIFs based on ZIF-8 and ZIF-67 under N-2 were applied in acetylene hydrochlorination. The catalytic activities of the co-doped catalysts varied with Co addition, and the highest acetylene conversion could be up to 83% with a space velocity of 2.6 ml g(-1) min(-1) at 220 degrees C when a small amount of cobalt was introduced. Results of several characterizations confirmed the existence of Co-N-x in the co-doped carbons, pointing out that this coordination structure makes the catalysts have better ability to adsorb and activate C2H2. Density functional theory calculation finally proved that C atom adjacent to the N atom in Co-N-4 structure is the primary active site in co-doped catalysts with high activity. We also conclude that the decreased N content caused by Co2N decomposition and the coordination structure change of Co-N-x should be responsible for the gradually worsening performances of the carbon catalysts with further Co addition. Our study provides a new route for improving the performance of N-doped carbon material in acetylene hydrochlorination and thus enhances its potential for practical application.