Environmentally friendly high-efficient metal-free catalyst for acetylene hydrochlorination derived from walnut shell-based N-doped biochar

Mercuric chloride as main catalyst for acetylene hydrochlorination poses a serious hazard to the environment due to its easily volatilizing and highly toxic characteristics. Mercuric-free catalysts, especially metal-free catalysts, are quite intriguing in the industrial production of acetylene hydrochlorination. In this work, nitrogen-doped biochar is prepared as green metal-free catalyst for acetylene hydrochlorination with natural walnut shells as starting material, in which the condensation product of dicyandiamide or dicyandiamide-formaldehyde is applied as nitrogen source. The 2.5DF/BC-850 catalyst exhibits superior catalytic activity with C2H2 conversion of 94.5% at 220°C and 45 h−1, which is attributed to the high content of quaternary nitrogen as active center. The introduction of formaldehyde effectively inhibits the carbon deposition in the catalytic reaction and improves the thermal stability of metal-free nitrogen-doped biochar catalyst. This work provides a significant insight into the design of environmentally friendly metal-free nitrogen-doped biochar catalysts for acetylene hydrochlorination.