Gas-phase Hydrodechlorination of Chlorobenzene Over Silica-supported Ni2P Catalysts Prepared Under Different Reduction Conditions

摘要

The influence of reduction conditions on the properties and reactivity of silica-supported nickel phosphide (Ni2P/SiO2) catalysts for gas-phase hydrodechlorination (HDC) of chlorobenzene was investigated. The catalysts prepared under different reduction conditions had the similar specific surface area (～370 m~2 g~(-1)), and pore diameter (～5.2 nm) and Ni2P crystallites size (10-13 nm). However, comparing with Ni2P/SiO2 catalyst prepared at 923 K with the H2 space velocity of 15,000 mL g~(-1) h~(-1) for 2 h, with increasing the H2 space velocity from 15,000 to 19,200 mL g~(-1) h~(-1), or the reduction temperature from 923 to 1023 K or the reduction time from 2 to 6 h, the Ni/P ratio in the prepared catalyst was increased from 1/0.56 to about 1/0.50, and the HDC reaction induction period over the catalyst was also shortened from above 30 to 2-4 h. It is suggested that the induction period might be due to the blocking of active sites by excess phosphorus, which results in hindering the activation of chlorobenzene and the adsorption of hydrogen species on Ni2P. Under the conditions of 573 K and W_(Ni)/F_(Cl) = 186.6 g_(Ni) mol_(Cl)~(-1) min, the chlorobenzene conversion over the Ni2P/SiO2 catalyst reached 99%, and it did not change during 36 h. The good activity and stability of the Ni2P/SiO2 catalyst was ascribed to the weak interaction between chlorine and Ni2P and a great of spilt-over hydrogen species on the catalyst surface.