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

Abstract

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 m² 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 ${\text{mol}}{}_{{\text{Cl}}}^{ - 1}$ 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.