Preparation Of Metal Phosphides By Hydrogen Plasma Reduction And Their Catalytic Performance In Hydrodesulfurization

Transition metal phosphides are attractive candidates for high-performance catalytic, electronic, and magnetic applications. A variety of methods can be used to synthesize bulk metal phosphides. Amoung them, temperature programmed reduction (TPR) of metal phosphates at high temperature was generally feasible for the preparation of supported transition-metal phosphides for using as hydrotreating or hydrogenation catalysts, but the particles were always aggregated, and phosphorus loss occured at high reduction temperature. In this paper, we describe a new strategy for synthesizing metal phosphides (Ni2P, CoP, MoP and WP) that using nonthermal hydrogen plasma as the reduction medium instead of the H2 used in the TPR method, and the HDS acitivity of DBT and 4,6-DMDBT was evaluated. XRD, CO chemisorption, TPR, HRTEM, SEM, ICP-AES techniques were used to characterize the structures of the metal phosphides. The mechanism of phosphide preparation with PR method was also speculated.Bulk metal phosphides were prepared with PR method, the effect of voltage, reduction time, M/P ratio and doping of noble metal on the phosphide phase formation were investigated. The results told that under higher voltage, longer reduction time, the phosphides were better crystallized. For MoP and WP, the M/P ratio influenced the crystallization, while for Ni2P and CoP, it determined phase of the phosphide. The reduciton voltage of oxidic precursors could be lower down by co-impregnation of Ru; InP, GaP, Fe2P were also be prepared by hydrogen plasma method (PR).Transition metal phosphides (Ni2P, CoP, MoP, WP) were prepared by TPR and PR method, the HDS performance was also compared. The influence of the M/P ratio, voltage and passivation method on the HDS performances of the phosphides prepared with PR method was examined. The results indicated that catalysts prepared by PR method showed higher DBT HDS activity then TPR method. And the activity of phosphides prepared by PR method was in the following order:CoP>Ni2P>MoP≈WP。CoP was more difficult to be prepared then MoP, N12P and WP, and Co2P which owned low HDS activity could easily formed, so the activity of CoP prepared by TPR method showed lower HDS activity. Better crystallised and high HDS performance CoP could be prepared with lower reduction voltage by doping oxidic CoP with Ru, the particle size of CoP was smaller and CoP phase was not changed.The phosphides catalysts:MoP/MCM-41, WP/MCM-41 and Ni2P/MCM-41, were prepared by four methods. The HDS activity was in the following order:WP>MoP>Ni2P, WP and MoP mainly through direct hydrodesulfurization path, while direct hydrodesulfurization mainly happened on Ni2P. The mechanically mixed of them were evaluated in simultaneously HDS of DBT and 4,6-DMDBT. The results showed that there was synergistic effect between WP+Ni2P/MCM-41 which exhibited best performance; the hydrodesulfurization activity was in the following order:SR>PR>MR>>IP.