The Influence of the Support on the Formation of Ni₂P Based Catalysts by a New Synthetic Approach. Study of the Catalytic Activity in the Hydrodesulfurization of Dibenzothiophene

Abstract

A series of novel, active and easily synthesized nickel phosphide catalysts were prepared by means of temperature-programmed reduction (TPR) of Ni(HPO3H)2, and the role of the support on Ni2P formation and catalytic activity was studied. For this purpose four catalysts with a nickel loading of 10 wt % were synthesized by using two mesoporous supports, MCM-41 and zirconium doped MCM-41 (MCM-SiZr), as well as two commercial supports, SiO2 (Cab-osil) and γ-Al2O3. The dibenzothiophene (DBT) hydrodesulfurization (HDS) activity was measured for these Ni2P based catalysts, displaying good activity. All catalysts reached high DBT conversion values at high temperatures, with the DDS (direct desulfurization) route being favored, i.e. yielding mainly biphenyl (BP). Silica supported catalysts, Ni2P-10 (Si) and Ni2P-10 (Cab), proved highly stable with time on stream (48 h) with conversion values close to 100%. More acidic supports provided lower conversion values and underwent deactivation. Thus, Ni2P-10 (Zr) catalyst only presents a constant conversion of 80% after 48 h of reaction, but when the support is γ-Al2O3 deactivation occurs. Further, the analysis of the spent catalyst revealed the presence of sulfur on the surface, possibly forming a phosphosulfide phase. A poor result is obtained with Ni2P-10 (Al), which undergoes deactivation with time on stream. This is due to both a lower proportion of the Ni2P phase being present on the surface and the possible formation of NiS under the reaction conditions used.