Activated carbon supported cobalt-molybdenum carbides: effect of the synthesis method, heating rate, type of cobalt precursor and presulfiding agent on thiophene hydrodesulfurization

Abstract

This work studied the Effect of the presulfiding agent, type of precursor (sulfate vs. nitrate of promotor), synthesis method (conventional vs. carbothermal carbiding) and heating rate in the hydrodesulfurization of thiophene over activated carbon supported cobalt-molybdenum carbides. The synthesis was carried out using the methods conventional (CH4/H2 (1:4)) and carbothermal with H2 at 973 K and 1 or 5 K/min. The carbided phases were characterized by surface area (B.E.T), X-ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The surface areas were within a rank of 266 and 493m2/g, whereas the XRD analysis verified the presence of Co6Mo6C2 for carbides obtained by carbothermal method independently of these variables. The XPS showed the presence on the surface of: Moδ+, Mo4+and Mo6+, and Co2+ whose abundance was influenced by the synthesis method and type of precursor. On the order hand, XPS revealed that the carbides obtained by sulfate precursor retained sulfur on the surface as S2- and SO42-. Tests of thiophene HDS showed that carbides obtained by the carbothermal method had higher activity than those obtained by the conventional method when it was activated with CS2/H2 and inversely when used H2S/H2.