The effect of cobalt addition to bulk MoP and Ni 2P catalysts for the hydrodesulfurization of 4,6-dimethyldibenzothiophene

Abstract

Bulk metal phosphide catalysts with nominal composition Co x Ni 2P ( 0 ⩽ x ⩽ 0.34 ) and Co 0.07MoP were investigated for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) at 583 K and 3.0 MPa H 2. The selectivity for the direct desulfurization (DDS) of 4,6-DMDBT to the product dimethylbiphenyl (DMBP) increased to 49 and 31% over the Co 0.08Ni 2P and Co 0.07MoP catalysts, respectively, compared with the <3% DMBP selectivity obtained on bulk Ni 2P and MoP. Analysis by X-ray photoelectron spectroscopy (XPS) showed that the addition of the Co to MoP and Ni 2P resulted in a P enrichment of the catalyst surface. Among the Co x Ni 2P and Co 0.07MoP catalysts studied, the maximum DMBP selectivity occurred for the Co 0.08Ni 2P catalyst; this catalyst had the highest n-propylamine uptake and lowest CO uptake and the highest P/metal atom ratio, as determined by XPS. The increased selectivity to DMBP suggests that acid sites associated with phosphorous promote skeletal isomerization of 4,6-DMDBT to yield products that readily undergo DDS on the metal sites of the Co x Ni 2P ( 0 ⩽ x ⩽ 0.34 ) and Co 0.07MoP catalysts.