Removal of refractory S-containing compounds from liquid fuels over P-loaded NiMoW/SBA-16 sulfide catalysts

P-containing SBA-16 mesoporous systems were used as supports of ternary Ni–Mo–W hydrodesulfurization (HDS) catalysts. The samples were characterized by a variety of techniques (N2 adsorption–desorption isotherms, XRD, TPR, TPD-NH3, DRS UV–vis and HRTEM). XRD profiles evidenced the formation of crystalline Mo1-xWxO3 and NiMoO4 phases on the surface of oxide catalyst precursors with high P-loadings (1.0 and 1.6 wt.%). The UV–vis DRS measurements showed a substantial decrease of energy band gap after P-loading onto the SBA-16 substrate with respect to P-free sample. The sulfided catalysts were tested in separate HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) reactions performed in a batch reactor at 320 °C and H2 pressure of 5.0 MPa. For both HDS reactions, the initial catalyst activity displayed a volcano-type curve indicating that catalyst behavior depends strongly on the phosphorous loading being all catalysts more active in the HDS of DBT then in the HDS of 4,6-DMDBT. The NiMoW/SBA-16 catalyst loaded with optimized amount of phosphorous (1.0 wt.%) showed superior initial activity than the P-free counterpart. This effect was attributed to the enhancement of active phases dispersion on the support surface, as revealed by HRTEM measurements. It was found that the formation of “onion-type” Mo(W)S2 phases on the catalyst surface was detrimental for the HDS activity. At reaction time of 5 h, the most active NiMoW/SBA-16 catalyst loaded with 1.0 wt.% of P showed similar activity in both HDS of DBT and 4,6-DMDBT reactions. It was found that HYD route of both reactions was promoted by the support modification with P and due to inhibition of coordinatively unsaturated sites (CUSs) by competitive adsorption of products (mainly H2S).