Influence of the preparation method on the activity of phosphate-containing CoMo/HMS catalysts in deep hydrodesulphurization

Phosphate-containing hexagonal mesoporous silica (P/HMS) materials were used as supports of hydrotreating CoMo catalysts. Two series of catalysts were prepared by sequential and simultaneous impregnation of P/HMS substrates with cobalt and molybdenum salts solutions. Both bulk and surface structures of calcined and sulphided samples were determined by several techniques (SBET, XRD, UV–vis, TPD-NH3, TPR, FTIR of adsorbed NO and pyridine, HRTEM and XPS). The activity of P-containing CoMo catalysts was examined in hydrodesulphurization (HDS) of dibenzothiophene (DBT) and compared to that of a conventional commercial CoMo/Al2O3 catalyst. It was found that the dispersion of oxide and sulphide Co and Mo species depends on the presence of phosphate and also on the sequence of Co and Mo incorporation being co-impregnation more favourable than sequential impregnation. HRTEM analysis of sulphided samples (673 K) showed that larger stacking degree of MoS2 phase and better dispersion of Co and Mo species are achieved by co-impregnation. Activity tests revealed that sequential incorporation of Mo and Co is less effective for S-removal from DBT than co-impregnation. Contrary to sequential impregnation, the presence of P2O5 (up to 1.5 wt.%) on support surface enhanced S removal from DBT on the catalysts prepared by co-impregnation but the selectivity in this reaction was not influenced by phosphate and catalyst's preparation method. A close parallelism between active phase surface exposure and catalytic response was found.

Hexagonal mesoporous silica (HMS) containing a 1.5 wt.% P2O5 was selected as a substrate to deposit cobalt and molybdenum oxide precursors by sequential and co-impregnation methods. The sulphide catalysts were tested in DBT HDS and the series prepared by co-impregnation was substantially more active than that prepared by sequential impregnation. Figure optionsDownload as PowerPoint slide