Analysis of the promotion of CoMoP/Al2O3 HDS catalysts prepared from a reduced H–P–Mo heteropolyacid Co salt

HDS activity of 4,6-DMDBT for calcined and non-calcined CoMoP/Al2O3 catalysts prepared with Co7/2PMo12O40 was compared with that of a catalyst prepared conventionally by coimpregnation with a solution containing ammonium heptamolybdate, cobalt nitrate, and phosphoric acid. The extent of promotion for each method of preparation was quantitatively determined by CO adsorption, and the intrinsic activity of the different coordinatively unsaturated Mo sites in the catalyst was evaluated. The use of Co7/2PMo12O40 as catalyst precursor leads to higher HDS activity than the catalyst prepared by coimpregnation. The high activity of the former catalyst was related to a higher number of Co-promoted molybdenum sites. The number of Co-promoted sites depends on the pretreatment before sulfidation, particularly calcination. Highest activity is obtained by avoiding calcination, and the activity decreases with the calcination temperature. Two different types of promoted CoMoS sites with different HDS intrinsic activities seem to coexist in the sulfided catalyst.

Graphical abstractThe number of Co-promoted sites in CoMoP/Al2O3 HDS catalyst prepared with Co7/2PMo12O40 depends on the pretreatment given to the catalyst before its activation (sulfidation). Two different types of promoted CoMoS sites with different HDS intrinsic activities seem to co-exist in the sulfided catalyst.Figure optionsDownload full-size imageDownload high-quality image (165 K)Download as PowerPoint slideHighlights► The promotion degree for CoMoP HDS catalysts prepared differently was analyzed and quantified. ► The use of a Co heteropolyacid salt as catalyst precursor renders high promotion and HDS activity. ► Two types of active CoMoS sites were detected by CO adsorption. ► Maximum HDS activity was obtained avoiding the calcination step in the preparation of the catalyst.