Improved NiMoSA catalysts: Analysis of EDTA post-treatment in the HDS of 4,6-DMDBT

Abstract

Abstract To optimize the performance of HDS catalysts prepared with an improved support and a chelating agent, the present work analyzes the variations in HDS activity and hydrogenation/desulfurization selectivity when different protocols are applied in the preparation of a NiMo HDS catalyst with EDTA as chelating agent and silica-modified alumina (SA) as support. It was shown that grafting 6 wt. % SiO2 on the alumina support favors the formation of Mo6+Oh and decreases the presence of Mo6+Td, which is difficult to reduce and sulfide, resulting in SA supported catalysts with increased HDS activity. The use of both SA and EDTA improves the hydrogenation rate constant and not the direct desulfurization one. Successive impregnation Ni+Mo (Mo first) leads to higher dispersion of edge sites in the MoS2 crystallites. Post-treatment of the oxide catalysts with EDTA gives rise to a better promotion associated to the removal of Ni from inactive compounds, favoring additional formation of NiMoS phase. The post-treatment is more effective in catalysts prepared by successive impregnation. The successively-prepared EDTA+Ni+Mo/SA catalyst presents the highest activity in the HDS of 4,6-DMDBT.