Enhanced catalytic activity of ultrasmall NiMoW trimetallic nanocatalyst for hydrodesulfurization of fuels

As the need of the hour, it is imperative to develop highly active HDS catalyst capable of desulfurizing refractory organic sulfur compounds (DBT; 4, 6 DMDBT etc.). In comparison to well established bimetallic catalysts (e.g. NiMo/NiW), trimetallic catalysts exhibit synergistic effect between active metal species which promotes both direct desulfurization (DDS) and hydrogenation pathway (HYD) and hence display higher catalytic activity. The synergistic effect is determined by the catalytically active amorphous phase formed due to partial substitution of Mo by W during synthesis of trimetallic nanocatalysts. This can be achieved by synthesizing the catalyst as ultrasmall size nanocatalysts. To this end, in the present study we report NiMoW trimetallic nanocatalysts preparation procedure using colloidal synthesis technique. For the sake of better comparison, Ni/(Ni + Mo + W) molar ratio for all the investigated catalysts (bimetallic and trimetallic) was kept the same (~0.28 ± 0.03). For the hydrodesulfurization of dibenzothiophene (DBT), because of improved synergistic effect, trimetallic NiMoW/γ-Al2O3 showed ~ 36% higher conversion in comparison to NiMo/ γ-Al2O3 and ~ 21% higher DBT conversion in comparison to NiW/ γ-Al2O3 catalyst. The catalytic activity of synthesized nanocatalysts was compared with catalyst prepared using well established metal impregnation method. Improved catalytic activity in case of synthesized NiMoW nanoclusters is attributed to the controlled partial substitution of Mo by W during the colloidal synthesis which enhances the synergistic effect.