Effect of thermal treatment on morphology and catalytic performance of NiW/Al2O3 catalysts prepared using citric acid as chelating agent.

In the present work, NiW/Al 2 O 3 catalyst was prepared with the use of citric acid and thermally treated at temperatures of 120, 220, 300 and 450 °C. It was shown that the thermal treatment at temperatures of 220–300 °C leads to decomposition of citrate ligands, 450 °C – to the almost complete removal of organic carbon. HRTEM of the sulfided catalysts showed that stacking number of WS 2 increases with the increase of the thermal treatment temperature while the WS 2 slab length has minimum at 220 °C. The results of XPS indicated that the sulfidation degree of tungsten and nickel decreases with the increase of the thermal treatment temperature. The catalyst thermally treated at 300 °C resulted to be most active in DBT HDS, quinoline HDN and naphthalene hydrogenation reactions. The higher activity of this catalyst in comparison with the samples thermally treated at 120 °C and 220 °C can be explained by an increased stacking degree of the sulfide WS 2 slabs while maintaining a small length of sulfide slabs and by a smaller carbon content that can impede access to the active sites. The calcination at 450 °C leads to low activity due to the low dispersion of the active component and a decrease in the degree of sulfidation of tungsten and nickel. [ABSTRACT FROM AUTHOR]