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

Abstract

In the present work, NiW/Al2O3 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 WS2 increases with the increase of the thermal treatment temperature while the WS2 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 WS2 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.