Improved promoter effect in NiWS catalysts through a molecular approach and an optimized Ni edge decoration

An efficient preparation method - based on the grafting and deposition of Ni and W molecular precursors onto partially dehydroxylated amorphous silica-alumina followed by a thermal treatment under H2S/H-2 - generates supported NiWS catalysts exhibiting enhanced activities in toluene hydrogenation, by comparison with conventional samples, prepared from metallic salts. A careful analysis of these materials by IR, XPS, TEM, HAADF-STEM, together with DFT calculations, reveals that the improved activity probably originates from the lower sulfidation temperature of W that improves distribution of Ni-W mixed sites at the edges of NiWS crystallites. This provides an optimal compromise between intrinsic activity and surface concentration of active sites. (C) 2016 Elsevier Inc. All rights reserved.