Maximizing Active Site Concentrations at Ni-Substituted WS₂Edges for Hydrogenation of Aromatic Molecules

Abstract

High concentrations of Ni in bimetallic sulfide catalysts lead to the formation of segregated Ni sulfides (NiS x ), which are rather inactive alone as large crystallites and even impede the accessibility of active sites at the sulfide slab edges that catalyze a multitude of hydrogenation reactions and H 2 and CO 2 activation processes. Treatment of Ni-WS 2 /γ-Al 2 O 3 catalysts in aqueous acids, particularly concentrated HCl, results in a significant reduction of NiS x and ≤5-fold enhancement of the phenanthrene hydrogenation rate. Using infrared (IR) spectroscopy of probe molecules, we show that the acid-treated catalysts have a high concentration of accessible metal edge sites, a high degree of Ni substitution, and consequently a high sulfhydryl (SH) concentration at the slab edges in the presence of H 2 . The site-specific "turnover frequency" (based on SH concentrations determined by IR measurements) is identical for all parent and acid-treated sulfide catalysts studied, showing that excess NiS x does not influence electronic properties.

Nanomaterials in photocatalysed organic transformations: development, prospects and challenges

“…Quite interestingly, the hydrogenation of aliphatic and aromatic systems could be achieved with these materials as well. For instance, cyclohexene could be hydrogenated with MoS 2 nanoflowers 61 while phenanthrene required a Ni-WS 2 /γ-Al 2 O 3 composite 62 for the same.…”