Ni/SiO2 catalysts prepared with ethylenediamine nickel precursors: Influence of the pretreatment on the catalytic properties in glucose hydrogenation

Abstract

Nickel catalysts prepared with different metal loadings (5, 10, and 20 wt% Ni) by impregnation with nickel ethylenediamine complexes revealed small nickel particles (mean diameter: 2–3 nm) after reduction, even for high metal loadings (20 wt%). When used in the hydrogenation of glucose, these catalysts show almost no nickel leaching compared to a commercial Ni/SiO2 catalyst (prepared by precipitation, 67 wt% Ni), but they are slightly less active (TOF: 2 to 10 × 10−3 s−1) than a commercial nickel/silica catalyst (TOF: 14 × 10−3 s−1) and revealed lower yields to sorbitol (3–42% compared to 60%). The catalytic results depend on the pretreatment conditions performed. When the catalysts are calcined before reduction, higher conversion (19–45%) and selectivity to sorbitol (81–92%) are obtained than when they are directly reduced without calcination pretreatment (conversion: 10–16% and selectivity to sorbitol: 21–59%) after 5 h of reaction time, respectively. The difference was ascribed to the fact that complete decomposition of the nickel ethylenediamine precursor was achieved only when calcination pretreatment was performed. Indeed, when the catalysts were directly reduced, X-ray photoelectron spectroscopy (XPS) revealed a nitrogen-compound probably responsible for lower conversion and higher selectivities to fructose and mannose, indicating Lobry de Bruyn-Alberda van Ekenstein rearrangement. However, no nickel sintering was observed in contrast to the catalyst calcined before reduction.