Influence of W on the reduction behaviour and Brønsted acidity of Ni/TiO2 catalyst in the hydrogenation of levulinic acid to valeric acid: Pyridine adsorbed DRIFTS study

Abstract

Effect of W on 20wt%Ni/TiO2 catalyst is examined in the hydrogenation of levulinic acid (LA) to valeric acid at ambient H2 pressure. The interaction between W and Ni had a significant influence on the hydrogenation activity and product selectivity. The H2-TPR (temperature programmed reduction) results emphasized a shift in Tmax to very high temperatures due to W species which are in close proximity to Ni particles. The N2O decomposition measurements showed a decrease in N2O uptake with the increase in ‘W’ loadings due to a high ratio of Ni2+/Ni0 species at higher tungsten content. X-ray photoelectron spectra (XPS) demonstrated a shift in binding energy to higher owing to a strong interaction between W and Ni particles by the presence of ionic Ni at the near surface region. The ionic Ni species seems to be involved in the conversion of γ-valerolactone (GVL) to valeric acid (VA). Pyridine adsorbed infrared (IR) spectra revealed an enormous increase in surface Brønsted acidity originated from tungsten interacted Ni/TiO2 are the sites responsible for ring opening of GVL to form VA.