Elucidation of surface active sites by formic acid adsorbed IR studies in the hydrogenation of levulinic acid to valeric acid over rare earth metal doped titania supported nickel catalysts

Abstract

Titania supported Ni catalyst modified by different lanthanides (La, Ce, Pr and Nd) were evaluated for the one-step conversion of levulinic acid (LA) to valeric acid (VA) using formic acid as a hydrogen source. Among these, the La modified Ni/TiO2 demonstrated better VA yields with an optimum LA to VA mole ratio of 1:3. Pyridine and/or formic acid adsorbed IR studies revealed that presence of weak Lewis and strong basic sites present on the Ni-La/TiO2 surface was the reason for higher VA selectivity. The physicochemical characteristics of the modified Ni-M/TiO2 (M = La, Ce, Pr and Nd) catalysts deduced from H2-TPR, N2O titration, TPD of NH3 and catalytic activity data emphasized a combination of metallic Ni with surface acid-base sites were responsible for the formation of VA in single step. Using aqueous γ-valerolactone, 99 % selectivity towards VA was achieved. A plausible reaction mechanism has been proposed based on the kinetic data obtained at moderate temperatures and ambient pressures.