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.

[Display omitted] • Valeric acid produced from levulinic acid in a single-step using formic acid as H 2 source. • Weak Lewis and strong Brønsted basic sites on Ni-La/TiO 2 surface was responsible for the high selectivity of valeric acid. • 99% selectivity of valeric acid was achieved using aqueous γ-valerolactone. • Surface metallic Ni in conjunction with surface acid-base sites were identified by N 2 O titration and in situ IR study. 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/TiO 2 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/TiO 2 surface was the reason for higher VA selectivity. The physicochemical characteristics of the modified Ni-M/TiO 2 (M = La, Ce, Pr and Nd) catalysts deduced from H 2 -TPR, N 2 O titration, TPD of NH 3 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. [ABSTRACT FROM AUTHOR]