Evaluation of Kinetic Models for the Catalytic Hydrogenation of Levulinic Acid to γ-Valerolactone over Nickel Catalyst Supported by Titania

The search for alternative sources of, and substitutes for, chemicals derived from fossil-based feedstocks encourages studies of heterogeneous catalysts to increase the feasibility of sustainable production of biomass derivatives, such as gamma-valerolactone, among others. In this context, first, the performance of a titania-supported nickel catalyst (a non-noble catalyst) was evaluated in the reaction of hydrogenation of levulinic acid to gamma-valerolactone in water using molecular hydrogen. The methods used included the synthesis of titania via the solgel method and nickel deposition by deposition-precipitation via removal of the complexing agent. The nickel was activated in a flow of hydrogen; the temperature of reduction and the calcination step were investigated with experiments at reaction conditions to study the catalyst's stability. Then, after a statistical evaluation of several proposed kinetic models, the kinetics of the reaction was found to be best represented by a model obtained considering that the reaction over the surface was the determinant step, followed by the non-dissociative adsorption of hydrogen and the competitive adsorption among hydrogen, levulinic acid, and gamma-valerolactone. With that model, the activation energy of the levulinic acid to 4-hydroxypentanoic acid step was (47.0 +/- 1.2) kJ mol-1, since the determinant step was the hydrogenation reaction of the levulinic acid to 4-hydroxypentanoic acid. It was also concluded that the catalyst prepared was stable, active, and selective to gamma-valerolactone.