Pd/ZrO₂-TiO₂ Catalyst for Reductive Amination of Furfural: Exploring Solvent and N-Substrate Effects

The valorization of furfural (FUR) through reductive amination is a sustainable alternative for producing secondary aromatic amines; however, this process holds relevant scientific challenges associated to reaction conditions, catalytic materials as well as on the understanding of reaction mechanisms. This study systematically investigates the effect of the solvent and N-substrates nature on the reductive amination of FUR using a bifunctional Pd/ZrO2-TiO2 catalyst. The catalyst presented an anatase TiO2 phase, high Pd dispersion (22%), and a predominance of weak Lewis's acid sites. The solvent screening demonstrated that methanol provided a balance of hydrogen-bonding ability and dielectric constant, which favor H₂ dissociation at metal sites and imine adsorption at acid sites, thus favoring N-furfurylaniline (FFA) selectivity. Among the tested substrates the 3-Fluoroaniline resulted in the highest yield and selectivity to secondary amine FFA (YFFA = 76%; SFFA = 82%), due to increased electrophilicity of the C=N group, while ortho substituents generated hysteric hindrance, limiting FFA formation. These findings could contribute to the rational design of catalysts and the selection of more suitable reaction systems for the reductive amination of FUR.