Titanium Dioxide Supported Ru Nanoparticles as Efficient Catalysts for Microwave-Assisted Sustainable Organic Transformations

Microwave-assisted organic transformation is currently gaining prominence in the field of benign organic synthesis. In this work, we reported Ru nanoparticles (NPs) (<5 nm) supported on titanium dioxide (TiO2) using the facile and fast molten-salt method and employed for reductive N-alkylation reactions, nitroarenes to amines and levulinic acid (LA) to levulinate ester under microwave irradiation (MWI). Reductive N-alkylation of nitrobenzene and furfural to the respective secondary amines via catalytic transfer hydrogenation with conventional heating (CH) involves longer reaction times, lower selectivity, and low yields. Moreover, the catalytic applications of Ru/TiO2 were explored for the reductive amination of nitrobenzene and furfural with excellent conversion (>99%) and selectivity (85%) toward N-(furan-2-ylmethyl) aniline. The Ru/TiO2 is used as a model to catalyze the conversion (>99%) of nitrobenzene in both the reaction, i.e., nitrobenzene reduction and one-pot reductive amination, along with LA esterification reaction via MWI. To study the efficacy of MWI for nitrobenzene conversion, MWI and CH were compared. MWI is proven to accelerate reaction times and improve nitrobenzene conversion efficiencies when compared to CH by examining the effects of conversion and reaction duration. A remarkable synergistic effect has been revealed between small Ru NPs and TiO2 NPs that leads to selective catalytic transformation of organic compounds to value-added products. As per the study’s findings, MW is a potentially effective method for improving the conversion of nitrobenzene, with Ru/TiO2 emerging as the most active catalyst compared to as-synthesized Cu/TiO2, and Ni/TiO2.