Pd supported on mixed metal oxide as an efficient catalyst for the reductive amination of bio-derived acetol to 2-methylpiperazine

Abstract

An efficient process for synthesizing a high added-value N-heterocycle (2-methylpiperazine, 2-MP) via reductive amination of hydroxyacetone or acetol (product of the selective dehydration of glycerol) with ethylenediamine by using Pd supported catalysts under mild reaction conditions is here presented. Catalysts based on Pd nanoparticles supported on metallic oxides and mixed oxides were prepared and characterized by ICP analysis, XRD, HR-TEM, and NH₃-TPD, among others. Catalytic activity comparisons of Pd-based materials (also including commercial references) were done and obtained results correlated with metal particle morphology (analyzed by CO-FTIR) and its ability to activate the CN bond. The best results were attained with Pd/TiO₂–Al₂O₃ and Pd/ZrO₂–Al₂O₃, the former yielding >80% of 2-MP. The Pd/TiO₂–Al₂O₃ catalyst successfully enables the activation of the imine group (CN), due to a larger number of unsaturated Pd sites in its nanoparticles, while keeping a suitable acidity to effectively and selectively carry out the reductive cyclo-amination reaction even with lower catalyst loadings. This research work offers a new and sustainable catalytic route for the synthesis of organo-nitrogen compounds taking advantage of renewable raw materials (i.e. acetol) as a carbon source and using efficient Pd supported catalysts.