Efficient Ru-based scrap waste automotive converter catalysts for the continuous-flow selective hydrogenation of cinnamaldehyde

Abstract

The selective, efficient and sustainable continuous flow hydrogenation of a α,β-unsaturated aldehyde, i.e. cinnamaldehyde, to the corresponding unsaturated alcohol, i.e. cinnamyl alcohol, using a novel catalyst based on Ru-containing scrap waste automotive converters is reported. The catalyst was prepared by recycling and upgrading waste ceramic-cores of scrap automotive catalytic converters as supporting materials. Ruthenium was incorporated into the ceramic structures using a simple, fast and solventless mechanochemically assisted procedure followed by a chemical reduction step. Different catalysts were prepared with varying Ru contents. The materials were characterized by XRD, N₂ physisorption, XPS, TEM, HRTEM and SEM/mapping analyses. Compared to Ru supported over most studied silica and alumina supports, the new system displayed an outstanding catalytic performance under continuous-flow conditions in terms of conversion and selectivity and a remarkable stability with time-on-stream, demonstrating a synergistic action between Ru and the waste catalytic converter support. A Ru loading of 10 wt% provided the optimum results, including a cinnamaldehyde conversion of up to 95% with a selectivity to cinnamyl alcohol of 80%.