Nanohydrotalcite Supported Ruthenium Nanoparticles: Highly Efficient Heterogeneous Catalyst for the Oxidative Valorization of Lignin Model Compounds

Abstract

The catalytic transformation of lignocellulosic biomass derived chemicals into value-added chemicals under mild conditions remains a challenge in the fields of synthetic chemistry and catalysis. Herein, we describe a new heterogeneous catalyst system that efficiently works in the oxidative valorization of lignin model compounds. This new heterogeneous catalyst system comprised of nano-sized hydrotalcite (n-HT; Mg6Al2 (CO3)(OH)(16)) supported ruthenium(0) nanoparticles (Ru/ n-HT) was prepared by ion-exchange of [Ru(OH2)Cl-5](2-) anions with the extraframework CO32- anions of n-HT followed by their borohydride reduction (NaBH4) in water at room temperature. The characterization of Ru/n-HT was done by the combination of various spectroscopic and the sum of their results revealed that the formation of well-dispersed ruthenium(0) nanoparticles with a mean diameter of 3.2 +/- 0.9 nm on the surface of n-HT structure. The catalytic performance of Ru/n-HT in terms of activity, selectivity and stability was tested in the aerobic oxidation of cinnamyl, veratryl and vanillyl alcohols, which are important lignin model compounds used to mimic the propyl side chain, the phenolic and non-phenolic, respectively functional groups of lignin. We found that Ru/ n-HT nanocatalyst displays remarkable activity at high selectivity and almost complete conversion in these catalytic transformations under mild reaction conditions (at 373 K under 3 bar initial O-2 pressure).