Lignin refinery based on efficient thermo-photo-catalysis of Ru-RuO2/TiO2-Deep Eutectic Solvents

Abstract

A Lignin refinery with high-yields and high-selectivities towards aromatic monomers under mild conditions is challenging. A thermo-photo-catalysis system based on deep eutectic solvents (DESs) and Ru-RuO2/TiO2 is described here and exhibits excellent oxidation depolymerization performance towards both model lignin compounds and coconut shell lignin under mild conditions. When using the β-O-4 model substrate, a 99.45% conversion rate was achieved with a phenol yield of 99.34% at 80 ℃, 1MPa O2, 300W visible light irradiation, and the presence of Glycerol-Choline chloride (Gly-ChCl) DES for 2 hours. More importantly, the raw material of coconut shell gave a phenol yield of 27.5% (w/w) due to the high productivity of 87.65% for authentic lignin in tetramethylammonium hydroxide-imidazole (TMAH-Imidazole) DES at 100 ℃ for 3 hours. The Ru(100)-RuO2(110) interfaces serve as active sites for substrate adsorption and the cleavage of C-O bonds, while the TiO2 support enables efficient charge separation. During the catalytic process, light irradiation could adjust the electronic structure of the catalyst surface to provide adequate active sites, and thermal energy could facilitate the separation and transport of photo-generated electron-hole pairs. A “win-win” situation of low energy consumption and high aromatic yield of lignocellulosic biomass refinery was achieved in this Ru-RuO2/TiO2-DESs system.