Valorisation of lignocellulose and low concentration CO 2 using a fractionation-photocatalysis-electrolysis process

The simultaneous upcycling of all components in lignocellulosic biomass and the greenhouse gas CO presents an attractive opportunity to synthesise sustainable and valuable chemicals. However, this approach is challenging to realise due to the difficulty of implementing a solution process to convert a robust and complex solid (lignocellulose) together with a barely soluble and stable gas (CO ). Herein, we present the complete oxidative valorisation of lignocellulose coupled to the reduction of low concentration CO through a three-stage fractionation-photocatalysis-electrolysis process. Lignocellulose from white birch wood was first pre-treated using an acidic solution to generate predominantly cellulosic- and lignin-based fractions. The solid cellulosic-based fraction was solubilised using cellulase (a cellulose depolymerising enzyme), followed by photocatalytic oxidation to formate with concomitant reduction of CO to syngas (a gas mixture of CO and H ) using a phosphonate-containing cobalt(ii) bis(terpyridine) catalyst immobilised onto TiO nanoparticles. Photocatalysis generated 27.9 ± 2.0 μmol g (TON = 2.8 ± 0.2; 16% CO selectivity) and 147.7 ± 12.0 μmol g after 24 h solar light irradiation under 20 vol% CO in N . The soluble lignin-based fraction was oxidised in an electrolyser to the value-added chemicals vanillin (0.62 g kg ) and syringaldehyde (1.65 g kg ) at the anode, while diluted CO (20 vol%) was converted to CO (20.5 ± 0.2 μmol cm in 4 h) at a Co(ii) porphyrin catalyst modified cathode (TON = 707 ± 7; 78% CO selectivity) at an applied voltage of -3 V. We thus demonstrate the complete valorisation of solid and a gaseous waste stream in a liquid phase process by combining fractioning, photo- and electrocatalysis using molecular hybrid nanomaterials assembled from earth abundant elements.