Oxidized Biochar as a Simple, Renewable Catalyst for the Production of Cyclic Carbonates from Carbon Dioxide and Epoxides

Abstract

Hard‐ and softwood (birch and pine respectively) residues from the forestry, and pulp and paper industry, e.g. sawdust, branches, were used to prepare biochar, which was then oxidized using nitric acid to produce catalytic carboxylic acid functionalized biochar. This oxidized biochar, ox‐bc, in the presence of a co‐catalyst, showed excellent catalytic activity towards the cycloaddition reaction between CO2 and epoxides using mild conditions (CO2 pressure, 10 bar). No differences in catalytic activity were seen between the two types of oxidized biochar despite the hardwood ox‐bc having a significantly higher surface area. The catalysts function through activation of the epoxide reagent via hydrogen‐bonding with carboxylic acid groups on the surface. The number of surface acid groups was reduced by reaction with 3‐aminopropyltriethoxysilane and the resulting material was inactive in the reactions studied. The ox‐bc catalysts are sustainable and renewable alternatives for currently used heterogeneous systems and also exhibit good recyclability (over five runs).