Influence of biochar composition and source material on catalytic performance : the carboxylation of glycerol with CO2 as a case study

The impact of the chemical and physical composition of biochar catalysts is demonstrated in the carboxylation of glycerol with carbon dioxide for the first time, using acetonitrile as a dehydrating agent. Biochars are an important emerging class of catalytic material that can readily be produced from low-value biomass residues; however, the impact of feedstock choice is often overlooked. The ash content of biochar from three different feedstocks is shown to be catalytically active for the production of glycerol carbonate and triacetin, whilst low-ash catalysts such as soft wood biochar and commercial activated charcoal are inactive. Following treatment with hydrochloric acid, yields of glycerol carbonate over ash were reduced by over 94%, and triacetin was no longer produced. This has been attributed to the loss of potassium content. Carbon content was shown to be catalytically active for the synthesis of diacetin, and graphitic carbon may be beneficial. Through the development of structure–performance relationships, biomass feedstocks with the most suitable properties can therefore be selected to produce biochars for specific catalytic applications. This would expand the range of reactions which can be effectively catalysed by these materials and enhance the development of a more circular and sustainable chemicals industry.