2D graphene derivatives as heterogeneous catalysts to produce biofuels via esterification and trans-esterification reactions

Abstract The shortage of fossil fuels and burgeoning global warming has increased the demand for clean energy making biodiesel a promising alternative to conventional fuels. Heterogeneous catalysis plays a vital role in the cost-effectiveness of the expensive conventional biodiesel synthesis via transesterification reactions between lipid feedstocks such as vegetable oil or long chain fatty acids and alcohols. 2D carbons, such as graphene derivatives, have been used as catalysts for the biodiesel production owing to their extraordinary physical, electronic and mechanical properties. However, irreversible agglomeration, restacking of sheets, low bulk density leading to low catalyst mass/reactor volume ratio, and poor dispersibility of the graphene-based catalysts in most organic solvents are major challenges, restricting their use as catalysts or heterogeneous catalysts support. The properties of 2D carbons can be improved by introducing appropriate functionalities and defects, doping by heteroatoms and grafting of nanoparticles for the selective conversion of non-conventional sources into biofuels. Herein, we review the recent developments in graphene derivatives for the catalytic esterification and transesterification reactions, through a broad discussion on the synthesis of heterogeneous graphene derivatives as catalysts and their application in biodiesel production.