Cross-metathesis of biomass to olefins: Molecular catalysis bridging the gap between fossil and bio-energy

Terminal olefins are important building blocks for the industry of biofuels, oligomers, and lubricants production. The industrial processes for production of olefins involving oligomerization of ethylene or cracking of petrochemical waxes have several flaws including low yield and high cost in product separation. Cross-metathesis of bio-derived unsaturated fatty esters and olefins with ethylene (ethenolysis), allows the conversion of sustainable waste biomass to various renewable olefins with much safer, less toxic, sustainable, and zero-CO2 emission processes. To our best knowledge, however, a comprehensive summary of key advances in this field (since 2017) is yet to be available, particularly on molecular features of homogeneous and heterogeneous catalysts. This paper presents a critical review on molecular structures of metal complex and oxide catalysts for ethenolysis of olefins and oleochemicals. The influence of cationic centers, coordination conditions, nature of ligands, operating conditions on catalyst performances will be systematically discussed along with relevant reaction mechanism. The key challenges for rational design of coordinated cationic hybrids have been summarized, which will provide insights to technological advancement of large-scale production of oleochemical-derived olefins.