Originating from the desire to improve sustainability, producing fuels and chemicals from the conversion of biomass and waste plastic has become an important research topic in the twenty-first century. Although biomass is natural and plastic synthetic, the chemical nature of the two are not as distinct as they first appear. They share substantial structural similarities in terms of their polymeric nature and the types of bonds linking their monomeric units, resulting in close relationships between the two materials and their conversions. Previously, their transformations were mostly studied and reviewed separately in the literature. Here, we summarize the catalytic conversion of biomass and waste plastics, with a focus on bond activation chemistry and catalyst design. By tracking the historical and more recent developments, it becomes clear that biomass and plastic have not only evolved their unique conversion pathways but have also started to cross paths with each other, with each influencing the landscape of the other. As a result, this Review on the catalytic conversion of biomass and waste plastic in a unified angle offers improved insights into existing technologies, and more importantly, may enable new opportunities for future advances.

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Ketonization of fatty acids into fatty ketones is a potential route for producing high-value chemicals including bioderived lube base oil. In the present work, the catalytic selectivity and deactivation during the ketonization of C18 fatty acids having different unsaturation degrees over a TiO2 catalyst were rigorously investigated. The results demonstrated that the yield of fatty ketone gradually decreased with increasing unsaturation degree, while byproducts such as methyl ketones and olefins were produced owing to McLafferty rearrangement. It was verified that carboxylic acids longer than C5 can be decomposed via this pathway, the rate of which increased with the carbon chain length. In the ketonization of unsaturated fatty acids, the McLafferty rearrangement and cracking produced conjugated polyunsaturated olefins (e.g., dienes), which could be readily decomposed to coke. The results implied that the ketonization of natural fatty acids requires the presaturation of CC bonds for increasing the fatty ketone yield and inhibiting catalyst deactivation. Indeed, the ketonization of a natural fatty acid mixture obtained by palm oil hydrolysis exhibited diminished fatty ketone selectivity and rapid catalyst deactivation, owing to the presence of unsaturated fatty acids. In contrast, the ketonization of a saturated fatty acid mixture obtained by hydrogenative hydrolysis exhibited a high fatty ketone yield (∼90%) and negligible deactivation.