NbO-Based Catalysts for the Activation of C-O and C-C Bonds in the Valorization of Waste Carbon Resources.

Escalating energy demand, the depletion of fossil fuels, and abnormal climate change are recognized as the key challenges in the 21st century. The valorization of biomass and plastic, representing the most abundant natural and man-made polymers, respectively, as alternatives to fossil fuel is one of the promising solutions to creating a carbon-neutral, waste-free society. Catalysis is an essential tool for manipulating energy transformations via bond-breaking and bond-forming principles. To producing chemicals and fuels via biomass valorization and plastic upcycling, the cleavage of C-O and C-C bonds is the major catalytic route, given that the two are mainly constructed by various interunit C-O and C-C linkages. In this work, a consensus concerning the catalytic mechanism is reached: the activities for the cleavage of C-O and C-C bonds highly depend on the catalyst ability to activate the C-O and C-C bonds. Among the catalysts reported, NbO-based catalysts show a unique, superstrong ability to activate C-O and C-C bonds. While research on biomass valorization over NbO-based catalysts maintains its momentum, plastic upcycling driven by an efficient NbO-based catalyst capable of activating C-O and C-C bonds is quickly catching up. Therefore, deepening the understanding of NbO-based catalysts for the activation of C-O and C-C bonds is of importance to further drive biomass valorization and plastic upcycling, even in many other related areas. Herein, we present progress on the activation of C-O and C-C bonds in waste carbon resources, with an emphasis on our own work in using NbO-based catalysts. First, we introduce NbO-based catalysts for the activation of C-O and C-C bonds in biomass with a special focus on explaining how NbO-based catalysts activate C-O and C-C bonds and why NbO-based catalysts can activate C-O and C-C bonds so efficiently. Then, unified descriptors to embody the abilities to extract O from oxygenated compounds and an adsorbed benzene ring, namely "oxygen affinity" and "benzene ring affinity", were defined to standardize C-O and C-C activation chemistry. Furthermore, we highlight the emerging opportunities of NbO-based catalysts for plastic upcycling by learning the wisdom accumulated from the activation of C-O and C-C bonds in biomass. Finally, our own insights into future recommendations in this promising field are provided.