Breaking C─C Bonds and Preserving C─O Bonds in Aromatic Plastics and Lignin via a Reversing Bond Energy Cleavage Strategy

Abstract

In the conversion of aromatic plastics, the breaking of C─O bonds with lower dissociation energy is generally easier than that of C─C bonds with higher dissociation energy. The obtained products are hydrocarbons through this type of bond-breaking sequence, wasting important inherent O-containing groups of these feedstocks. Here, using Ru/Nb2O5 as a catalyst, a strategy of inhibiting C─O cleavage by site-specific methanol poisoning was developed to achieve the selective cleavage of C─C bonds in aromatic plastics to produce monocyclic phenolic compounds via a reversing bond energy cleavage strategy. It is found that lower-coordinated NbOx species are the adsorption–activation sites of C─O bonds, and methanol can dominantly occupy these sites, thus inhibiting the undesirable C─O bond cleavage. Moreover, methanol also covers most of Ru sites in a nonselective manner, further preventing the C─O cleavage because of its high sensitivity to H species. However, this poisoning effect is not serious enough to obviously reduce the activity for C─C bond cleavage, thus contributing to this reversing bond energy cleavage manner. Finally, we proposed a universal scheme for how to reach this cleavage manner in the future study. This work can boost the development of bond cleavage chemistry and expand the scope of end products from waste feedstocks.