Synergetic effect between Pd clusters and oxygen vacancies in hierarchical Nb2O5 for lignin-derived phenol hydrodeoxygenation into benzene

Lignin could be depolymerized into large amount of phenolic compounds via fast pyrolysis. The upgrade of phenolic compounds via hydrodeoxygenation (HDO) involves multiple reaction pathways. It is challenging to selectively remove the oxygen-containing groups while keeping the aromatic rings intact. In this work, hierarchical Nb2O5 (H–Nb2O5) microspheres with abundant oxygen vacancies were synthesized to anchor the Pd clusters, which is featured with strong metal-support interaction via the electron transfer between Pd species and Nb species. For phenol HDO reaction, the oxygen vacancies were prone to interact with the phenolic hydroxy groups, resulting in phenol molecule adsorbed in a “nonplanar” manner, greatly weakening the CAr-O bonds and averting the ring hydrogenation. Besides, the activated hydrogen atoms on Pd clusters could migrate to the vicinity of oxygen vacancies via spillover, promoting the cleavage of CAr-O bond to obtain benzene. Current work provides a deep insight into the synergetic catalytic mechanism of Pd/H–Nb2O5 catalyst for phenol HDO reaction, and also sheds light on the design and synthesis of high-efficient catalysts in other heterogeneous catalysis fields.