Synergistic enhancement of catalytic hydrodeoxygenation performance by oxygen vacancies and frustrated Lewis pairs.

[Display omitted] • Ni/N 0.8 -CeO 2 was prepared through the capping effect of ionic liquids for the first time. • Ni/N 0.8 -CeO 2 exhibits the highest yields of saturated cycloalkanes using precious metal-free catalysts. • Ni/N 0.8 -CeO 2 excellent performance is due to the synergistic catalysis of OVs and adjacent FLPs of N/Ce3+. • FLPs of N/Ce3+ and Ni nanoparticles produce active hydrogen via a relay catalysis. • FLPs-generated hydrogen and OVs-specific oxygen recognition synergistically enhance catalytic efficiency. The catalytic hydrodeoxygenation (CHDO) of lignin into saturated cycloalkanes not only enhances the efficient utilization of lignin but also reduces reliance on high-density liquid fuels (HDLFs), given the importance of saturated cycloalkanes as key constituents of HDLFs. The main challenge in lignin CHDO towards HDLFs is efficiently removing oxygen-atom while maintaining high selectivity for the desired saturated cycloalkanes. Herein, we report for the first time the fabrication of a Ni/N 0.8- CeO 2 -500 composite with abundant oxygen vacancies (OVs) and adjacent frustrated Lewis pairs (FLPs), achieved through the capping effect of ionic liquids. The FLPs of N/Ce3+ within Ni/N 0.8 -CeO 2 -500, mediated by OVs, not only enhance the dispersion of Ni species but also effectively facilitate the conversion of H 2 into active hydrogen (H*) through relay catalysis involving the Ni species. This integration, combining the oxygen atom-specific recognition of OVs with the adjacent FLPs of N/Ce3+ for the tandem generation of H*, significantly promotes the adsorption/cleavage of C ar/alk −O−C alk bonds, oxygen-atom removal, and hydrogenation of aromatic rings, ultimately catalyzing the one-step production of saturated cycloalkanes. The synergistic catalytic interplay results in a remarkable yield of saturated cycloalkanes (up to 88.2 wt%) during the CHDO of Kraft lignin, representing the highest reported value under similar conditions to date. A combination of diverse characterizations, experimental analyses, and kinetic studies collectively reinforces the notion that in-situ N-doping of CeO 2 increases the electron cloud density around Ce species, forming N-Ceδ+ entities that, at high temperatures, create OVs and adjacent FLPs of N-Ce3+, collectively enhancing lignin CHDO to yield saturated cycloalkanes. [ABSTRACT FROM AUTHOR]