Tuning ligand-vacancies in Pd-UiO-66 to boost biofuel production from 5-hydroxymethylfurfural hydrodeoxygenation

The hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) to biofuel 2,5-dimethylfuran (DMF) serves as a vital reaction in biomass refineries. Herein, Pd-UiO-66 catalysts with controlled contents of ligand-vacancies were developed for the HMF-to-DMF conversion. Strikingly, a volcano-like relationship between defect level and HDO activity was obtained. The DMF yield was promoted ∼3 times, reaching 92.2 % at 160 °C and 15 bar H, which refers to a high-level turnover frequency value of 42.66 h among the reported candidates. The Pd-UiO-66 catalysts also afforded >80 % yield for the HDO of 5-methyl furfural, furfural, and vanillin. Besides, high HDO activity could be retained in five recycles. Manipulating the contents of ligand-vacancies was confirmed to create more Pd species and Bronsted acid sites, leading to remarkable performance. This work provides significant inspiration for tuning structural defects in MOFs to realize the efficient HDO of platform molecules in biomass valorization.