Insight into the Role and Evidence of Oxygen Vacancies in Porous Single-Crystalline Oxide to Enhance Catalytic Activity and Durability

Introducing and stabilizing oxygen vacancies in oxide catalysts is considered to be a promising strategy for improving catalytic activity and durability. Herein, we quantitatively create oxygen vacancies in the lattice of porous single-crystalline β-Ga₂O₃ monoliths by reduction treatments and stabilize them through the long-range ordering of crystal lattice to enhance catalytic activity and durability. The combination analysis of time-of-flight neutron powder diffraction and extended x-ray absorption fine structure discloses that the preferential generation of oxygen vacancy tends to occur at the site of tetrahedral coordination oxygen ions (O_III sites), which contributes to the formation of unsaturated Ga-O coordination in the monoclinic phase. The oxygen vacancies are randomly distributed in lattice even though some of them are present in the form of domain defect in the PSC Ga₂O₃ monoliths after the reduction treatment. The number of oxygen vacancies in the reduced monoliths gives 2.32 × 10¹³, 2.87 × 10¹³, and 3.45 × 10¹³ mg^-1 for the Ga₂O_2.952, Ga₂O_2.895, and Ga₂O_2.880, respectively. We therefore demonstrate the exceptionally high C₂H₄ selectivity of ~100% at the C₂H₆ conversion of ~37% for nonoxidative dehydrogenation of C₂H₆ to C₂H₄. We further demonstrate the excellent durability even at 620 °C for 240 h of continuous operation.