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

Abstract

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 (OIII 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 Ga2O2.952, Ga2O2.895, and Ga2O2.880, 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.