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-Ga 2 O 3 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 Ga 2 O 3 monoliths after the reduction treatment. The number of oxygen vacancies in the reduced monoliths gives 2.32 × 10 13 , 2.87 × 10 13 , and 3.45 × 10 13 mg −1 for the Ga 2 O 2.952 , Ga 2 O 2.895 , and Ga 2 O 2.880 , respectively. We therefore demonstrate the exceptionally high C 2 H 4 selectivity of ~100% at the C 2 H 6 conversion of ~37% for nonoxidative dehydrogenation of C 2 H 6 to C 2 H 4 . We further demonstrate the excellent durability even at 620 °C for 240 h of continuous operation.