In(2)O(3) Nanocrystals for CO(2) Fixation: Atomic-Level Insight into the Role of Grain Boundaries

N-functionalization of amines with CO(2) and H(2) is one of the most important processes to make use of CO(2). Although noble metal-based catalysts with remarkable performance have been widely used in this process, developing efficient non-noble-metal-based catalysts remains a grand challenge. Herein, we report In(2)O(3) nanocrystals with high density of grain boundaries (HGB-In(2)O(3)), which show excellent activity toward methylation of amines. Impressively, HGB-In(2)O(3) achieved the optimal yield of 82.7% for N,N-dimethylaniline with a mass activity of 21.2 mmol·g(−1)h(−1) in methylation of N-methylaniline, comparable to noble-metal-based catalysts. As a bonus, HGB-In(2)O(3) held noticeable stability, remarkable selectivity, and comprehensive applicability. Further mechanistic studies revealed that the presence of high density of grain boundaries not only facilitated the adsorption and activation of CO(2) to generate CH(3)OH as the intermediate but also enhanced the activation of N-H bond in amines, contributing to the attractive activity of HGB-In(2)O(3) toward methylation of amines.