Insights into the enhanced hydrogen adsorption on M/LaO (M = Ni, Co, Fe).

Lanthanum oxide (LaO) possesses superior reactivity during catalytic hydrogenation, but the intrinsic activity of LaO toward H adsorption and activation remains unclear. In the present work, we fundamentally investigated hydrogen interaction with Ni-modified LaO. Hydrogen temperature programmed desorption (H-TPD) on Ni/LaO shows enhanced hydrogen adsorption with a new hydrogen desorption peak at a higher temperature position compared to that on the metallic Ni surfaces. By systematically exploring the desorption experiments, the enhanced H adsorption on Ni/LaO is due to the oxygen vacancies formed at the metal-oxide interfaces. Hydrogen atoms transfer from Ni surfaces to the oxygen vacancies to form lanthanum oxyhydride species (H-La-O) at the metal-oxide interfaces. The adsorbed hydrogen at the metal-oxide interfaces of Ni/LaO results in improved catalytic reactivity in CO methanation. Furthermore, the enhanced hydrogen adsorption on the interfacial oxygen vacancies is ubiquitous for LaO-supported Fe, Co, and Ni nanoparticles. Benefiting from the modification effect of the supported transition metal nanoparticles, the surface oxyhydride species can be formed on LaO surfaces, which resembles the recently reported oxyhydride observed on the reducible CeO surfaces with abundant surface oxygen vacancies. These findings strengthen our understanding of the surface chemistry of LaO and shed new light on the design of highly efficient LaO-based catalysts with metal-oxide interfaces.