Insights into the enhanced hydrogen adsorption on M/La₂O₃ (M = Ni, Co, Fe)

Lanthanum oxide (La₂O₃) possesses superior reactivity during catalytic hydrogenation, but the intrinsic activity of La₂O₃ toward H₂ adsorption and activation remains unclear. In the present work, we fundamentally investigated hydrogen interaction with Ni-modified La₂O₃. Hydrogen temperature programmed desorption (H₂-TPD) on Ni/La₂O₃ 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 H₂ adsorption on Ni/La₂O₃ 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/La₂O₃ results in improved catalytic reactivity in CO₂ methanation. Furthermore, the enhanced hydrogen adsorption on the interfacial oxygen vacancies is ubiquitous for La₂O₃-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 La₂O₃ surfaces, which resembles the recently reported oxyhydride observed on the reducible CeO₂ surfaces with abundant surface oxygen vacancies. These findings strengthen our understanding of the surface chemistry of La₂O₃ and shed new light on the design of highly efficient La₂O₃-based catalysts with metal-oxide interfaces.