Decoration of Ru nanoparticles on γ-alumina with sub-nanometer ceria species for efficient catalytic ammonia synthesis

Abstract

Utilization of promoters to improve the catalytic performance of supported metal catalysts is an important strategy for the design of efficient catalysts. However, it is difficult to detect the relationship between the promoters and the structure of main catalysts. Herein, we firstly develop an efficient Ru-based ammonia synthesis catalyst by decorating Ru nanoparticles (NPs) on γ-alumina with sub-nanometer ceria (CeO₂) species (Ce–Ru/Al₂O₃). In comparison with neat Ru/Al₂O₃, Ce–Ru/Al₂O₃ exhibits up to 10-fold activity enhancement at 400 °C and 1.0 MPa. Our characterization results show that such an activity increment is relevant to the function of the sub-nanometer CeO₂ species on the Ru NPs. The sub-nanometer CeO₂ species will aggregate around the Ru nanoparticles, leading to a clear electron transfer from sub-nanometer CeO₂ species to Ru nanoparticles. At the same time, the introduction of CeO₂ species can not only weaken the hydrogen poisoning effect on the Ru nanoparticles but also facilitate nitrogen adsorption and hydrogenation of dissociated N* atoms according to the kinetic test results. This work highlights the important role of highly dispersed rare earth oxide promoter species in modulating the structure and catalytic performance of supported Ru NPs for ammonia synthesis.