Enhancement of ammonia synthesis activity on La2O3-supported Ru catalyst by addition of ceria

Abstract

The addition of Ce species in La2O3 can enhance the number of defect sites and generate the Ce1-xLaxO2-δ solid solution, thereby increasing the amount of the exposed ruthenium species and proportion of metallic ruthenium species. The presence of Ce species in Ru/La2O3 promotes the desorption of hydrogen, and hydrogen species prefers to desorb in the H2 molecule formation pathway. On the other hand, the difference in the Ce addition method strongly affects the exchange between the adsorbed hydrogen species on Ru catalyst with the gaseous hydrogen species. Owing to improvement of the proportion of oxygen vacancy, Ru0 and number of the exposure of ruthenium species, H2 species adsorbed on Ru/LaCe–C prepared by coprecipitation method preferentially desorbs in the formation of H2 pathway, and a large proportion of the adsorbed H species would exchange with the hydrogen species from the gaseous phase, which leads to improvement of ammonia synthesis rate by 75% in comparison with Ru/La2O3 catalyst.