Highly Effective Ru/BaCeO3 Catalysts on Supports with Strong Basic Sites for Ammonia Synthesis.

Abstract

BaCeO3 -a and BaCeO3 -b, with strong basic sites, were synthesized by using a co-precipitation method at different calcination temperatures, and used as supports to evaluate their performance in ammonia synthesis. The ammonia synthesis rate with the 1.25 % Ru/BaCeO3 -a catalyst is 24 mmol g-1 h-1 , which is higher than that of 1.25 % Ru/BaCeO3 -b catalyst (18 mmol g-1 h-1 ) at 3 MPa and 450 °C. Moreover, the performance of the 4 % Cs-1.25 % Ru/BaCeO3 -a catalyst was further improved to 28 mmol g-1 h-1 , and no sign of deactivation was observed after a reaction time of 120 h. The XPS and H2 temperature-programmed reduction analyses indicated that the Ru/BaCeO3 -a catalyst has more oxygen vacancies than the Ru/BaCeO3 -b catalyst. In addition, the average Ru particle size of the Ru/BaCeO3 -a catalyst is closer to 2 nm than the Ru/BaCeO3 -b catalyst, which promotes the generation of B5 -type sites (the active site for N2 dissociation). The CO2 temperature-programmed desorption analysis indicates that BaCeO3 -a has a high basic density, which is beneficial for electron transfer to Ru and further facilitates the dissociation of N≡N bonds.