Influence of CeO2 supports prepared with different precipitants over Ru/CeO2 catalysts for ammonia synthesis

Three CeO 2 supports with different concentration of surface oxygen vacancies were prepared by using C 12 H 29 NO (TPAOH), C 2 H 8 N 2 (EDA) and NaOH as precipitant under hydrothermal conditions, respectively. Catalytic experiments showed that the Ru/CeO 2 -TPAOH catalyst has superior catalytic activity (22000 μmol g −1  h −1 ) than Ru/CeO 2 -EDA (19000 μmol g −1  h −1 ) and Ru/CeO 2 –NaOH (16500 μmol g −1  h −1 ) at 450 °C, 3 MPa. In addition, the introduction of Cs and Ba promoters improve the catalytic activity of the Ru/CeO 2 -TPAOH. However, the introduction of K promoter inhibits the catalytic activity of the Ru/CeO 2 -TPAOH. The 4% Cs promoter can effectively increase the catalytic activity of the Ru/CeO 2 -TPAOH (32000 μmol g −1  h −1 ). BET and TEM indicated that 5.5 nm average pore size of CeO 2 -TPAOH support contributes to the dispersion of active metal Ru. XPS and CO 2 -TPD proved that the Ru/CeO 2 -TPAOH catalyst has higher Ce 3+ concentration, more oxygen vacancies, and higher basic site density, which are important factors for improving ammonia synthesis activity.