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

Abstract

Three CeO2 supports with different concentration of surface oxygen vacancies were prepared by using C12H29NO (TPAOH), C2H8N2 (EDA) and NaOH as precipitant under hydrothermal conditions, respectively. Catalytic experiments showed that the Ru/CeO2-TPAOH catalyst has superior catalytic activity (22000 μmol g−1 h−1) than Ru/CeO2-EDA (19000 μmol g−1 h−1) and Ru/CeO2–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/CeO2-TPAOH. However, the introduction of K promoter inhibits the catalytic activity of the Ru/CeO2-TPAOH. The 4% Cs promoter can effectively increase the catalytic activity of the Ru/CeO2-TPAOH (32000 μmol g−1 h−1). BET and TEM indicated that 5.5 nm average pore size of CeO2-TPAOH support contributes to the dispersion of active metal Ru. XPS and CO2-TPD proved that the Ru/CeO2-TPAOH catalyst has higher Ce3+ concentration, more oxygen vacancies, and higher basic site density, which are important factors for improving ammonia synthesis activity.