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A series of BaCeO3 modified with different rare earth elements(La,Y,Pr)were synthesized by co-precipitation and calcination and the effect of rare earth elements for catalytic ammonia synthesis un-der mild conditions was studied.The ammonia synthesis performance tests show that 2.5％Ru/BaCe0.9La0.1O3-δ catalyst(All the percentages of Ru in this article are in mass fraction)exhibits the highest ammonia synthesis rate(34 mmol/(g·h))at 3 MPa,450 ℃,and no sign of deactivation after 100 h of reaction.H2-TPR and XPS analyses indicate that the introduction of La increases the amount of oxygen vacancies of the catalyst,which is beneficial to increasing the electron density of Ru surface.HRTEM analysis shows that the Ru particle size is reduced greatly after La is introduced,which facilitates the catalyst generating more B5-type sites(active sites of Ru species for N≡N dissociation).CO2-TPD analysis indicates that BaCe0.9La0.1O3-δ has stronger basicity,which promotes electrons transfer from support to Ru.This work provides an effective method for design and synthesis of Ru-based multi-element com-posite perovskite oxide catalysts.