Study on the Effect and Mechanism of Support and Deposition-Precipitation Method on Ru-Based Catalysts for Ammonia Decomposition

Herein, the effects of support and the deposition-precipitation method on the Ru-based catalysts for NH3 decomposition were studied. The results of the performance test, characterization, and DFT simulation show that the activity order of the catalysts with different supports is 5% Ru/MgO > 5% Ru/Al2O3 > 5% Ru/Pr2O3 > 5% Ru/La2O3. Ru/MgO exhibits the best ammonia decomposition performance (T80 ≈ 480 °C), because its suitable pore structure is conducive to ammonia adsorption, and abundant strong alkaline sites produce a strong metal–support interaction. The ammonia decomposition performance of 5% Ru/MgO (DP) prepared by the deposition-precipitation method is much higher than that of 5% Ru/MgO (IM) prepared by the impregnation method (T80 decreases from 480 to 440 °C). On Ru/MgO (DP), the distribution of Ru particles is more uniform and the particle size is relatively consistent, and the Ru/MgO (DP) has more basic sites and a more reasonable ratio of lattice oxygen to defect oxygen. Calculated by DFT, the energy barrier of the first dehydrogenation of NH3 and the combined desorption of N is 1.31 and 1.51 eV, respectively, and the latter is the rate-determining step of the ammonia decomposition reaction in Ru/MgO.