Studies On Mechanism And Resistance Of Carbon-Methanation On Active Carbon Supported Ru-Based Ammonia Synthesis Catalyst

The catalytic synthesis of ammonia has been studied extensively in both aspects of the fundamental understanding and industrial application, which have a significant influence on the development of heterogeneous catalysis sciences and technology. The promoted ruthenium-based catalysts are expected to be the second-generation catalysts for ammonia synthesis behind the fused-iron catalyst. Therefore, studies on the Ru-based catalysts has been attracted much attention. This thesis reports the mechanism and resistance to carbon-methanation of active carbon as the support of Ru-based catalyst for ammonia synthesis, the effect of promoter on the carbon-methanation, and the relationship between carbon methanation behavior and the properties of carbon.Among the promoters used, i.e., alkali earth metal, rare earth metal, transitional metal and alkali metal elements, it was found the Sm and Ba are more effective to suppress the carbon-methanation than the others, while the present of K is favorable to carbon-methanation, which can be attributed to the difference of promoter shiftibility and electronegativity.The results of in-suit H₂-TPR-FTIR, XRD and H₂ chemisorption show that the Sm, Ba precursor has been transformed into oxides during activation process. Strong adsorption of hydrogen will improve the carbon-methanation significantly. The experimental results indicate that the presence of Sm, Ba significantly increases the initial temperature of carbon-methanation of Ru/AC. It can be suggested that the interactions among promoters and the surface of support lead to the modification effect on the morphology of Ru/AC, weakening of hydrogen absorption and suppressing the crack of C-CH₃. In particularly, the Sm₂C_1-x characteristic peaks has been observed in XRD patterns of Sm-Ba-Ru-K catalyst, it can be supposed that Sm₂C_1-x would be formed probably due to Sm combine with unsaturated bond of carbon in active carbon, which just is one of witness of the Sm promoter strongly resistibility to carbon-methanation.The carbon-methanation of support of Ru/AC catalyst is highly dependent upon the properties of carbon materials such as degree of graphitization and purity. It is confirmed that the high degree of graphitization and high purity of activated carbon are beneficial to suppress to carbon-methanation.The important reason to result in the carbon-methanation is a structure defect of active carbon with surface carbon unsaturated bond. In the mechanism of carbon-methanation, the cracking of C-CH₃ band may...