Study On Adsorption Characteristics Of Ba Modified Magnesia Supported Ruthenium Catalyst For Ammonia Synthesis

The research of reactant molecules adsorbed on the catalyst surface in heterogeneous catalysis has a great significance in elucidating the nature of the interaction between the reactant molecules and the surface of the catalyst,the catalytic theory as well as the mechanism of the catalytic reaction.Ru-based catalyst is regarded as the second generation of catalyst for the synthesis of NH3 which followed iron catalyst.The adsorption properties of H2 and N2 for activated carbon supported Ru-based catalysts have been studied in great detail at home and abroad.However,the adsorption study on oxide supported Ru-based catalyst has not been reported too much before.Therefore,in view of previous work,we prepared a series of Ba modified magnesia supported Ruthenium catalysts,then used the temperature-programmed desorption(TPD)to study the adsorption of H2 on the Ba modified magnesium oxide supported Ru-based catalysts.We obtained the law that how the properties of supporter affect on the adsorption of hydrogen and provided a theory based on the research and contributed to the development of efficient Ru catalysts for ammonia synthesis.The main research contents and results are as follows:1.In the present experimental conditions,the H2-TPD spectra shows that there are three peaks reflecting three different H2 adsorption state,the position of the peak temperature is at 50-12?,200-300? and 500-600? corresponding to the weak adsorption,moderate-intensity adsorption and strong adsorption for hydrogen adsorbed species,respectively.The hydrogen that has the reactivity of ammonia synthesis mainly concentrates on the moderate-intensity.2.The source of MgO support and the method of doped barium have a great impact on the hydrogen adsorption on the surface of Ruthenium catalysts for ammonia synthesis according to the H2-TPD characterization.This is primarily determined by the physical and chemical properties of MgO support.Compared to the merchandised magnesia,laboratory-made magnesia has larger surface and stronger basicity,which is suitable as the support of the ammonia synthesis catalyst.The prosperities of Ba-MgO support prepared by ultrasonic coprecipitation(SEA)are better than those by stirred coprecipitation(CP)and the dipping method(DI).Ruthenium catalysts on the support prepared by SEA method have highest dispersity,Ru species on it are the most likely to restore,Ru/Ba-MgO catalyst has the strongest adsorption capacity of the moderate-intensity hydrogen and the higher activity for the synthesis of ammonia under the same reaction condition.3.We prepared a series of Ba-MgO supporter modified by glucose and Ru/Ba-MgO catalysts by ultrasonic coprecipitation method(SEA).The results of H2-TPD characterization show that the modification of glucose may affect the hydrogen-absorbing performance on Ru/Ba-MgO catalysts,especially chang the adsorption amount of the moderate-intensity hydrogen.Moreover the changes of glucose concentration can influence the barium content entering into the supportresulting.