Deactivation Mechanism Based On Carbon Gasification For Carbon-supported Ru-based Ammonia Synthesis Catalyst And Its Application

The application of Ru catalyst supported on active carbon is arguably the most significant advancement following the work of Haber and Bosch in ammonia synthesis.However,the insufficient stability of carbon-supported ruthenium catalysts greatly limits their industrial application,and carbon methanation is often considered as the key reason for deactivation.But all strategies for decreasing the methanation of carbon can not fully solve the deactivation problem of carbon-supported ruthenium catalysts.Therefore,the investigation of the deactivation mechanism of Ru catalyst and the preparation of the high efficient carbon-supported ruthenium catalyst were the great challenges in the field of ammonia synthesis.Based on our previous research that CO would form during the heat treatment of carbon-supported ruthenium catalysts at high temperature,this thesis intends to investigate the effect of promoters on the catalytic activity and the thermal stability of carbon-supported Ru catalyst.The gasification loss of carbon and its effect on the catalytic performances would be studied.The relation between the properties of carbons and the performances of carbon-supported Ru catalyst also was investigated.Then the high efficient carbon-supported Ru catalyst performance would be prepared using the product of carbon gasification reactions.The results and conclusions are summarized as follows:(1)There is no clear correlation between carbon methanation and the loss of activity.Carbon loss,especially via carbon oxidation,led to the increase of Ru particle size,and then active sites available for hydrogen desorption at low temperature would decreased greatly.As a result,the catalytic activity and the stability of Ru/C catalysts decreased significantly.(2)The properties of carbons have a strong influence on the activity and stability of carbon-supported Ru catalysts with Ba promoter.Various factors,including surface area,oxygen-containing functional groups and the ratio of micropores of carbon all affected the dispersion of Ru particles.The presence of larger number of the oxygen functional groups would inhibit the migration of hydrogen atoms,and then the promoter reduction or the ammonia synthesis activities would also be affected.The presence of oxygen functional groups may affect the thermal resistance of ruthenium catalysts,but carbon supports with an appropriate amount of oxygen-containing functional groups increased rather than decreased the thermal stability and the activity of carbon-supported Ru catalyst.(3)A highly efficient carbon-supported ruthenium catalyst can be prepared by Carbon monoxide treatment of carbon-supported Ru catalyst with Ba promoter at 500 ?,which would introduce carbon and the groups of anhydride and esters groups.Then hydrogen adsorption properties would be changed,and ammonia synthesis activity increased significantly.The formation carbon,which obtained by CO treatment,is more easily gasified to form methane or other carbon-containing gases.Therefore,the structure of carbon support would be protected,and then the as-obtained ruthenium catalyst showed a good thermal stability.This work provides a new general strategy for the preparation of various metal catalysts supported on carbon with high efficiency.This finding will not only help to solve the problem of the stability of carbon-supported Ru catalyst,but also contribute to design and prepare carbon-supported metal catalysts with high activity and stability using in ammonia synthesis or other catalytic filed.