Study On The Reduction Performance Of Ru/AC Ammonia Synthesis Catalyst

The Ru/AC catalyst for ammonia synthesis has the advantages of high activity at low temperature,low pressure,and low hydrogen and nitrogen ratio,and so on.Active component ruthenium and additives are loaded on the carrier of the activated carbon by impregnation.Compared with the traditional Fe catalyst prepared by the melting method,the reduction conditions and reaction process parameters are quite different.In order to fully characterize the performance characteristics of the ruthenium catalysts,the influence factors of reduction conditions on the performance of catalysts were studied.The effects of reduction pressure,reduction temperature and heat-resistance time on the activity and structure of ruthenium catalysts were investigated,and the optimized conditions for reduction of ruthenium catalysts were obtained.The stability of the Ru/AC catalysts has always been the key to the industrial application.Based on the optimized reducing conditions,with Ba and K as additives,one or.two rare earth metals were added to prepare Ru/AC catalysts to investigate the influence of stability from La and Sr.The pretreatment of ruthenium catalysts changed the surface functional group of the support and the structural properties of the components.In this study,NH3 and N2 were used to treat the catalyst at high temperature,and the effect of treatment conditions on the surface structure and catalyst performance of the catalyst was investigated.In the experiment,physical adsorption and chemical adsorption(H2-TPR,H2-TPD,N2-TPD,CO chemisorption),mass spectrometry,TEM,IR and Raman were used to characterize the performance and structure of the catalysts.The following conclusions were drawn:The optimization of the reduction conditions had an important effect on the performance of the catalyst.At a certain temperature,as the heat-resistance time increased,the Ru utilization increased.The heat-resistance time reached 4h at 500 ?,and the activity of the catalyst increased from 21.3 vol%to 21.9%vol%.The effect of reduction pressure on the catalyst was not obvious.The reduction temperature had a great influence on the texture properties of the catalyst and the decomposition of additives,which would affected the adsorption properties of the catalysts.When the reduction temperature increased from 400 ? to 510 ?,and the pore volume increased by 53.1%.When the reduction temperature was increased from 400 ? to 500 0C,the increase of the activity was 20.5%.The optimized catalyst reduction conditions were:the reduction temperature of 500 ?,the pressure of 1MPa,the heat resistance-time of 24 h,the low-temperature reduction time of 8 h.The introduction of rare earth metals La and Sr were beneficial to improve the methanation ability of the catalyst.The addition of promoter La or Sr alters the adsorption and desorption of H2 and N2 by the catalyst,which contributes to the desorption of H2,the adsorption of N2,thereby reducing the amount of methane generated by the catalyst and improving the stability of the support.For single additive,1.0wt.%addition amount of La was or 1.5 wt.%of Sr would obtained a better stability of the catalyst.For doubule additives,the thermal stability of the carrier was further improved while the addition amount of La was 0.5wt.%and Sr was 0.5 wt.%.The heat treatment of ammonia and nitrogen affected the texture,surface chemical properties of the catalyst and the desorption capacity of N2 and H2.In the nitrogen heat treatment of the catalyst,the activity of the catalyst showed a downward trend with the increase of heat treatment temperature.When the treatment temperature was 200 ?,the activity of the catalyst was 20.9 vol%.The activity of the catalyst increased first and then decreased with the increase of the ammonia heat treatment temperature ammonia.The activity of the catalyst reached th e maximum of 20.3 vol%at the ammonia heat treatment temperature of 400 ?.Compared with the activity at 200 v,the increase was 10.8%.