Research On NH₃-SCO Catalysts For Diesel Vehicle Exhaust

The technology of selective catalytic reduction of nitrogen oxides（NH₃-SCR）using ammonia（NH₃）as reducing agent is the mainstream technology of diesel vehicle tail gas NOx treatment at present.In order to achieve the complete conversion of NO,SCR treatment process needs to inject vehicle urea to produce equal or excess NH₃ to reduce NOx,but in practical application,there will be a small amount of ammonia reaction is not complete,so it will cause NH₃ slip.NH₃ is a colorless,strongly odorous and corrosive gas,which will cause serious harm to the natural environment and human health.As the national emission standards for diesel engines become more and more stringent,the removal of leaked ammonia has attracted more and more attention.At present,selective catalytic oxidation of ammonia（NH₃-SCO）is considered to be the most promising technology for the treatment of leaking ammonia,and the core of this technology is the catalyst.the SCO catalyst with high catalytic activity,high N₂selectivity and good hydrothermal stability has attracted widespread attention.In this paper,the Cu-based catalyst was used as the research object,the Co-Cu/Beta catalyst with good catalytic activity at low temperature was obtained by bimetallic element doping modification,and then SSZ-13 was used as the carrier,and its catalytic performance was investigated.XRD,SEM,TEM,FTIR,H₂-TPR and NH₃-TPD were used to further analyze the reasons for the increase of SCO catalytic activity and the reason for the decrease of SCO catalytic activity after hydrothermal treatment.The research contents include:（1）The Cu/Beta catalyst was prepared and the effects of copper loading,preparation method,calcination temperature reaction space velocity and hydrothermal aging treatment on the reaction performance were investigated.it was found that when the space velocity was 36000 h^-1,the calcination temperature was 450℃and the copper loading was 10 wt%,the catalytic effect of Cu/Beta catalyst was the best.the ammonia conversion reached 62%at 250℃,the ammonia conversion was as high as 93%at300℃,and the N₂ selectivity was not less than 90%in the whole temperature range.The amount of copper loading will affect the catalytic activity and N₂ selectivity,which is related to the existing state of copper oxide components.After hydrothermal treatment,the activity of the catalyst decreased slightly at low temperature due to the destruction of the molecular sieve framework to a certain extent.（2）The ammoxidation catalyst supported by bimetallic elements was prepared.It was found that the catalytic effect of Co element doping was the best.The effects of impregnation method,Co loading and hydrothermal aging treatment on the reaction performance were investigated.When the cobalt loading of the Co-Cu/Beta catalyst is4 wt%,the NH₃ conversion can reach 92%at 250℃,and the N₂ selectivity is more than80%in the whole temperature range of 150℃to 400℃,which is mainly due to the cobalt doping promoting the dispersion of copper oxide species,the increase of acidic sites and the enhancement of redox ability.After hydrothermal treatment,the catalytic activity of Co-Cu/Beta decreases obviously,mainly due to the doping of Co element and the production of copper aluminate after hydrothermal treatment,the redox ability becomes weaker and the ammonia adsorption capacity becomes worse.（3）The Cu/SSZ-13 and Co-Cu/SSZ-13 catalysts were prepared,and it was found that the catalytic activity of the fresh catalyst Cu/SSZ-13 was better than that of the Co-Cu/SSZ-13 catalyst,but after hydrothermal treatment,the catalytic activity of the Co-Cu/SSZ-13-HT catalyst was better,and the conversion efficiency could still reach more than 90%at 300℃.