Study On The Effects Of Acid-treated Supports On NH₃-SCR Denitrification Performance Of CeO₂/ZrO₂ Catalysts

The exhaust gas from Marine diesel engine contains a lot of nitrogen oxides（NO_x）,which seriously endangers human health and ecological environment.In order to reduce the emissions of NO_x from ships,the International Maritime Organization has formulated increasingly stringent NO_x emission regulations.NH₃-SCR technology has good denitration effect and is widely used in the field of diesel engine exhaust purification.At present,V2O5-WO3 /TiO₂ catalyst is mainly used in Marine SCR denitration system.However,the V-based catalytics are still insufficient in the medium and low temperature range,and the anti-poisoning ability is poor.Therefore,researching and developing a Marine SCR catalyst with wide active temperature window and good anti-poisoning performance is very high research significance and application value.In this thesis,CeO₂/ZrO₂ catalyst was selected as the research object to explore the effect of acid-treated ZrO₂ support on its NH₃-SCR activity and anti-calcium poisoning ability,and characterize and analyze the relationship between catalyst structure and efficiency.The main research achievements are summarized as follows:Firstly,ZrO₂ supports treated with various inorganic acids were prepared by precipitation-impregnation method,and the effects of different inorganic acid treatments on the denitrification performance of CeO₂/ZrO₂ catalyst were compared.The results showed that the SCR performance of CeO₂/ZrO₂ catalyst could be significantly enhanced when adopting sulfuric acid and phosphoric acid treat to ZrO₂ supports.Ce/Zr-S catalyst had a higher NO conversion rate（>90%）in the range of 240⁵00 ℃,and its N2 selectivity was higher than95% in the range of 150⁵00 ℃.This was mainly attributed to the strong surface acidity of Ce/Zr-S catalyst and more abundant Ce³⁺ and Oα species,which were conducive to the oxidation of more NO to NO2,thus promote the "fast SCR" reaction.Secondly,the effects of different molar sulfuric acid treatment of ZrO₂ support on the denitration performance and sulfur resistance of CeO₂/ZrO₂ catalyst NH₃-SCR were further studied,and the relevant reaction mechanism was deeply explored.The results showed that Ce/Zr-0.1S catalyst exhibits good catalytic performance and sulfur resistance.The NO conversion rate of Ce/Zr-0.1S catalyst is about 100 % in the range of 280⁵00 ℃,and the NO conversion rate of Ce/Zr-0.1S catalyst remained above 90 % at 280 ℃ for 16 hours after SO2 was introduced.The characterization results showed that Ce³⁺ and Oα species were more abundant after the ZrO₂ support was treated with proper amount of sulfuric acid,which could promote the "fast SCR" reaction.In situ DRIFTS showed that Ce/Zr catalyst follows E-R mechanism at 250℃ and E-R and L-H mechanism at 350℃.Ce/Zr-0.1S catalyst obeys both E-R and L-H mechanisms at high temperature.Finally,the effect of alkaline earth metal Ca on the denitrification performance of Ce/Zr and Ce/Zr-0.1S catalysts NH₃-SCR were further studied,and the relevant reaction mechanism was deeply explored.The results showed that Ce/Zr-0.1S catalyst showed good anti-calcium poisoning ability.The characterization results showed that the surface of the ZrO₂ support treated with sulfuric acid contains SO42-,which could react with Ca2+ to form Ca SO4,protecting the active species and acid sites of the catalyst.In-situ DRIFTS results showed that Ca could reduces the SCR reaction rate,but did not impact on SCR reaction path on catalyst surface.