Study On Application Of Coating SCR Catalyst In Diesel Exhaust

The attention of air pollution is gradually increasing.The ship diesel engine gives a considerable part of NO_x emissions among the NO_x pollution caused by human activities.Selective catalytic reduction?SCR?technology is used in off-board purification technology to control the NO_x emissions from ships.The catalyst is the technical core of the SCR system.The commercial SCR catalysts mainly use vanadium-based catalysts due to the high S content of ship diesel.In this paper,a vanadium-based catalyst was prepared by adding silica sol coating type V₂O₅-WO₃/TiO₂-SiO₂/cordierite catalyst.And the catalysts by coating Cu/SAPO-34/cordierite catalyst and coating Cu/SSZ-13/cordierite catalyst by one-step impregnation were prepared.Then their NH₃-SCR performance were studied.The coating V₂O₅-WO₃/TiO₂-SiO₂/cordierite sample catalyst was prepared by a one-step impregnation method.The intrinsic kinetics of the catalyst was investigated using a power-exponential function model.The reaction orders of NO,NH₃ and O₂ were 0.93,0,0.24.The final activation energy is E=25.99 kJ/mol.Then the catalyst was enlarged.A coated V₂O₅-WO₃/TiO₂-SiO₂/cordierite industrial grade sample was prepared through the optimization of the experimental process.And the mechanical properties,catalytic performance and the industrial grade sample was characterized.The results showed that the specific surface area of cordierite after cordierite treatment increased from 0.09 m²/g to82.59 m²/g with more mesopores appeared.The specific surface area of cordierite after treated with cordierite was only 28.29 m²/g.And a large number of mesopores was appeared.The appearance of mesopores is conducive to NH₃-SCR reaction.The small test catalyst can all reach over 20%coating amount after three times of coating.The industrial coated catalyst has a NO_x conversion efficiency of 80%at 300°C to 500°C through the detection of a testing organizations.Different supports?ZSM-5,SSZ-13,SAPO-34,KIT-6,?zeolite,Y zeolite and mordenite?were screened by impregnation method with 2%Cu.SAPO-34 and SSZ-13showed the best NH₃-SCR activity.The effects of Cu content,preparation method,anti-aging properties and the activity of NH₃-SCR of Cu/SAPO-34 catalyst were studied.The Cu/SAPO-34/cordierite catalyst prepared by one-step impregnation method.The number of coating,the coating method,the type of binder?acidic silica sol,alkaline silica sol,alumina sol?,the addition of dispersant and other factors on the activity of NH₃-SCR were studied.The final results show that the coated Cu/SAPO-34 catalyst with 17%acidic silica sol as binder has the best performance with over 95%NO conversion efficiency in the range of 200 ^oC⁴25 ^oC with a rate of 16.89%.Dispersant additions only improve high temperature performance.The Cu/SSZ-13 catalyst prepared by different methods?impregnation method,equal volume impregnation method and ion exchange method?showed the best denitrification effect of 3%Cu/SSZ-13 prepared by the same volume impregnation method.And it hydrothermal aging performance was studied.Finally verified the NH₃-SCR performance of SSZ-13 catalyst by one-step impregnation method.