Preparation And Mechanism Of Anti-poisoning Ce-Based Catalysts For NH₃-SCR Of NO_x

The nitrogen oxides emitted by motor vehicles and the combustion of fossil fuels will cause many environmental problems,such as acid rain,smog,photochemical smog and so on,which will harm the health of plants and animals and cause property losses.Therefore,it is imperative to control the man-made emission of nitrogen oxides.Among a variety of nitrogen oxide emission control technologies,NH₃-SCR technology is the most effective and widely used,and efficient catalyst is the key to the application of this technology.At present,the most widely used commercial catalyst is vanadium-tungsten-titanium catalyst,which has high activity and resistance to sulfur poisoning,but it also has some problems,such as low selectivity at high temperature,poor alkali resistance and so on.In addition to NO_x,there are also alkali metals,heavy metals,phosphorus and other harmful substances in the flue gas,causing catalyst poisoning and deactivation.Therefore,it is the focus of the current research on denitrification catalysts to develop catalysts with high activity and high resistance to toxic chemicals and to explore their mechanism.In this paper,a highly effective anti-poisoning denitrification catalyst was designed and prepared from the point of view of selecting acidic precursors,adding promoters and selecting strong acidic carriers.The anti-poisoning mechanism of the catalyst was studied systematically with the help of a variety of characterization methods.The content of this paper is as follows:?1?Layered zirconium phosphate was prepared by sol-gel method and used as catalyst carrier to synthesize supported Ce O₂/Zr?HPO₄?₂catalyst.Due to the strong acidity of zirconium phosphate,the catalyst has high catalytic activity,and the activity has hardly not decreased after 1%potassium poisoning.It was found that the catalyst did show a layered structure by SEM,and the results of EDS line scan showed that the content of Ce on the surface of the catalyst was much less than that of K,indicating that most of the active components of the catalyst entered the bulk phase of the catalyst,and it was inferred that the active components entered the interlayer.Due to the dual protection of strong acidity and workshop function,the catalyst has good anti-poisoning ability.?2?Zeolite-like amorphous Ce-Si₅Al₂O_x catalysts were prepared by using strongly acidic nano-zeolites as precursors.The activity and resistance to potassium poisoning,phosphorus poisoning as well as phosphorus and potassium co-poisoning of this catalyst were compared with those of supported Ce O₂/Si₅Al₂O_x catalyst and Ce-beta catalyst.The results show that Ce-Si₅Al₂O_x catalyst has the same activity as molecular sieve and excellent alkali metal resistance.Because of the unique structure of the Ce-Si₅Al₂O_x catalyst,it is easier for the poisonous substance potassium and phosphorus to combine with the silicon site,thus protecting the active components bound to the aluminum site and making the catalyst has a better ability to resist potassium and phosphorus co-poisoning.In contrast,the activity and resistance to potassium and phosphorus poisoning of Ce O₂/Si₅Al₂O_xcatalyst are poor.Ce-beta catalyst has excellent SCR performance and resistance to potassium poisoning,but phosphorus poisoning seriously affect the structure and redox property of the catalyst,resulting in serious irreversible deactivation.?3?The Ce Cu-Si₅Al₂O_x catalyst with two active components was synthesized by cerium exchange followed by one-step copper exchange.Compared with the single-component Ce-Si₅Al₂O_x catalyst,the catalyst has better low-temperature activity,sulfur resistance and hydrothermal aging resistance.The exchange of Cu may lead to the occupation of some silicon hydroxyl groups on the catalyst,thus reducing the alkali metal resistance of the catalyst.However,this catalyst still has better resistance to potassium poisoning than the normal catalyst.The resistance to heavy metals of the catalyst was investigated,and it was found that the catalyst also had a certain resistance to heavy metals.