Reduction Of NO_x In Coke Oven Flue Gas On MnCeSAPO-34 At Low Temperature

The coke oven flue gas produced by coal coking will produce a large amount of NO_x,followed by a large amount of SO₂ and H₂O.NO_x emissions cause a lot of environmental problems,such as the formation of acid rain,the impact of photochemical smog and the global warming caused by the greenhouse effect.A large number of studies have proved that NH₃ selective catalytic reduction of NO_x technology（NH₃-SCR）is one of the most effective ways to remove fixed source NO_x,and the catalyst is the key to this process.Therefore,it is necessary to develop a new type of low-temperature catalyst and have better anti-poisoning ability.In this thesis,SAPO-34 was selected as the carrier in the catalyst preparation process,and the active components Mn and Ce were supported as the metal components in the framework of SAPO-34 to prepare a MnCeSAPO-34 molecular sieve catalyst with a microporous structure.The catalyst showed good NO_x catalytic activity at low and medium temperatures（150-300℃）.Because the coke oven flue gas contains a large amount of SO₂ and H₂O.Based on the MnCeSAPO-34 catalyst,the anti-SO₂ and H₂O poisoning performance of the catalyst was clarified.To widen the active temperature range of the catalyst and further improve the low-temperature NH₃-SCR denitration activity of the catalyst.Solvents,templating agents,and surfactants were used to modify the catalyst preparation during the preparation of MnCeSAPO-34.It was envisaged to increase the specific surface area of the catalyst to increase the denitration activity of the catalyst,and evaluate and characterize the prepared catalyst.The specific results are as follows:（1）In situ synthesis of MnCeSAPO-34 molecular sieve catalyst using diisopropylamine as a template,compared with the traditional impregnation method and co-precipitation method to support metal components,Mn and Ce and SAPO-34 are supported in situ to make the metal element distribution More even.The catalyst has a large specific surface area,which facilitates the adsorption,desorption,diffusion,and transfer of reactant molecules.Compared with SAPO-34 molecular sieve that supports metal components,the catalyst carrier is integrated with the active component.At the same time,the catalyst has more acid sites and better redox properties and has more surface adsorbed oxygen（Oα）,Mn⁴⁺and Ce³⁺,these are all conducive to promoting the conversion of NO to NO₂,thereby promoting a rapid SCR catalytic reaction.In situ infrared results show that during the reaction of the MnCeSAPO-34 catalyst,NH₃ at the Lewis acid site plays a major role,and NH₃ reacts with polydentate nitrate after monodentate nitrate.（2）MnCeSAPO-34 catalyst has certain anti-H₂O,anti-SO₂ and anti-H₂O+SO₂performance.Under the action of H₂O,the catalyst always maintains good catalytic activity,and the microporous structure of the catalyst remains stable.The hydroxyl groups in H₂O will form protonic acids,which will increase the number of Br?nsted acid sites,and the number of Lewis acid sites will not decrease.The addition of SO₂ caused the deposition of ammonium sulfate on the catalyst and the specific surface area decreased.NO_x decomposition temperature peak of the metal ammonium sulfate was found in MnCeSAPO-34.The metal component was not poisoned by the metal component at 6 h.Oα,Mn⁴⁺and Ce³⁺all decreased.When H₂O+SO₂ coexisted at 180℃,the activity of the MnCeSAPO-34 catalyst decreased by 19%.When SO₂ and H₂O were stopped from entering the atmosphere,the NO_x conversion rate returned to 94%.（3）For the preparation process of MnCeSAPO-34 molecular sieve,the solvent and template agent were changed during the catalyst preparation process to increase the specific surface area of the catalyst and thus increase the SCR activity of the low-temperature catalyst.The test results show that when the solvent H₂O is replaced by ethanol,the greater the amount of ethanol,the smaller the specific surface area of the catalyst and the larger the average pore size.The worse the denitration activity of the catalyst and the physical and chemical properties of the catalyst change.When the cationic surfactant CTAB was added during the preparation,the specific surface area of the catalyst decreased slightly,indicating that the addition of CTAB had a suppressive effect on the increase of the specific surface area of the catalyst.When triethylamine was added to replace part of diisopropylamine as a template in the catalyst preparation process,the prepared catalyst had a larger specific surface area than MnCeSAPO-34.The NH₃-SCR denitration activity test also proved that the increase in the specific surface area of the catalyst made the low temperature activity has seen an increase.