Investigation On Decomposition And Reactivity Of NH₄HSO₄ On The Surface Of SCR Catalysts

Selective Catalytic Reduction?SCR?is the main technology of flue gas denitrification.However,ammonium bisulfate?ABS?is inevitably formed on the catalysts by sulfur oxides,water vapor and reductive ammonia in the flue gas in the intermediate and low-temperature SCR process.Ammonium bisulfate blocks the pore structure,and covers the active site of catalysts and causes a decrease of denitrification activity.Therefore,reducing the deposition of ammonium bisulfate on the catalysts is a key factor for the industrialization of intermediate and low-temperature SCR technology.The effects of WO₃ content and active promoters MoO₃,Sb₂O₃ and CeO₂ in V₂O₅/TiO₂ catalyst on the decomposition and reactivity behaviors of ammonium bisulfate were studied by means of transmission FTIR,XPS,TGA,TPDC and In Situ DRIFTS.Finally,the regeneration experiments of poisoned V₂O₅-WO₃/TiO₂ catalyst were carried out.The main results were as follows:The effect of WO₃ loading on the decomposition and reactivity behaviors of ammonium bisulfate on the V₂O₅/TiO₂ catalyst was studied.The results showed that when ammonium bisulfate was loaded on the V₂O₅-WO₃/TiO₂ catalyst,there was the chemical interaction between ammonium bisulfate and the catalyst,and the chemical bond was formed between them.WO₃ promoted the decomposition and reactivity behaviors of ammonium bisulfate,specifically by reducing the decomposition temperature of ammonium bisulfate and promoting the reactivity behavior of NH₄⁺and NO in ammonium bisulfate.The higher the WO₃ loading,the better the decomposition and reactivity behaviors of ammonium bisulfate.Moreover,the sulfur and water resistance of the catalyst were consistent with the decomposition and reactivity behaviors of ammonium bisulfate.The effect of active promoters MoO₃,Sb₂O₃ and CeO₂ on the decomposition and reactivity behaviors of ammonium bisulfate on the V₂O₅/TiO₂ catalyst was studied.Compared with Sb₂O₃ and CeO₂,the more easily the chemical bond between ammonium bisulfate and MoO₃ broke,the more easily ammonium bisulfate decomposed,which was manifested by reducing the decomposition temperature and increasing the decomposition rate of ammonium bisulfate.Meanwhile,MoO₃ had the strongest promotion effect on the reactivity behavior of ammonium bisulfate,which accelerated the reactivity of NH₄⁺and NO in ammonium bisulfate.MoO₃ significantly improved the catalytic activity,sulfur and water resistance at low temperature,which provided a theoretical basis for the selection of intermediate and low-temperature SCR catalysts in the industry.The effects of thermal regeneration and thermal reduction on the regeneration of poisoned V₂O₅-WO₃/TiO₂ catalyst were studied.The results of the activity test showed that regeneration temperature was the critical factor which affected the regeneration effect of poisoned catalyst.The regeneration effect of thermal regeneration was better than that of thermal reduction,but neither of them completely restored the denitrification activity.Combined with characterization analysis,it was found that the SO₂ produced by the decomposition of ammonium sulfate on the catalysts reacted with the active component to form metal sulfate or reacted with reducing gas NH₃ to form ammonium sulfate again,resulting in the reduction of active components or the coverage of active sites.