The NH₃-SCR Performance And Hydrothermal Stability Of One-pot Synthesized Cu-SAPO-34 Catalysts With Different Copper Contents

Ammonia selective catalytic reduction of nitrogen oxides(NH3-SCR)technology is the most efficient technique to eliminate NOx pollution under oxygen enriched conditions.As a representative of Chabazite(CHA)molecular sieve,Cu-SAPO-34 has been widely concerned for its excellent properties such as catalytic activity and hydrothermal stability.In recent years,a new synthetic method called “one-pot” has been found which can introduce the organic copper amine complex directly.This method not only reduces the post processing steps but also controls the copper content easily.Based on this background,this paper explored the effect of copper content of Cu-SAPO-34 on the NH3-SCR performance and hydrothermal stability.The relationship between Cu2+ and activity was also investigated,and the reasons causing the activity loss after hydrothermal treatment was verified.In the present work,different copper content of Cu-SAPO-34 samples were prepared using Cu-TEPA with DEA as co-template by one-pot method followed by hydrothermally aging at 750 oC for 10 h with 10 vol.% H2 O.Several characterization methods were used to investigate the physical structure,the variation of acid sites and the state of copper species of the catalysts.The results show that the copper content in the catalyst increased with the increase of the input of Cu-TEPA and mainly exists in the form of Cu2+ of extra-framework.When the copper content was between 2.66 and 3.62 wt.%,the zeolite catalyst indicated the highest NOx conversion(the active temperature window to achieve 95% NOx conversion is 148-516 oC).When the copper content amounted to 6 wt.%,the high temperature activity of the catalyst decreased.(the active temperature window to achieve 95% NOx conversion had been narrowed to the range between 144 and 420 oC).Non-selective oxidation of NH3 leads to the decline of activity in high temperature.In this case,a large amount of NH3 was consumed while resulting to the deficiency of reducing agent for participating in SCR reaction.After hydrothermal treatment for Cu-SAPO-34 zeolite,the specific surface area,pore volume and acidity had decreased.It was the damage of physical structure and loss of the isolated Cu2+ content that caused the significant activity loss after hydrothermal treatment.When the copper content was 3.62 wt.%,the zeolite catalyst showed the highest NOx conversion(the active temperature window to achieve 95% NOx conversion was between 147 and 450 oC)and hydrothermal stability.