Effect of Different Structure Directing Agents on Deactivation of Cu/SAPO-34 during Low-Temperature NH3-SCR

Cu/SAPO-34 and Cu/SSZ-13 having CHA structure have attracted significant attention because of their high activity and N₂ selectivity during SCR reaction as well as superior hydro carbon resistance. The Cu/SAPO-34 has shown better hydrothermal durability than Cu/SSZ-13 at high temperature [1]. However, we have earlier observed that Cu/SAPO-34 prepared by the morpholine route deteriorated under water exposure at low temperature, where the activity decreased from 87% conversion to 6% conversion after 9 h of low temperature experiment [2]. Nevertheless, there is still a lack of understanding of the deactivation mechanism of Cu/SAPO-34 during low temperature NH₃-SCR reaction.

In this study, Cu/SAPO-34 using three different templates, i.e., morpholine(MO), trimethylamine (TEA), and tetraethylammonium hydroxide (TEAOH), as structure directing agent were prepared by incipient wetness impregnation (IWI) method. Characterizations of those catalysts suggest that they have different physical/chemical properties as well as various species of Cu. For example, analysis of H₂-TPR profiles of Cu/SAPO-34 catalysts proposed that they contain different amount of Cu species depending on the structure directing agents. Those catalysts were systematically investigated for low-temperature NH₃-SCR system under water exposure in order to find the correlation of their chemical/physical structures and deactivation. It was observed that the activity of Cu/SAPO-34 declined when they were exposed to water at low temperature as observed in the previous study [2]. Interestingly, deactivation of Cu/SAPO-34 catalysts behave differently depending on the choice of template. Additionally we found that activity of Cu/SAPO-34 using MO as template after water exposure at low temperature declined regardless of a variety of regeneration methods including a dry atmosphere at 600 °C. To conclude, the choice of template over Cu/SAPO-34 catalysts significantly influence their activities and deactivation during low temperature NH₃-SCR.

[1] D.W. Fickel, E. D’Addio, J.A. Lauterbach, R.F. Lobo, Appl. Catal. B: Environ. 102 (2011) 441-448

[2] K. Leistner, L. Olsson, Appl. Catal. B: Environ. 165 (2015) 192-199