The self-protection effect of reactant gas on the moisture stability of CuSAPO-34 catalyst for NH3-SCR

Abstract

The surface of CuSAPO-34 catalysts after NH3-SCR reaction (T ≤ 400 °C) is revealed to have residual adspecies. Cycle hydration methods are designed to explore the influence of the residual species upon the moisture stability of CuSAPO-34. It is demonstrated that the residual species on the catalyst surface are NH3 adspecies, which could help inhibit the transformation of Si(OAl)4 species to Si islands and prevent the decay of Brönsted acid sites (BAS) during the hydration treatment; the better preserved acidity and the existence of NH3 facilitate the preservation of isolated Cu2+ ions and their reducibility, and thus the SCR activity of the catalysts. The protective effect of residual NH3 species against the low-temperature water vapor is prominent when T ≤ 300 °C, which declines gradually and becomes weak when T > 400 °C due to the desorption of NH3 adspecies. The present work implies that the moisture stability of CuSAPO-34 catalyst could be simply ameliorated by locating it in an appropriate zone of the tailpipe to avoid the excessive desorption of the NH3 adspecies.