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Destructive and Protective Effects of NH 3 on the Low-Temperature Hydrothermal Stability of SAPO-34 and Cu-SAPO-34

2022; American Chemical Society; Volume: 14; Issue: 38 Linguagem: Inglês

10.1021/acsami.2c13890

1944-8252

Yue Ma, Yang Gao, Xiaodong Wu, Baofang Jin, Rui Ran, Zhichun Si, Duan Weng,

Catalytic Processes in Materials Science

The influences of gaseous, weakly adsorbed, and strongly adsorbed NH3 on the low-temperature (<100 °C) hydrothermal stability of SAPO-34 and Cu-SAPO-34 were investigated. NH3 temperature-programmed desorption (NH3-TPD), 1H magic angle spinning nuclear magnetic resonance (MAS NMR), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were adopted to characterize the adsorption states of NH3 and H2O in SAPO-34, and the destruction of the SAPO-34 framework was revealed by direct and cross-polarization 29Si, 27Al, and 31P MAS NMR. Gaseous NH3 coadsorbed with H2O inside SAPO-34 micropores and induced the hydrolysis of framework P-O-Al and Si-O(H)-Al bonds. Weakly adsorbed NH3 was released during aging and played a similar negative role to gaseous NH3. When being combined with hydrolyzed Al species from the framework, active Cu ions transformed to inactive CuAl2O4-like species, leading to deactivation in low-temperature SCR of Cu-SAPO-34. Strongly adsorbed NH4+ via 200 °C preadsorption protected the framework integrity of SAPO-34 and the SCR activity of Cu-SAPO-34.