Cu/SAPO-34 catalysts have been reported to show much improved activities and durability than previous generation catalysts for effective NOx emission reduction via selective catalytic reduction (SCR). SAPO-34 is a crystalline silico-alumino-phosphate chabazite structure zeolite with regular micropores (0.38 nm), and it has demonstrated excellent hydrothermal durability at temperatures up to 800°C. The work aimed to understand the NO/NH3 adsorption/desorption behavior and to provide insights to understanding NH3-SCR reaction mechanism. In this study, Cu/SAPO-34 was prepared by an ion exchange method and its NH3-SCR activity as well as chemisorption properties was evaluated. Superior NH3 adsorption ability of Cu ion-exchanged SAPO-34 was observed, in comparison with NO. NH3 can be adsorbed on both Cu ion sites and Brønsted acid sites. Cu exchange enhances the low temperature NH3 adsorption ability by introducing more Lewis acid sites, but reduces Brønsted acidity of zeolite, whereas adsorbed NH3 species have higher thermal stability. Transient experiments using both flow-through reactor and Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were performed to identify the active sites for NH3-SCR reaction and reactivity of different adsorbed species on the catalyst. Ion-exchanged Cu sites were found to be more active for NH3-SCR reaction and Brønsted acid sites in SAPO-34 were the source of NH3 species for NH3-SCR reaction, which played an important role especially at high temperatures.

New insights into NH3/NO chemisorption properties and NH3-SCR reaction mechanism over Cu/SAPO-34 as NH3-SCR catalysts

254th National Meeting (2017)

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