Spotlight on Cu/SAPO-34 with high hydrothermal stability induced by a small amount of SSZ-39

Abstract

The stable structure is key to improving the performance of the selective catalytic reduction of nitrogen oxide (NOx) with ammonia (NH3-SCR) on Cu/zeolite catalysts after the high-temperature hydrothermal aging. In this work, the SSZ-39 seed with a stable texture property was introduced into the precursor of SAPO-34 to fabricate the zeolite with a hybrid microstructure of SAPO-34 + SSZ-39 (simplified as SA + SZ). The Si distributions of the original Al-rich SAPO-34 zeolite (simplified as SA) were optimized by the hybrid microstructure of SA + SZ. The results of solid nuclear magnetic resonance (NMR) and ammonia (NH3) adsorption indicate more Si(1OAl) structures with strong acidity on Cu/(SA + SZ) catalyst rather than on Cu/SA. The NH3-SCR performance within the reaction region of 150–550 °C is enhanced on the former. In addition, the Si(nOAl) (n = 2–4) structures of the original SAPO-34 zeolite are retained on Cu/(SA + SZ), which optimizes the low-temperature catalytic performance of Cu/SSZ-39. Furthermore, the SSZ-39 seed induces Cu/(SA + SZ) to form higher content of stable Si(0OAl) structures than Cu/SA. After hydrothermal aging, more isolated copper species can be formed on SA + SZ hybrid zeolite with advanced structural stability compared with Cu/SA, which better activates NOx on the former. And the loss of acid sites is also weakened on Cu/(SA + SZ) than on Cu/SA. These improvements on Cu/(SA + SZ) compensates for its hydrothermal deactivation to some degree. Hence, SA + SZ hybrid zeolite can be the new-generation candidate for NH3-SCR catalyst by introducing the second zeolite SSZ-39 in the synthesis process of SAPO-34. And the catalytic performance of Cu/(SA + SZ) is superior to Cu/SA.