The effect of crystallite size on low-temperature hydrothermal stability of Cu-SAPO-34

Abstract

Two Cu-SAPO-34 samples with similar chemical compositions but different crystallite sizes of 10 μm and 2 μm, respectively, were obtained by modifying crystallization conditions. The effect of crystallite size on the low-temperature hydrothermal stability of Cu-SAPO-34 was comparatively investigated. The results showed that Cu-SAPO-34 with smaller particle size possessed better resistance to treatment at 70 °C in humid conditions. During low-temperature hydrothermal aging, isolated Cu²⁺ species in Cu-SAPO-34 tended to be attacked by water vapor to form Cu(OH)₂ species, which can combine with extra-framework Al to form inactive CuAl₂O₄ species. The superior stability of Cu-SAPO-34 with smaller crystallite size is primarily attributed to the lower Cu concentration on the crystal surface compared with the sample with larger particle size. Thus, more active Cu sites were maintained on small-size Cu-SAPO-34 after low-temperature hydrothermal aging.