Generating nanocrystalline SAPO-34 through bead-milling and porogen-assisted recrystallization: Structural evolution and catalytic consequence in dimethyl ether-to-olefin conversion

Abstract

Mechanochemical bead-milling is a promising post-synthetic way to generate nanocrystalline zeotype materials with promoted catalytic performance. Post-milling recrystallization is often entailed to remedy the damaged framework but leads to crystal growth. Herein, using SAPO-34 (ca. 20 µm) derived from inexpensive morpholine as an example, we showcase that secondary growth can be suppressed by porogen-assisted recrystallization, resulting in formation of tiny crystals (100–200 nm) with better mass transport property. The presence of porogen (polydiallyldimethylammonium chloride) also induced a reduction of acid site density owing to a re-distribution of Si across the crystal, which alleviated zoning of Si at the external surface. The catalytic advantages, with respect to a control sample recrystallized in the absence of porogen, have been experimentally verified in dimethyl ether-to-olefin conversion, exhibiting an exaggerated light olefin selectivity and prolonged catalyst lifetime. This advancement of mechanochemical synthesis opens an avenue to better tailor crystal size for zeotype materials.