A Green and Cost-Effective Synthesis of Hierarchical SAPO-34 through Dry Gel Conversion and Its Performance in a Methanol-to-Olefin Reaction

Rapid and Effective Way to Synthesize Highly Crystalline Nanosized SAPO-34 Particles

SAPO-34 nanocrystals with sizes of 50-150 nm were obtained via steam-assisted crystallization (SAC) for 5 h at 200 °C from two types of aluminum precursors-aluminum isopropoxide and boehmite. A reaction mixture composition with a small amount of organic template tetraehylammonium hydroxide (TEAOH) was used with the molar ratio TEAOH/Al₂O₃ = 1/1. The alumina precursor type and duration of the SAC (5 and 24 h) on the crystal size, texture, and acid properties were investigated. The SAPO-34 nanocrystals that we obtained possess a large micropore volume of 0.22-0.24 cm³/g and a specific surface area of 651-695 m²/g. When the crystallization was prolonged for up to 24 h, a SAPO-18 structure appeared, but the micropore and mesopore volumes changed insignificantly. Using boehmite as the aluminum precursor led to higher mesoporosity of the material but a little bit lower acidity when compared with the samples prepared from aluminum isopropoxide. In addition, the method proposed was used for preparing a SAPO-34-coated aluminum adsorber heat exchanger. Thus, the synthesis method proposed is affordable and effective to prepare SAPO-34 highly crystalline nanoparticles, with no need for post-synthetic procedures as the mother liquor separation from nanocrystals.