Rational Design of SAPO-34 Zeolite in Bifunctional Catalysts for Syngas Conversion into Light Olefins

Zeolites in bifunctional catalysts composed of a metal oxide and a zeolite (OX-ZEO) play a crucial role in conversion of generated intermediates during the reaction. In this work, a series of SAPO-34 zeolites were hydrothermally synthesized using different templates, i.e., morpholine (MOR), diethylamine (DEA), tetraethyl ammonium hydroxide (TEAOH), and their mixture. The effects of templates, SiO2/Al2O3 molar ratios on the zeolite structure, and surface properties were investigated, and the catalytic performance over SAPO-34 combined with GaZrOx oxide for the conversion of syngas into light olefins was explored. SAPO-34 synthesized using a MOR or DEA template exhibits large particle sizes, while the TEAOH or TEAOH-contained templates contribute to the small particle size and large specific surface area. SAPO-34 with small particle sizes benefits to enhance the CO conversion and C2–4= selectivity, and the increase in Brønsted acid site amounts slightly reduced the C2–4= selectivity when the particle size of SAPO-34 is small and varied a little. SAR0.4-TD with a SiO2/Al2O3 ratio of 0.4 exhibits the highest space–time yield of light olefins of 261.0 mL·h–1·g–1 at a CO conversion of 28.0%. Moreover, the carbon deposition and the evolution of carbonaceous species for the spent GaZrOx/SAPO-34 catalyst were studied to analyze the reason for catalyst deactivation.