Effects of the Template on Low-Silica SAPO-34 in a Bifunctional Catalyst for the Direct Conversion of Syngas to Light Olefins

ABSTRACT: Bifunctional catalysts composed of metal oxides and zeolites have become a promising method for direct conversion of syngas into light olefins recently. To maintain high selectivity of light olefins in syngas direct conversion, a series of low-silica SAPO-34 zeolites were synthesized hydrothermally with three templates including triethylamine (TEA), tetraethylammonium hydroxide (TEAOH), and a mixture of TEA and TEAOH. The characterization results indicated that the crystallinity, acidity, structure, and morphology of zeolites would be greatly affected by the templates. Compared with the single templates, low-silica SAPO-34 prepared with the dual template possessed suitable acidity, higher crystallinity, and regular morphology, thus exhibiting higher selectivity of light olefins. The bifunctional catalyst consisting of ZnCrOx and SAPO-34 prepared using the dual template with a Si/Al molar ratio of 0.025 achieved a C2=???C4= selectivity of 76.1% and a CO conversion of 39.9% at 4 MPa and 5400 mL g???1 h???1. These results demonstrated that it is crucial to control the structure and acidity of zeolites in the design of bifunctional catalysts with excellent shape selectivity for syngas conversion to olefins.