SAPO34

SAPO-34 is a silicoaluminophosphate (SAPO) zeotype that adopts the CHA (chabazite) framework topology. It is part of the SAPO family, which are microporous materials formed by a core of silicon, aluminum, and phosphorus linked by oxygen. In SAPO-34, silicon substitution creates Brønsted acid sites that drive catalytic activity, while the overall framework provides a well-defined, three-dimensional pore system.

The CHA structure in SAPO-34 consists of interconnected cages and eight-membered ring openings, producing a pore network with narrow channels on the order of a few angstroms in diameter. This leads to strong shape selectivity, allowing certain molecules to access the active sites while restricting others. The material is typically used in the hydrogen form or after ion exchange, with the acidity tuned by the Si content in the framework.

Synthesis of SAPO-34 involves hydrothermal crystallization from sources of silicon, aluminum, and phosphorus along with a structure-directing agent that promotes the CHA topology. The resulting material is often converted to the acidic H-form to enable catalysis. Post-synthesis modifications, including framework dealumination or metal doping, can adjust stability and activity for specific reactions.

The primary application of SAPO-34 is in methanol-to-olefins (MTO) processes, where it demonstrates high selectivity for light olefins such as ethylene and propylene. Its small-pore CHA structure imparts strong shape selectivity and resistance to side reactions that produce heavier aromatics. SAPO-34 remains a focus of both industrial deployment and academic research, with ongoing work to enhance stability, scalability, and performance in various reaction environments.