(601b) Pairing Ga- and Al-Zeolites with Tailored Acidity As Tandem Catalysts for Alcohol-to-Olefin Conversion

Zeolites serve as versatile catalysts due to their tunable acidity, where active sites can be placed within the crystal framework or as extra-framework species in confined pores. A widely used method for tailoring Brønsted acidity involves heteroatom exchange, where framework aluminum is substituted with alternative elements. The introduction of heteroatoms often yields catalysts with reduced acidity, suitable for sequential reactions targeting specific reactive intermediates. In this presentation, we will describe recent studies where a series of three distinct zeolites with MWW, CHA, and MFI frameworks were synthesized as aluminosilicates and gallosilicates to assess their performance in alcohol dehydration reactions, specifically methanol conversion to dimethyl ether and ethanol conversion to ethylene. Our results indicate that Ga-MCM-22 (MWW) exhibits exceptional performance achieving nearly 100% alcohol conversion and selectivity toward desired products at significantly reduced contact times compared to previous reports. The performance of Ga-zeolites can be attributed to their reduced acid site strength, facilitated by a one-pot synthesis method that avoids conventional post-synthesis modifications. We demonstrated the application of Ga-zeolites as tandem catalysts when paired with a downstream Al-zeolite in a dual-bed reactor configuration to convert alcohols into valuable intermediates, leading to increased production of light olefins. Our findings reveal that dual-bed configurations using Ga-zeolite/Al-ZSM-5 (upstream/downstream) pairings outperform single-bed configurations using Al-ZSM-5 in methanol to hydrocarbons reactions, with notable improvements in catalyst lifetime and light olefins selectivity. Similarly, dual beds using Ga-zeolite/Al-SSZ-13 (upstream/downstream) pairings exhibit superior performance in ethanol to propylene reactions, with significant increases in propylene selectivity (>20%) compared to conventional single beds of Al-SSZ-13. This research offers a unique perspective on heteroatom-exchanged zeolites in tandem reactions by leveraging their modified acidity and suggesting variations in intrinsic acidity within the zeolite crystal structure.