The growing demand for light olefins necessitates the development of more efficient and sustainable catalytic processes. Zeolites, with their tunable acidity and shape selectivity, are widely used in hydrocarbon upgrading, where aluminum associated Brønsted acids typically serve as the active sites. However, incorporating less acidic heteroatoms has emerged as a strategy to tune their activity and influence reaction pathways. In this presentation, we discuss our recent work showing how combining gallosilicates and aluminosilicates with distinct zeolite pore topologies (e.g., MWW, CHA, MFI) in a dual-bed reactor enhances production of olefins in the methanol-to-hydrocarbons (MTH) reaction. This configuration uses the less acidic Ga-zeolite upstream as a highly effective dehydration catalyst to convert alcohols to intermediates for downstream upgrading using the Al-zeolite. Here we will discuss recent efforts to elucidate the judicious pairing of zeolites on the basis of Ga speciation and its impact on catalytic performance. To this end, we have used different methods to control gallium speciation via direct synthesis and post-synthesis treatment wherein we assess their performance in tandem MTH reactions with a fixed Al-zeolite (ZSM-5) downstream to establish more robust structure-performance relationships. We have shown that higher Ga loadings promote extra-framework Ga species that suppress C–C coupling, leading to preferential formation of dimethyl ether (DME), while lower Ga loadings with reduced extra-framework Ga promote hydrocarbon production akin to Al-based zeolites. Additionally, we examined the influence of gallium oxide species deposited on siliceous zeolites and mesoporous silicates (benchmark materials). We observed exclusive DME formation over a broad range of Ga loadings, confirming their inability to facilitate hydrocarbon formation. By systematically controlling gallium speciation, this work provides new insights into how different Ga sites influence catalytic pathways in MTH chemistry. Understanding these relationships improves the design of multifunctional zeolites with precisely tailored properties, achieving more versatile and efficient catalysts.
