Stable methanol-to-DME conversion in catalytic membrane contactor enabled by bilayer ZSM-5 membranes with spatially engineered acidity

To overcome water-induced deactivation in methanol-to-dimethyl ether (DME) conversion, bilayer ZSM-5 zeolite membranes were designed and prepared to improve the catalytic activity and water management. A siliceous high-Si/Al top layer and an aluminous low-Si/Al bottom layer were sequentially grown on a support, achieving a seamlessly intergrown ZSM-5 bilayer with no observable interfacial boundary. This architecture localizes active acid sites in the lower (high-Al) catalytic zone while a hydrophobic upper layer repels water and facilitates its removal. In methanol-to-DME catalytic membrane reactors, the bilayer membranes outperformed single-layer counterparts in water management and stability. The optimal bilayer (high-Si/Al top over low-Si/Al bottom) maintained a stable methanol conversion after 300 h on stream, whereas a conventional single-layer ZSM-5 membrane lost more than 80% of its activity in the same period. A reverse bilayer (low-Si/Al top over high-Si/Al bottom) exhibited higher initial conversion but suffered a ∼ 32% decline by 300 h, underscoring the importance of layer ordering. These results demonstrate that spatially distributing acidity and hydrophobicity within a zeolite membrane markedly improves water management and catalyst longevity. The bilayer design offers a promising strategy to extend the lifetime of catalytic membrane reactors for DME synthesis.