The methanol-to-aromatics (MTA) process is regarded as a promising route to produce aromatic commodities through non-petroleum carbon resources, such as biomass, waste, coal, natural gas, and CO2. In contrast with the industrially implemented methanol-to-olefin (MTO) process, most MTA studies are still in the laboratory-scale stage. Recently, a few demonstration plants of MTA have been successfully launched, indicating the importance and the gradual industrial maturity of this technology. However, there are still many fundamental questions and technological challenges that must be addressed. In this Review, we summarize the recent advances in mechanistic understanding on the reaction and catalyst deactivation during MTA, elaborate the available strategies to improve the catalytic performance, and correlate MTA studies with other important catalytic aromatization processes. With this knowledge in hand, we share our views on future research directions in this field.

The nucleation/crystallization processes to form nanoscale ZSM-5 crystals having aluminum zoning were studied by means of high-resolution transmission electron microscopy. Amorphous particles with a size between 40 and 80 nm are formed at the initial stage of zeolite growth, and such particles generally have an aluminum-rich edge. Intermediate crystals with an amorphous-core/crystalline-shell structure develop shortly after that, which indicates that nucleation preferentially takes place in the particle rim. Subsequently, rapid crystal lattice propagation toward the core gives rise to particles with a fully crystalline structure. The high aluminum content in the particle rim appears to be the driving force of the zeolite ZSM-5 nucleation and growth.

The aluminum migration toward the surface and the delayed addition of high-aluminum-containing species contribute to the aluminum-zoning of ZSM-5 zeolites.