High Stability of Methanol to Aromatic Conversion over Bimetallic Ca,Ga-Modified ZSM‑5

The production of
valuable aromatics and the rapid catalyst deactivation
due to coking are intimately related in the zeolite-catalyzed aromatization
reactions. Here, we demonstrate that these two processes can be decoupled
by promoting the Ga/HZSM-5 aromatization catalyst with Ca. The resulting
bimetallic catalysts combine high selectivity to light aromatics with
extended catalyst lifetime in the methanol-to-aromatics process. Evaluation
of the catalytic performance combined with detailed catalyst characterization
suggests that the added Ca interacts with the Ga-LAS, with a strong
effect on the aromatization processes. A genetic algorithm approach
complemented by ab initio thermodynamic analysis is used to elucidate
the possible structures of bimetallic extraframework species formed
under reaction conditions. The promotion effect of minute amounts
of Ca is attributed to the stabilization of the intra-zeolite extraframework
gallium oxide clusters with moderated dehydrogenation activity.