Influential Role of Elemental Migration in a Composite Iron-Zeolite Catalyst for the Synthesis of Aromatics from Syngas

A composite catalyst of a metal oxide and a zeolite has been widely adopted for the direct conversion of syngas to aromatics (STAs). However, its stability along with higher conversion and selectivity remains a bigger challenge to overcome. Herein, we present an efficient STA catalyst composed of a Na-modified Fe-Mn oxide and an HZSM-5 zeolite; however, a gradual decline was observed in the aromatization activity of the zeolite, which was significantly ascribed to the influence of elemental migration from the Fe-based catalyst to the zeolite. Further investigation revealed that the migrated metal oxides could block pore channels; meanwhile, abundant Na diminished Lewis acid sites by donating electrons to the zeolite during the reaction, which adversely affected the catalytic performance. Therefore, on synthesizing a well-designed catalyst in optimized promoter contents and integrating it with high-acidity nano-HZSM-5 in proper proximity, a higher CO conversion greater than 95% and an overall aromatic selectivity exceeding 53% were achieved with extended stability of 120 h. This work reveals a particular dimension for the microscopic interaction between the metal oxide and the zeolite in the composite catalyst, providing a promising perception of catalyst design for the synthesis of aromatics from syngas.