Insights into the Key Factor of Zeolite Morphology on the Selective Conversion of Syngas to Light Aromatics over a Cr₂O₃/ZSM‑5 Catalyst

One-step conversion of syngas to aromatics (STA) over an oxide–zeolite bifunctional catalyst is promising as an alternative route for aromatic production. Control of aromatic distribution and enhancement of benzene, toluene, and xylene (BTX) selectivity are still a big challenge. Decoupling the complex reaction network, the relative activity of aromatization and alkylation on ZSM-5 determines the aromatic distribution. Herein, the STA reaction was studied over Cr₂O₃/ZSM-5 to reveal the influence of the zeolite morphology parameters on aromatic distribution. Using the “substitution ratio of aromatic ring” S_C9+/A to reflect the relative rate of alkylation to aromatization, the linear dependence of S_C9+/A on the morphology parameter (1/b) of ZSM-5 was revealed. The methodology for control of aromatic distribution by altering the crystal size of ZSM-5 along the b-axis is then proposed. By further enhancing the aromatization activity via ion exchange of Zn to ZSM-5, a bifunctional catalyst showing a high BTX space time yield of 2.47 mmol g^–1 h^–1 (on carbon base) with 49.1% BTX fraction is developed.