Stable and efficient aromatic yield from methanol over alkali treated hierarchical Zn-containing HZSM-5 zeolites

• Hierarchical Zn/HZSM-5 (H-Zn/HZSM-5) was prepared by treating in-situ synthesized Zn/HZSM-5 with NaOH solution.
• High BET specific surface area of 551 m2/g and suitable amount of acid sites was retained on H-Zn/HZSM-5.
• H-Zn/HZSM-5 exhibited initial space time yield of 0.62 g gcat−1 h−1 and the lifetime of 120 h.
• The high coke capacity up to 24.3% was observed on the spent H-Zn/HZSM-5.

Fast deactivation of catalyst is the main problem in methanol-to-aromatics (MTA) process. Herein, Zn-containing HZSM-5 zeolites with hierarchical pores (H-Zn/HZSM-5) were prepared by treating directly synthesized Zn/HZSM-5 with NaOH solution. The changes in crystallinity, acidity and textural properties of Zn/HZSM-5 before and after alkali treatment were characterized by X-ray diffraction, NH3-TPD, 27Al MAS-NMR, N2 physisorption, X-ray fluorescence and TEM techniques. MTA reaction under the operating conditions of T = 400 °C and WHSV = 2.5 h−1 showed that the aromatic yield was improved from 41.4% for HZSM-5 to 55.3%. Furthermore, H-Zn/HZSM-5 exhibited a high initial space time yield of 0.62 g gcat−1 h−1 and a long lifetime up to 120 h. These results could be ascribed to the hierarchical pores and the providential acidity, which enhanced the adsorption and diffusion of intermediates/products during the reaction.

Combination of Zn/HZSM-5 prepared by direct synthesis and enhanced diffusion properties resulting from mesopores provides an effective way to improve the catalyst life and aromatic yield from methanol under high WHSVs. Compared with the aromatic yield of 41.4% and the lifetime of 40 h for the conventional HZSM-5, that of hierarchical Zn/HZSM-5 (H-Zn/HZSM-5) exhibited 55.3% and 120 h, respectively, under conditions of T = 400 °C and WHSV = 2.5 h−1.Figure optionsDownload as PowerPoint slide