High-Impact Promotional Effect of Mo Impregnation on Aluminum-Rich and Alkali-Treated Hierarchical Zeolite Catalysts on Methanol Aromatization

Abstract

A systematic change of HZSM-5 (HZ5) as a catalyst of the methanol to aromatics (MTA) reaction was undertaken by employing a fixed-bed tubular-type reactor under ambient pressure, applying a weight hourly space velocity (WHSV) of 2 h–1 at 375 °C, as the first report on the application of low-Si/Al-ratio alkaline-[Mo,Na]-HZSM-5 in the MTA process. To characterize the surface and textural properties of the catalysts, powder X-ray diffraction (PXRD), nitrogen adsorption/desorption, temperature-programmed desorption of ammonia (NH3-TPD), pyridine-infrared spectroscopy (Py-IR), thermogravimetric analysis (TGA), and energy-dispersive X-ray (EDX) methods were employed. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) measurements demonstrated a selectivity of up to 86 wt % (65.7 wt % for benzene, toluene, and xylene (BTX)) over 2[Mo]­HZ5. NH3-TPD and Py-IR results indicated a sensible decrease of strong acid sites on the impregnated samples, while the surface analyses revealed the highest Lewis acid sites (LAS) together with the largest mesopore surface area for 2[Mo]­alk-HZ5, supporting the migration of Mo species to the bulk of the catalysts. Mo impregnation had a minor effect on the observed coke formation in the promoted catalyst.

Influence of Mo modification on coaromatization coupling methanol with n-hexane over [Zn,Mo]/HZSM-5 catalysts

“…Many Mo species covering the BASs resulted in insufficient BASs to promote the polymerization and cyclization of small molecule olefins, which in turn led to an increase in the selectivity to small molecule olefins and a decrease of aromatics. 26,27 3.5.2 Effect of reaction temperature. The conversion of methanol was kept at 100% at different reaction temperatures.…”

“…MoO 3 is an effective promoter in methane aromatization through activating the C-H bonds of methane molecules. 25,26 It has been reported that Mo modification promoted the oligomerization and aromatization to improve the yield of aromatics. 27 At present, there are still no reports about the modification of HZSM-5 with Zn and Mo for the coaromatization reaction coupling methanol with n-hexane.…”