Highly Dispersed CrOx Nanoparticle-Modified NaZSM-5 for Dehydration of Methanol to Dimethyl Ether

In this work, CrOx nanoparticle-and H+-modified NaZSM5 was prepared by impregnating in chromium nitrite aqueous solution to form Cr/HNaZSM-5 composites. They were characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet- visible (UV-vis), XPS, 29Si and 27Al MAS NMR, NH3-(CO2-) TPD, and N2 adsorption/desorption measurements, revealing that the Cr/ HNaZSM-5 composites possessed moderate surface acidity and basicity due to the Cr species or H+ partly substituting for the counter Na+ and highly dispersed CrOx nanoparticles on zeolites. The obtained composites thus provided promoting performance for catalyzing methanol dehydration to dimethyl ether with >90% conversion and ca. 100% selectivity at a lower reaction temperature. The promoted performance comes from acidic and basic sites for activating methanol to produce CH3+ and CH3O- intermediates, respectively. Moreover, as the catalyst works in succession over 500 h, the reactivity abatement is not found, suggesting excellent running stability.

Automated summary

CrOx nanoparticle-and H+-modified NaZSM5 composites were prepared and characterized. The composites showed moderate surface acidity and basicity, resulting from the substitution of Cr species or H+ for counter Na+ and the highly dispersed CrOx nanoparticles on zeolites. The composites exhibited excellent performance in catalyzing methanol dehydration to dimethyl ether, with over 90% conversion and nearly 100% selectivity at lower reaction temperature. The activity remained stable over 500 hours of continuous operation, indicating excellent running stability.