Efficient Bifunctional Catalysts for Enhanced Carbon Conversions and Alky-Aromatics Production in Crude Bio-glycerol Methanol Processes

The present study reports the development of an alkali earth metal (Ba)-modified Zn/ZSM-5 catalyst for efficient carbon conversion of bio-derived crude glycerol toward aromatics production in a methanol (GMTA) co-process. The metal functionality caused considerable alteration in acidity to improve the dehydrogenation properties of the catalyst to produce more aromatics and to simultaneously control the undesired cracking reactions responsible for the gas product formation. The methanol concentration in the feed mixture was also observed to influence the carbon conversions toward liquid and gas products, especially aromatics. At optimized reaction conditions, the 0.1Ba-1Zn/ZSM-5 catalyst produced 69C% high-value gasoline blending stock possessing ∼57C% aromatics and ∼116 research octane number suitable for fuel applications. The aromatics formation was accompanied by 28 mol % of H2 as a valuable byproduct. XRD, FT-IR, and 27Al-NMR studies confirmed the structural integrity of ZSM-5 even after metal loading treatments. XPS and UV–Vis DRS spectra confirmed the presence of Zn in the form of (ZnOH)+ species. NH3-TPD and pyridine-IR studies revealed a decrease in the strong acidity of ZSM-5 along with a simultaneous increase in Lewis acidity. Thus, the enhanced carbon conversion and aromatics yield in the GMTA process observed on 0.1Ba-1Zn/ZSM-5 might be understood by two main factors, namely, (i) decreased strong Bronsted acid sites to suppress undesirable cracking reactions and (ii) increased Lewis acid sites to promote dehydrogenation reactions.