Conversion of Isobutanol to Olefins and Aromatics over HZSM-5-Based Catalysts: Tuning of Product Selectivity

Isobutanol derived from biomass can serve as a potential renewable candidate for the production of light olefins and aromatics, which are the building blocks to manufacture fuels and chemicals in the petrochemical industry. Dependent upon the product requirements, the product selectivity toward olefins or aromatics can be tuned by adjusting the reaction conditions and the properties of HZSM-5 catalysts. On bare HZSM-5, mild conditions (low temperature, low space time, and low acidity) favored the production of olefins and harsh conditions (high temperature, high space time, and high acidity) were more likely to produce aromatics. Ga was impregnated onto HZSM-5 to enhance the production of aromatics. Unexpectedly, Ga introduction only induced the intertransformation between olefins and aromatics without significantly impacting the selectivity of low-value paraffins. The exchanged Ga sites functioning together with Brønsted acid were identified as active Ga species and strengthened the direct dehydrogenation of C6–C8 olefins. The in situ-generated water from isobutanol dehydration affected the formation of Ga species. This resulted in different promotional effects of Ga on the transformation of isobutanol and isobutene. The reaction pathways were developed on the basis of the catalyst evaluation results, in tandem with an in situ diffuse reflectance infrared Fourier transform spectroscopy study on the intermediates formed during isobutanol transformation. Selectivity of olefins and aromatics from isobutanol transformation can be tuned by adjusting reaction conditions and properties of HZSM-5 catalysts.