Lewis Acidic Zn/S-1 Zeolite Enables Direct Dehydrogenative Aromatization of Long-Chain Olefins

Aromatics, as essential chemical feedstocks, are predominantly derived from nonrenewable petroleum resources. With the rapid advancement of syngas–to–olefins (STO) technology, Fischer–Tropsch (F–T) olefin aromatization has emerged as a promising alternative route for aromatics production. Developing high-performance zeolite catalysts for the aromatization of long-chain olefins remains a significant challenge. In this study, a purely Lewis acidic catalyst, Zn/S-1, was synthesized by incorporating Zn into S-1 (Silicalite-1) zeolite via a dynamic gas-phase migration method. Under reaction conditions of 520 °C, 0.1 MPa, and a weight hourly space velocity (WHSV) of 0.2 h^–1, the catalyst achieved complete conversion of 1-octene with an aromatic selectivity of up to 77.1%. Comprehensive characterization using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM) revealed that the incorporation of Zn species into the S-1 framework leads to the consumption of silanol groups and the formation of uniformly dispersed (Zn–O_x)₂ dimeric active sites. Pyridine adsorption infrared spectroscopy further confirmed that these (Zn–O_x)₂ dimeric species impart exclusively Lewis acidity to the S-1 zeolite. Compared with conventional Brønsted acid-catalyzed pathways, which typically involve multiple steps such as C–C bond cleavage, oligomerization, and hydrogen transfer, the Lewis acid sites enable a more direct aromatization pathway via dehydrogenation. This distinct mechanism not only enhances aromatic yield but also suppresses the formation of low-value alkanes.