Catalyst Design for Efficient Olefin Aromatization: Insights into Metal-Promoted ZSM-5 Catalysts for Light and Heavy Olefin Conversion

Abstract

Olefin aromatization is a critical industrial process to produce high-value aromatic hydrocarbons, which are essential for making commodity and fine chemicals, pharmaceuticals, polymers, dyes, and jet fuel-range hydrocarbons. When the olefins are derived from renewable or waste-based sources, the resulting aromatics (C₈–C₁₆) can contribute to sustainable aviation fuels (SAF). Traditionally, metal-promoted zeolites, especially ZSM-5, have been used as catalysts wherein aromatics are formed inside the zeolite cages, and the presence of metal promoters facilitates the overall reaction and enhances the yield of aromatics. Understanding the specific role of metal promoters in the aromatization of light olefins (i.e., ethylene and propylene) and larger olefins (i.e., C₄₊ olefins) is important for sustainable catalyst design. Various state-of-the-art characterization techniques, such as solid-state NMR, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), have been used extensively to provide insights into the role of different types of metal species, i.e., their influence on the acidic properties of the catalyst and their effect on zeolite structure changes during aromatization reactions. Advanced synthetic methodologies were used to control the content of active species, the structure, and acidic properties of zeolites. It has been found that metal cations in the framework of zeolites are key active species that promote aromatization activity, while surface-oxidized metal species can act as dehydrogenation sites for olefins. While the aromatization of light olefins such as ethylene and propylene has been studied extensively, challenges remain with mixed olefin aromatization, especially considering the reactivity of larger olefins (C₄₊ olefins) is markedly different due to the presence of alkyl chains. This Perspective intends to highlight and address these challenges as various emerging technologies produce mixed olefin from renewable feedstocks. Thus, the rational development of catalysts and catalytic processs toward mixed olefin aromatization will have increasing importance and will pave the way toward sustainability.