CO2-enhanced alkane aromatization over Cu-ZSM-5 zeolite: Insights into active sites and catalytic performance

Abstract

Aromatization of alkanes represents an important process in the chemical industry, traditionally relying on noble metal catalysts. Developing a non-noble metal catalyst and a relevant new process offers significant potential for promoting technologic progress in this field. Herein, we present Cu-ZSM-5 zeolite as a highly effective catalyst for alkane aromatization, achieving outstanding aromatics selectivity. In-situ Fourier transform infrared spectra of adsorbed nitric oxide, high-angle annular dark field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electron paramagnetic resonance analyses reveal that the Cu²⁺ species act as the primary active centers for aromatics formation. During aromatization of alkanes, the reduction of Cu²⁺ to Cu⁺ species correlates with diminished aromatics selectivity. Notably, introducing CO₂ into the reaction feed not only enhances aromatics selectivity by maintaining Cu²⁺ species in their active oxidation state under reducing conditions, but also improves catalytic stability by eliminating coke. Furthermore, CO₂ is converted into CO and aromatic products during the reaction, offering a novel way for CO₂ utilization through the coupling reaction of alkane and CO₂.