CO₂-mediated selective cracking of n-butane to ethylene over HZSM-5-based catalysts

Catalytic cracking of light alkanes is one of the most important processes for the production of ethylene and propylene. However, how to effectively regulate the ethylene/propylene (E/P) ratio, especially achieving a ratio higher than 1 under mild conditions, remains a challenge. Herein, a series of HZSM-5-based (bare HZSM-5 and Pt/HZSM-5) catalysts were investigated in the reaction of n-butane catalytic cracking. The effects of Si/Al ratio, Pt loading, and CO₂ introduction on the catalytic performance of n-butane catalytic cracking, especially the formation of ethylene and propylene, were systematically studied. It is observed that the conversion of n-butane increased with the decrease in Si/Al ratio, and the presence of Pt contributes to the C − H bond activation in n-butane, thus promotes the n-butane conversion. The E/P ratio is also influenced by the Si/Al ratio and Pt introduction, but the ratio is not higher than 1. In contrast, the introduction of CO₂ component during n-butane catalytic cracking significantly increases the E/P ratio over different HZSM-5-based catalysts, and the highest ratio reaches 1.27. The increased E/P ratio is due to the enhancement of ethylene desorption in the presence of CO₂ based on C₂H₄-TPD and theoretical calculations, resulting in a faster desorption of ethylene and reduced possibility of side reactions. It is expected that the obtained knowledge of tuning the catalytic performance especially the formation of ethylene provides guidance for the practical industrial application under the background of higher demands for ethylene nowadays.