The promotion effects of alkaline earth metals on the properties of Cr/η-Al2O3 catalysts for propane dehydrogenation

Abstract

The Cr/Al₂O₃ catalyst, a prevalent system in commercial applications, plays a significant role in propane dehydrogenation (PDH). Notable improvements in this catalyst’s efficiency are essential for its continued use. In order to examine the effect of alkaline earth metals on the catalyst performances in the propane dehydrogenation reaction, a series of Cr/η-Al₂O₃ were synthesized by the impregnation method. The synthesized catalysts were designated as Cr-T/η-Al₂O₃, where T represents Ca, Mg, Sr, and Ba. The supports and the catalysts were studied using the following techniques: XRD, N₂ adsorption–desorption, temperature-programmed desorption and reduction, UV–Vis and Raman spectroscopy, and XPS analyses. The findings reveal that the Cr-Ba/η-Al₂O₃ catalyst exhibits better catalytic performance, with significantly higher propane conversion and propylene selectivity (with initial values of 66 % and 86.2 %, respectively) compared to other catalysts. The enhanced performance is attributed to the increased dispersion of Cr species, stabilization of Cr⁶⁺ species, and reducing the total amount of acid sites and strong acid sites, which are crucial for maintaining active sites and minimizing coke deposition. The Ba-modified catalyst also demonstrated excellent stability, with a lower deactivation rate (Ba(0.201 h⁻¹) < Sr(0.213 h⁻¹) < Ca(0.270 h⁻¹) < Mg(0.310 h⁻¹) < parent(0.338 h⁻¹)) and robust regenerative capacity over multiple cycles.