Enhanced CrOx Catalyst Performance in Propane Dehydrogenation: Unveiling the Effect of Bi-Modified Alumina Support

Propane dehydrogenation (PDH) over chromium-based catalysts is often limited by rapid deactivation and poorly controlled surface acidity. Here, Bi-promoted CrOx/η-Al2O3 catalysts (0.75–6 wt% Bi) were developed to regulate the redox and acidic properties of chromium sites. Bi incorporation significantly modified Cr dispersion and surface acidity, thereby improving catalytic performance. Catalytic testing at 580 °C and 1 atm revealed that intermediate Bi loadings provided the most favorable results, with Cr/1.5Bi-Al2O3 and Cr/3Bi-Al2O3 exhibiting favorable propylene yields and selectivities compared with the unmodified and commercial reference catalysts under the investigated reaction conditions. The Cr/3Bi-Al2O3 catalyst achieved a propylene yield of 48.9% with 93.3% selectivity, while Cr/1.5Bi-Al2O3 reached 47.17% yield with 93.6% selectivity, and both catalysts exhibited the lowest coke deposition. Notably, the optimized Cr/3Bi-Al2O3 catalyst showed a modified distribution of chromium oxide species and a favorable Cr6+/Cr3+ ratio of 2.40, which contributed to improved redox behavior and suppression of strong acid sites responsible for cracking and coke formation. These results demonstrate that controlled Bi promotion effectively tunes the redox–acidic balance of Cr catalysts, thereby improving stability and propylene production during PDH.