CO₂ hydrogenation to light olefins over Fe–Co/K–Al₂O₃ catalysts prepared via microwave calcination

Abstract

This study evaluates the effects of microwave calcination on Fe-Co/K-Al₂O₃ catalysts for CO₂ hydrogenation to light olefins, comparing microwave-treated samples at various power settings (700 W, 616 W, 511 W and 364 W) with a traditionally calcined counterpart. The lowest power setting results in incomplete precursor decomposition, adversely affecting Fe, K, and Al₂O₃ interactions. At medium power, though decomposition improves, Fe₂O₃ aggregates due to poor dispersion. Medium-high power produces rod-shaped structures with enhanced Fe and K contact, while the highest setting increases Fe₂O₃ particle size and Fe-K species content to 35.4%, still below the 37.9% observed in the traditional catalyst. Significantly, the formation of Fe-C species (Fe₅C₂) correlates positively with Fe-K interactions, enhancing the olefins to paraffins ratio. Additionally, the role of Fe₃O₄ is vital, providing the highest light olefins yield (24.5%) at an optimal Fe-C/Fe₃O₄ ratio of 0.34 in the medium-high power sample. Compared to the traditional catalyst, which declines significantly in CO₂ conversion and olefin yield due to carbonaceous deposits over time, the medium-high power catalyst shows stable performance and reduced coke formation. Moreover, microwave calcination slashes energy consumption by over 99%, underscoring its potential for more sustainable and efficient catalyst preparation.