Direct synthesis of aromatics from carbon dioxide hydrogenation was investigated in a single stage reactor using hybrid catalysts composed of iron catalysts and HZSM‐5 zeolite. Carbon dioxide was first converted to CO by the reverse water gas shift reaction, followed by the hydrogenation of CO to hydrocarbons on iron catalyst, and finally the hydrocarbons were converted to aromatics in HZSM‐5. Under the operating conditions of 350°C, 2100 kPa, and CO2/H5 = 1/2, the maximum aromatic selectivity obtained was 22% with a CO2 conversion of 38% using fused iron catalyst combined with the zeolite. Together with the kinetic studies, thermodynamic analysis of the CO2 hydrogenation was also conducted. It was found that unlike Fischer Tropsch synthesis, the formation of hydrocarbons from CO2 may not be thermodynamically favored at higher temperatures.
Studies on the structural changes and catalytic behavior of iron‐manganese catalysts for CO hydrogenation were conducted using Mossbauer spectroscopy, X‐ray diffraction, temperature programmed reduction and kinetic measurements. It was observed that the reduction of the mixed oxide catalyst precursors proceeds via the formation of Fe3‐xMnxO4,Mn3‐xFexO4 mixed spinel and Fe1‐zMn2O mixed oxide to α‐iron and MnO. After use for CO hydrogenation, catalysts are oxidized as well as carburized. The Mn3‐yFeyO4 mixed spinel and Fe1‐2MnzO mixed oxide are the most powerful phases for olefin production. The highest attainable 2–4 low carbon olefin selectivity is 41% with an 86% conversion level. Higher manganese content or lower reduction temperatures may change the carbide formed from χ‐Fe5C2 to the more unstable ϵ′‐Fe22C. Carbide formation is greatly dependent on manganese content and activation procedure used.
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