The performance of CO hydrogenation to olefins via the Fischer–Tropsch reaction (FTO) over iron catalysts depends greatly on the carrier. In this work, Mg/Al composite oxides were presented with different Mg/Al ratios. The structure, morphology, specific surface area, pore size, and alkalinity of the catalysts were characterized, and the active Fe species was found to be highly dispersed. Moreover, MgO could modify the catalyst alkalinity, with the medium and strong strengths reaching a climax at 60% MgO content, while the strong alkalinity increased monotonously with increasing MgO. Notably, increasing basic sites improved the CO conversion, but excessively strong basicity shifted the product to long-chain hydrocarbons and more alkanes. It was further found that MgO addition greatly promoted light hydrocarbons and the olefin/paraffin (O/P) ratio, with the maximum for C2 and C3 on pure MgO and C4 and C5 on 50% MgO·Al2O3. The catalyst with 50% MgO·Al2O3 support is recommended as the optimal one, with the olefins more than 60% in the hydrocarbon product, half among which are the light ones with the O/P ratios of 1.4, 6.7, 13.7, and 11.1 for C2–C5, respectively.

In the process of CO hydrogenation to olefins by the Fischer–Tropsch synthesis, the support is a key factor in the activity, selectivity, and thermal and chemical stability of the catalysts, and magnesium aluminate spinel has recently been reported to be very effective.

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