Effect of unimodal and bimodal MCM-41 mesoporous silica supports on activity of Fe–Cu catalysts for CO2 hydrogenation

• Bimodal MCM-41 silica support was successfully synthesized by using TEOS (T).
• Fe–Cu loaded on unimodal and bimodal supports were tested for CO2 hydrogenation.
• The existence of larger mesopore could greatly improve the catalytic performance.
• 3Fe–10Cu/MCM-41 (T) was highly active and selective to alcohols at low temperature.

CO2 hydrogenation has been recognized as one of the most effective and economical ways to convert excess CO2 to valuable chemicals and/or fuels. In this research, CO2 hydrogenation to alcohols was carried out over Cu-based MCM-41 catalyst. The effects of pore characteristics of supports including unimodal and bimodal pore structures, loading amount of Fe, and reaction temperature on the catalytic performance were investigated. The bimodal MCM-41 (T) support revealed a short-range hexagonal pore structure with two different pore sizes, where the larger pore size was 30.5 nm and the smaller pore (2.7 nm) was equal to that of the unimodal MCM-41 (SS). Accordingly, Fe (0, 0.5, and 3 wt.%) and Cu (10 wt.%) loaded on bimodal MCM-41 (T) support was tested for CO2 hydrogenation and compared to that of MCM-41 (SS) support. The result showed that the activities of CO2 hydrogenation over xFe–10Cu/MCM-41 (T) catalysts were higher than xFe–10Cu/MCM-41 (SS) catalysts. Moreover, the addition of 3 wt.% Fe on 10Cu/MCM-41 (T) catalyst exhibited the highest CO2 conversion of 20.8% at the reaction temperature of 350 °C and the highest alcohol selectivity of 80–99% at low reaction temperature (160–200 °C). Furthermore, the highest TOF of alcohols and CO (1.08 × 10−25 and 5.47 × 10−25 mol surface metal atom−1 min−1) were also obtained over 3Fe–10Cu/MCM-41 (T) catalyst due to the high active Cu and Fe atoms on bimodal MCM-41 (T). These outstanding catalytic activities could be attributed to the pore characteristics of the supports. The existence of larger mesopore could greatly improve the catalytic performance as it led to the formation of metals with larger sizes, resulting in less metal–support interaction of which more favorable in this reaction.