The synergistic effect between ZnO and ZnCr2O4 on the catalytic performance for isobutanol synthesis from syngas

Abstract

The synergistic effect between ZnO and ZnCr2O4 has a notable beneficial effect on isobutanol synthesis from syngas over Zn-Cr based catalysts. A series of Zn-Cr catalysts with different nanoparticle sizes and varied contact probabilities of the two phases (ZnO and ZnCr2O4) were prepared by tuning the calcination temperature and preparation methods, aiming to reveal the nature of synergistic effect between the two active phases. The catalysts were characterized by XRD, HRTEM, in situ FT-IR, XPS, CO2-TPD, NH3-TPD. The catalytic evaluation results showed that the Zn1Cr1Ox catalyst, prepared by co-precipitation method and calcined at lower temperature of 400 °C, exhibited the highest total alcohol selectivity and isobutanol fraction (25% among total alcohols). As revealed by XRD and TEM results, compared to other catalysts, the Zn1Cr1Ox catalyst with the minimum particle size (4–5 nm) of the two phases exhibited tighter contact and stronger synergistic effect. Futhermore, the acid-base performance test proved that the intimate contact of the two phases boosted the quantity of acid and base sites, which was conducive to the activation of CO and the carbon chain growth to isobutanol. More importantly, the strong synergistic effect of two active phases enhanced the chance of removing hydroxyl groups, which provided a favorable role for the formation of C1 intermediates in the process of isobutanol synthesis.