Unraveling the Intrinsic Reasons Promoting the Reactivity of ZnAl2O4 Spinel by Fe and Co for CO Oxidation

To develop active and stable catalysts for CO oxidation at relatively higher temperature region for exhaust treatment, ZnAl2O4 spinel promoted by Fe and Co have been fabricated and characterized by different means. While Fe doping improves only slightly the activity, Co doping increases the activity remarkably. XRD and Raman results have proved that ZnAl2O4 spinel is the major phase for all the samples. By Fe doping, a new ZnFe2O4 spinel compound is formed. By Co doping, two new ZnCo2O4 and CoAl2O4 spinels are generated, which can provide both surface Co3+ and Co2+ sites for effective CO adsorption. XPS and EPR have testified that surface superoxide O-2(-) anion is the major active oxygen sites for the reaction. It is disclosed that the concerted interaction between surface O-2(-) species and CO adsorption sites determines the activity. Compared with the un-modified Zn-Al spinel sample, Fe doping improves slightly the amount of active oxygen species, but decreases the amount of CO adsorption sites. However, Co doping increases the amount of both kinds of sites evidently due to the formation of ZnCo2O4 and CoAl2O4 spinels. As a consequence, Zn-Co-Al exhibits the optimal activity in all the catalysts.

Automated summary

This study demonstrates that doping Fe and Co can significantly enhance the CO oxidation activity of ZnAl2O4 spinel, with Co doping showing more remarkable effect. Doping with Fe and Co respectively forms new compounds, while Co doping generates more active sites by producing new spinels.