Experimental and theoretical studies on formaldehyde catalytic combustion over Cu–Fe spinel-type catalyst

Abstract

A series of Cu–Fe spinel-type catalysts were synthesized by sol–gel auto-combustion method for the catalytic combustion of HCHO. A combined experimental and theoretical investigation based on in situ FT-IR and density functional theory (DFT) was performed to uncover the reaction process of HCHO catalytic combustion on Cu–Fe spinel-type catalysts. The results show that CuxFe(3-x)O4 catalysts display the typical pattern of spinel structure. The chemical states of Cu and Fe cations on the catalyst surface include Cu+, Cu2+, Fe2+ and Fe3+. Cu0.5Fe2.5O4 exhibits excellent HCHO oxidation efficiency and good water-resistance performance. The superior catalytic performance of Cu0.5Fe2.5O4 catalyst is closely associated with the high crystalline degree of spinel. The flexible valences of metal cations in spinel-type catalysts are beneficial for electron transfer, thus facilitates HCHO adsorption and oxidation. Formate species (HCO2) is the major reaction intermediate during HCHO combustion. The reaction pathway of HCHO catalytic combustion contains eight elementary steps: HCHO adsorption, H2CO2 dehydrogenation, HCO2 dehydrogenation, CO2 desorption, O2 adsorption, OOH formation, H2O formation and desorption. HCO2 dehydrogenation is identified as the rate-determining step because of the highest energy barrier of 254.80 kJ/mol.