Synthesis and characterization of Co–Al–Fe nonstoichiometric spinel-type catalysts for catalytic CO oxidation

Abstract

A series of CoAlFe nonstoichiometric spinel-type oxides were synthesized from hydrotalcite precursors prepared through a co-precipitation method, and their catalytic activities for CO oxidation were investigated. The solids were characterized by XRD, BET, SEM, TG-DTG, H₂-TPR and in situ FTIR. The calcined hydrotalcite-like precursors were composed of spinel-like CoAlFe mixed oxide with crystallite sizes in the range 8–10.5 nm. The nanosized spinel oxide catalysts showed higher surface area as calcination led to dehydroxylation and carbonate decomposition of anions in interlayer spaces. FTIR results showed two vibrational frequency bands (ν1 and ν2) for tetrahedral and octahedral sites, confirming the formation of the Co₃O₄ spinel. Iron ions were introduced into the spinel system leading to improved redox properties, as confirmed by TPR. Furthermore, the CoAlFe ternary oxide nanoparticles exhibited superior catalytic performance in CO oxidation in contrast with CoAl and CoFe binary oxides, which can be ascribed to the improved reducibility. According to the in situ FT-IR analysis, CO adsorbed on the catalyst surface reacted with surface lattice oxygen to form CO₂. In addition, CO₂ could adsorb on the surface and form intermediate carbonate species.