Low-Temperature CO Oxidation over Combustion Made Fe- and Cr-Doped Co₃O₄ Catalysts: Role of Dopant’s Nature toward Achieving Superior Catalytic Activity and Stability

Abstract

Co3O4 with a spinel structure shows unique activity for CO oxidation at low temperature under dry conditions; however the active surface is not very stable. In this study, two series of Fe- and Cr-doped Co3O4 catalysts were prepared by a single-step solution combustion technique. Fe was chosen because of its redox activity corresponding to the Fe2+/Fe3+ redox couple and compared to Cr, which is mainly stable in the Cr3+ state. The catalytic activity of new materials for low-temperature CO oxidation was correlated to the nature of the dopant. As a function of dopant concentration, the temperature corresponding to the 50% CO conversion (T 50) demonstrated significant differences. The maximal activity was achieved for 15% Fe-doped Co3O4 with T 50 of −85 °C and remained almost constant up to 25% Fe. In the case of Cr, the activity was observed to be maximum for 7% of Cr with T 50 of −42 °C and significantly decreased for higher Cr loadings. Similarly, there was a contrasting behavior in catalyst stability too. 100% CO conversion was achieved below −60 °C for 15% Fe/Co3O4 catalyst and remained unchanged even after calcination at 600 °C. In contrast, Co3O4 or 15% Cr/Co3O4 catalysts strongly deactivated after the same treatment. These differences were correlated to the oxidation states, coordination numbers, the nature of surface planes, and the redox properties. We observed that both Cr and Fe were typically present in the +3 oxidation state, occupying octahedral sites in the spinel structure. The catalysts were mainly exposed to (111) and (220) planes on the surface. H2-TPR indicated clear differences in the redox activity of materials due to Fe and Cr substitutions. The reducibility of surface Co3+ species remained similar in all Fe-doped Co3O4 catalysts in contrast to nonreducible Cr-doped analogs, which shifted the reduction temperature to the higher values. As the Fe3+/Fe2+ redox couple partly substituted the Co3+/Co2+ redox couple in the spinel structure, similar bond strength of Fe–O keep redox activity of Co3+ species almost unchanged leading to higher activity and stability of Fe/Co3O4 catalysts for low-temperature CO oxidation. In contrast, nonreducible Cr3+ species characterized by strong Cr–O bond substituting active Co3+ sites can make the Cr/Co3O4 surface less active for CO oxidation.

Synthesis of iron and vanadium co‐doped mesoporous cobalt oxide: An efficient and robust catalysts for electrochemical water oxidation

“…The HR-TEM image of the FeV-a/meso-Co hybrid (Figures 3C-E) showed smaller particles than its corresponding meso-Co, credited to Fe, and V coordinated with Co-cations in decreasing Co 3 O 4 particle size. 65 Figure 3F displays the lattice distance in the HR-TEM photographs agrees with the (311) interplanar distance of the Co 3 O 4 , further proving that the assynthesized FeV-a/meso-Co 3 O 4 sample is well crystallized.…”

Effect of Bi-functional Hierarchical Flower-like CoS Nanostructure on its Interfacial Charge Transport Kinetics, Magnetic and Electrochemical Behaviors for Supercapacitor and DSSC Applications

“…The two main peaks at 778.77 eV and 794.06 eV correspond to Co-2p 3/2 and Co 2p 1/2 . The binding energy separation between Co-2p 1/2 and Co-2p 3/2 was found to be 15.29 eV, which is in good agreement with reported values 30 . The main and shake up peaks appeared at high binding energies of 778.77 eV and 782.15 eV respectively is attributed to the presence of Co 2+ which affirmed with reported values 11,17 .…”

“…Figure 5 shows the high resolution XPS core level spectra of Co-2p and S-2p. The spin-orbital splitting of Co-2p peaks are deconvoluted into two main peaks, two low intense peaks with associated satellite peaks 30 (Fig. 5a).…”

Comparison of Different Metal Doping Effects on Co3O4 Catalysts for the Total Oxidation of Toluene and Propane

“…The doping of In 2 O 3 induced the structural distortion of Co 3 O 4 and promoted the catalytic performance of Co 3 O 4 for CO oxidation [13]. Baidya et al demonstrated that 15% Fe-doped Co 3 O 4 can achieve superior catalytic activity and stability towards CO oxidation [14].…”