Dip coating of ceria–manganese mixed oxides on cordierite and its CO oxidation activity

Dip coating method was utilized for wash-coating alumina onto cordierite honeycomb substrate, followed by catalyst coating by sol–gel dip coating of CMX(X = 0, 5, 70, and 100 corresponding to Ce_1-xMn_xO_2-δ, where x = 0, 0.5, 0.7, and 1) to obtain CM0/Al₂O₃/Cord, CM5/Al₂O₃/Cord, CM70/Al₂O₃/Cord, and CM100/Al₂O₃/Cord. The sol–gel was obtained from the EDTA–citrate method. XRD, BET, and BJH analysis was conducted on samples Cord to CM100/Al₂O₃/Cord. An intense peak of ceria at 462.53 cm⁻¹ and that of Mn₃O₄ was observed at 658 cm⁻¹ in the Raman spectra analysis. The adherence test was conducted to test the mechanical stability of the wash-coat and catalyst layer. The visual evidence of coating was furnished by optical imaging and FESEM analysis. Ultrafine particles with high porosity were observed in sample Al₂O₃/Cord. Cracks were observed in the FESEM images of CM0/Al₂O₃/Cord to CM100/Al₂O₃/Cord samples. CO oxidation studies were performed on the samples Cord to CM100/Al₂O₃/Cord. CM70/Al₂O₃/Cord performed the best among all other samples with a T₅₀ temperature of 157 °C. The activation energy of CO oxidation was calculated using the Ozawa method for samples CM0/Al₂O₃/Cord to CM100/Al₂O₃/Cord. 50 h long-term CO oxidation stability experiments were also conducted on samples CM0/Al₂O₃/Cord to CM100/Al₂O₃/Cord. The synergistic effects of ceria and manganese, combined with fine dispersion of the catalyst, pore characteristics, and cracks improving diffusivity, pitched CM70/Al₂O₃/Cord to have the best CO oxidation activity.