The catalytic effect of chromium-doped ceria-praseodymium on soot oxidation activity and its kinetics

Soot generated from the partial combustion of diesel significantly contributes to air pollution, and catalytic oxidation is currently an effective method for removing diesel soot particles. The chromium-doped ceria-praseodymium (Cr-CP) catalyst system is synthesized via solution combustion synthesis and evaluated for soot oxidation activity, with a subsequent kinetics study conducted. The XRD analysis of the catalysts indicated a decrease in crystallite size and increased lattice strain and reactive facet ratios for all Cr-doped CP samples. Raman analysis verified the existence of oxygen vacancy peaks in all chromium-doped CP catalysts. X-ray photoelectron spectroscopy (XPS) revealed the presence of adsorbed H₂O or molecular water peaks in the O1s spectra for the 5 Cr-CP catalyst, which also exhibited a high concentration of surface Cr³⁺ ions. Thermogravimetric analysis (TGA) of soot oxidation indicated that 5 Cr-CP exhibited a superior T₅₀ of 393 ± 2 °C, mostly attributed to the presence of reducible surface Cr³⁺ ion species. Kinetic analysis was performed on all Cr-doped CP catalysts to assess the kinetic triplets: activation energy, pre-exponential factor, and reaction model. The activation energy was low (87 kJ mol^-1, Ozawa method) for 15 Cr-CP, while the pre-exponential factor was higher for 5 Cr-CP (7.39 × 10¹⁰ min^-1). The Cr-CP catalyst system adhered to a power law, indicating a phase boundary-controlled reaction characterized by nucleation and growth mechanisms. The consistency between experimental and calculated curves confirmed that the developed catalysts adhered to the Avrami-Erofeev equation (Am) or the nucleation and growth model.