Influence of Preparation pH for Superior Soot Oxidation: A Kinetic Perspective of K-OMS-2

K-OMS-2, a tunnel-structured manganese oxide, has gained significant attention as a catalyst for soot oxidation due to its high redox capability and oxygen mobility. This study investigates the influence of the synthesis pH on the physicochemical properties of cryptomelane and its catalytic activity in soot oxidation. Two samples, synthesized at pH 3 and pH 5, were characterized using XRD, SEM, TEM, H₂-TPR, and XPS. The pH5 sample exhibited higher crystallinity, an increased Mn³⁺/Mn⁴⁺ ratio of 0.41, and a greater O_ads/O_latt ratio of 0.86, indicating enhanced redox behavior and oxygen mobility. TGA-based soot oxidation tests showed that the pH5 catalyst achieved a <i>T</i> _50% of 368 °C, compared to 389 °C for pH3 and 592 °C for uncatalyzed soot, indicating superior low-temperature activity. Kinetic analysis using Flynn-Wall-Ozawa (FWO) and Coats-Redfern (CR) models revealed a lower apparent activation energy for the pH5 sample (<i>E</i> _a = ∼130 kJ/mol) compared with the pH3 sample (<i>E</i> _a = ∼150 kJ/mol). These results confirm that synthesis pH significantly influences the structural and redox properties of cryptomelane and that catalysts with higher surface oxygen species and improved oxygen vacancy density exhibit enhanced catalytic performance.