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

## TL;DR

This study shows that adjusting the pH during the synthesis of K-OMS-2 improves its ability to oxidize soot at lower temperatures.

## Contribution

The paper introduces a kinetic perspective on how synthesis pH affects the catalytic performance of K-OMS-2 for soot oxidation.

## Key findings

- The pH5 sample showed higher crystallinity and better redox properties than the pH3 sample.
- The pH5 catalyst achieved a lower T50% of 368°C compared to 389°C for pH3 and 592°C for uncatalyzed soot.
- The pH5 sample had a lower activation energy (~130 kJ/mol) than the pH3 sample (~150 kJ/mol).

## Abstract

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
Oads/Olatt ratio of 0.86, indicating enhanced
redox behavior and oxygen mobility. TGA-based soot oxidation tests
showed that the pH5 catalyst achieved a T
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 (E
a = ∼130 kJ/mol) compared
with the pH3 sample (E
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.