Impact of soot loading on CO oxidation in catalytic particulate filters with various coating structures

The relationship between the amount of soot deposited in ceramic monolith filters with different catalytic coating structures and the resulting conversion of gaseous pollutants is examined using catalytic CO oxidation as the test reaction. Two types of catalytic filter samples were prepared by applying controlled on-wall or in-wall coatings of a model Pt/γ–Al₂O₃ catalyst on a cordierite monolith filter. Each sample was studied as clean, with soot at five progressively increasing loadings, and after regeneration. CO light-off curves were measured for each state of the catalytic filter at mild and high gas space velocities, with a focus on the light-off temperature and conversion under mass-transfer-limited conditions. The results indicate that the deposited soot does not affect the CO oxidation onset but leads to increasing CO slip in diffusion-limited regime, particularly at high flow rates. The observed CO slip increases non-linearly with soot loading, showing the highest sensitivity at lower soot levels and leveling off at higher soot deposits.