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A study of the impact of the exhaust environment and catalyst composition on the performance of direct soot oxidation catalysts has been performed. In agreement with previous studies it is noted that contact efficiency between soot and catalyst dictates soot oxidation rate, with tight contact required for low temperature soot oxidation. However it is shown that contact efficiency is not a static feature and under application conditions a ‘De-Coupling’ of intimately mixed catalyst and soot can occur in-situ, resulting in loss of contact efficiency and activity. The mechanism of ‘De-coupling’ has been investigated and demonstrated to arise from the ubiquitous NO2-mediated soot oxidation mechanism. It is proposed that incomplete filter regeneration by NO2 dictates the requirement for active filter regeneration due to retention of residual soot, physically ‘distant’ from the washcoat.