Catalysts for the oxidation of soot from diesel exhaust gases .2. Contact between soot and catalyst under practical conditions

In part I of this study [Appl. Catal. B 8 (1996) 57-78] it was shown that many catalysts are active for the oxidation of soot, and that the contact between soot and catalyst is an important parameter for the activity of the catalyst. In this study, the contact between soot and catalyst is studied under practical conditions. Soot from a one-cylinder diesel engine is deposited either on catalyst material which is supported by a sheet of filter paper, or on catalytic coatings on segments of wall-flow monolith. It is shown that under these practical conditions, the activity of the catalysts for oxidation of soot is low. Therefore, it is concluded that under practical conditions the contact between soot and catalyst is poor. It is shown that this contact resembles the contact denoted as 'loose contact' that had earlier been used in part I of this study. This finding has major consequences for the use of catalytic coatings for the removal of soot from diesel exhaust gases, because only when the contact between catalyst and soot can be increased, the use of catalytic coatings seems to be feasible.