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 t hat many catalysts are active for the oxidation of soot, and that the contact between soot and catalyst is an important parameter for the ac tivity of the catalyst. In this study, the contact between soot and ca talyst is studied under practical conditions. Soot from a one-cylinder diesel engine is deposited either on catalyst material which is suppo rted by a sheet of filter paper, or on catalytic coatings on segments of wall-flow monolith. It is shown that under these practical conditio ns, the activity of the catalysts for oxidation of soot is low. Theref ore, it is concluded that under practical conditions the contact betwe en soot and catalyst is poor. It is shown that this contact resembles the contact denoted as 'loose contact' that had earlier been used in p art I of this study. This finding has major consequences for the use o f catalytic coatings for the removal of soot from diesel exhaust gases , because only when the contact between catalyst and soot can be incre ased, the use of catalytic coatings seems to be feasible.