* Corresponding author. Tel.: #39-11-5644654; fax: #39-11- 5644699. E-mail address: saracco@polito.it (G. Saracco). Chemical Engineering Science 56 (2001) 1613}1621 Combining "ltration and catalytic combustion in particulate traps for diesel exhaust treatment Michele Ambrogio, Guido Saracco*, Vito Specchia Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy Abstract Satisfying performance in Diesel soot abatement can be achieved by coupling ceramic-foam "lters with carbon combustion catalysts. This paper focuses on the preparation, testing and the modelling of such reactors. A speci"c pilot plant, based on a conical #uidised bed of glass beads, used to disperse "xedparcelsofDieselsootintoagivengas #owrate,wasusedtoassessthepressuredrop and the "ltration e$ciency of the foam traps as a function of the soot particle size, the soot load in the "lter, as well as the super"cial velocity. Then, several catalysts have been deposited into di!erent traps, whose abatement performance was evaluated in a speci"c pilot plant where an acetylene burner was used to produce a soot-laden #ue gas. High abatement e$ciency ('80%), coupled with low-pressure drop across the trap (100 mmH  O), has been obtained by using a catalyst based on Cs  V  O  . A mathematical model is presented and validated using the experimental data obtained with catalytic and non-catalytic traps. The model agreement with the experimental data was good in both cases and particularly promising for design purposes.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Diesel particulate; Catalytic combustion; Filtration; Ceramic-foam trap; Modelling 1. Introduction The higher and higher penetration of Diesel engines in the passenger-car market is due chie#y to their high e$ciency (close to 30% for the last generation, direct- injection, common-rail engines), and to their low fuel cost. Their continuously growing market-share has brought several environmental e!ects. It has been ob- served how diesel engines are responsible for small car- bonaceous particles and NO  emissions. Diesel particulate raises a special concern owing to its suspected cancer initiation activity. US, Japanese and European governments are therefore tightening their particulate emission limits for passenger, light- and heavy-duty vehicles equipped with diesel engines, so as to lower its concentration in the atmosphere of urban areas. Particularly, 2005 US and European standards will im- pose a serious technological e!ort to meet the prescribed NO  and particulate concentrations (see www.diesel- net.com). As admitted by automotive manufacturers, further improvements in combustion chamber and in fuel-injection design will not be su$cient to ful"l these emission standards, so that new after treatment appar- atus will be needed. An ambitious way to Diesel particulate removal is by using "lters carrying a suitable catalyst, which enables simultaneous soot "ltration and combustion. By these means, the #ue gas pressure drop across the "lter would never reach high values (resulting in a fuel penalty) and also "lter thermal stresses (occurring in non-catalytic traps as a consequence of sudden burn-o! of large amounts of trapped particulate) could be reduced to a minimum level. The "lter characteristics must ensure a good compromise between high "ltration e$ciency, low-pressure drop and good penetration/dispersion of particulate inside the trap matrix. This last is an impor- tant condition to allow the catalyst to get in contact with a signi"cant amount of "ltered soot particles. Among the various "lter types, ceramic foams seem to be the best, especially to meet these last requirements since they enable a deep-bed "ltration instead of a shallow-bed one (wall-#ow "lters). The present paper concerns some of the most recent experimental results obtained by our group in an indus- trial-type BRITE EURAM project (CATATRAP) fo- cused on diesel particulate removal through catalytic 0009-2509/01/$-see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S0009-2509(00)00389-4