Diesel Soot Combustion: Catalyst Formulation to Avoid Reaction Runaway

M.A. PERALTA, C.A. QUERINI

Houston, USA

Congreso; 20th North American Catalysis Society Meeting; 2007

ACS

One of the alternatives to avoid diesel soot particles being emitted to the environment, is employing a filter placed in the automovile exhaust pipe (1). The soot deposited on the filter must be continously burnt to avoid high pressure dropped, which would lead to the engine failure. The temperature needed to burn the soot, in a non-catalityc way, is too high (above 550ºC) to be reached in normal operations conditions. One of the alternatives to solve this problem is depositing a catalyst on the filter walls (2), so as the soot can be burnt continuously in the normal operations conditions. One of the problems found in these systems is an eventual reaction runaway, produced when accumulating large amounts of soot on the catalyst. In that situation, temperatures as high as 1500ºC could be reached, which would lead to the filter failure. The K/La2O3 catalyst was studied for soot combustion. This catalyst in contact with water and CO2 forms like-hydroxide and like-carbonate compounds (3). Some of these formed compounds, decompose in the same temperature range in which soot combustion occurs, absorbing part of the released heat during soot combustion. The simultaneity of both process (decomposition and combustion) would lead to a lower total heat releasing in the system soot-catalyst-filter, thus preserving the characteristics and increasing the life-time of the catalyst-filter system. This catalyst is compared with another, K/CeO2, which has similar soot combustion activity (4).