Effect of NOx and C3H6 partial pressures on the activity of Pt-beta-coated cordierite monoliths for deNOx C3H6-SCR

The influence of NOx and C3H6 partial pressures (from 500 to 2000 ppm) in NOx reduction under O-2-rich conditions, catalyzed by a Pt-beta-coated monolith, has been studied. Reactivity measurements in the temperature range from 170 to 240 degrees C were carried out in a horizontal reactor at 5600 h(-1). NOx reduction is not affected by C3H6 and NOx concentration from 170 to 190 degrees C, only depending on temperature. Above 190 degrees C, NOx reduction increases as the NOx/C3H6 ratio decreases. The temperatures for the maximum NOx reduction and total C3H6 conversion are not coupled for all gas compositions. At temperatures lower than 200 degrees C, C3H6 NOx reaction is predominant, and above a certain temperature that depends on the gas composition, the C3H6-O-2 reaction is the main C3H6-conversion pathway. This behaviour is consistent with NOx reduction and C3H6 conversion activation energies (72 +/- 11 and 133 +/- 18 kJ/mol, respectively). At temperature higher than 200 degrees C, the mass transfer of reactants affects the overall reaction rate. For practical application, the temperature window of the process is between 190 and 220 degrees C, but the actual temperature must be selected depending on the gas composition. (c) 2006 Elsevier B.V. All rights reserved.