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

The influence of NOx and C3H6 partial pressures (from 500 to 2000 ppm) in NOx reduction under O2-rich conditions, catalyzed by a Pt-beta-coated monolith, has been studied. Reactivity measurements in the temperature range from 170 to 240 °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 °C, only depending on temperature. Above 190 °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 °C, C3H6–NOx reaction is predominant, and above a certain temperature that depends on the gas composition, the C3H6–O2 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 °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 °C, but the actual temperature must be selected depending on the gas composition.