Ce effect on the selective catalytic reduction of NO with CH4 on Pd-mordenite in the presence of O2 and H2O

The activity, selectivity and stability of Pd/H-MOR and Ce–Pd/H-MOR catalysts for the selective catalytic reduction of NO with CH4 (SCR-CH4) were studied in O2 excess (4.1%) in the absence and presence of H2O (5%). The reaction was carried out in a 300–650 °C temperature range with a S.V. of ≅33,000 h−1. The characterization of fresh and used catalysts by FTIR spectroscopy of adsorbed CO and NO showed that the loss of NO conversion in H2O presence was due to a decreasing concentration of Pd2+ sites and to the parallel formation of PdO particles that enhanced CH4 combustion under dry conditions. This behavior was modified by Ce addition. Under wet conditions the Ce–Pd/H-MOR catalyst was very active (XNO = 76% at 550 °C), selective (100% of N2) and stable. The FTIR spectrum of CO adsorbed on used samples demonstrated that Ce inhibited the transformation of active Pd2+ into PdO particles. However, Ce presence also enhanced CH4 combustion under wet conditions. At low temperatures (<500 °C) H2O presence inhibited N2O formation and 90% selectivity to N2, which improved with Ce addition, was obtained.