NO reduction by CH4 in the presence of excess O2 over Pd/sulfated zirconia catalysts

The selective catalytic reduction (SCR) of NO by methane in the presence of excess oxygen has been studied on a series of Pd catalysts supported on sulfated zirconia (SZ). This support is not as sensitive to structural damage by steaming as the acidic zeolites, such as H-ZSM-5 and H-Mor. In previous studies, it was shown that this type of acidic zeolites are able to stabilize Pd²⁺ ions and promote high SCR activity and selectivity, which are typically not seen in Pd catalysts. In this contribution, it has been demonstrated that SZ is able to promote the NO reduction activity in a similar way to the acidic zeolites, by stabilizing Pd²⁺ ions that is selective for NO reduction. As in the case of acidic zeolites, the stabilization of Pd²⁺ ions can occur through a transfer of Pd species from particle to particle. One of the attractive features of Pd/SZ catalysts is that they are less sensitive to water and SO₂ poisoning than Pd/H-ZSM-5 catalyst and exhibit higher reversibility after removal of water or SO₂.