Transient TPSR, DRIFTS-MS and TGA studies of a Pd/ceria-zirconia catalyst in CH 4 and NO 2 atmospheres

Abstract

In this study, the parameters governing the activity of Pd/ceria-zirconia catalysts in the selective catalytic reduction (SCR) of NO x assisted by methane are investigated using a combination of temperature-programmed spectroscopic and thermogravimetric techniques and transient SCR conditions. By DRIFTS of adsorbed CO, it is established that Pd species on Ce 0.2Zr 0.8O 2 are mainly present in cationic form but exhibit high reducibility. As found by temperature-programmed surface reaction (TPSR) in CH 4 + NO 2 atmosphere, the CH 4-SCR reaction is initiated at 280 °C on Pd/Ce 0.2Zr 0.8O 2 and yields almost 100% N 2 above 500 °C. DRIFTS-MS and TGA experiments performed under transient SCR conditions show that DeNO x activity is due to a surface reaction between some methane oxidation products on reduced Pd sites with ad-N x O y species presumably located on the support. The detrimental effect of O 2 on DeNO x is explained by the promotion of the total combustion of methane assisted by the ceria-zirconia component at the expense of the SCR reaction above 320 °C.