The selective catalytic reduction (SCR) of NO x by dodecane in excess oxygen-containing gas mixtures was studied on Ce and/or Pd-loaded HMOR. Under dry conditions the best fresh bimetallic catalyst, 6.2wt.%Ce–0.08wt.%Pd-HMOR, displayed a maximum of about 70% NO x conversion to N 2 at 350°C and GHSV=30,000h −1 , while either Ce-HMOR or Pd-HMOR exhibited low activity for the SCR reaction. The presence of both Ce and Pd in the zeolite was crucial for high deNO x activity. The dodecane concentration is very important for the reaction. The catalyst is not active in the absence of the reducing agent and inhibition of NO x reduction is observed at dodecane concentrations higher than 440–500ppm. The presence of 40ppm SO 2 in the gas feed suppresses the reaction. However, the coexistence of 15% H 2 O and 40ppm SO 2 has no appreciable effect on the catalyst activity. Enhanced activity and a broader temperature window was observed in the NO 2 +dodecane+O 2 reaction in the presence of 15% H 2 O and 100ppm SO 2 . In this reaction mixture, the catalyst was capable of retaining a stable NO 2 conversion to N 2 for a period of ten days. Characterization by XPS and UV–VIS–diffuse reflectance spectra (UV–VIS–DRS) of selected fresh and aged catalyst samples indicates that Pd exists mainly as Pd 2+ cations in Ce–Pd-HMOR. Cerium is mostly present as CeO 2 on the surface of the zeolite particles. However, part of the cerium in 6Ce–Pd-HMOR, exists as stable Ce 3+ species.