NITRIC-OXIDE REDUCTION WITH METHANE OVER PD TIO2 CATALYSTS .1. EFFECTOF OXYGEN CONCENTRATION/

Steady-state reaction studies were performed over a Pd/titania catalys t for NO reduction using CH4 as a reducing agent. The catalyst was pre pared using a wet impregnation technique and Pd-acetate as a precursor for palladium. Characterization of the catalyst samples was performed using the BET surface area technique, X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning e lectron microscopy (SEM), and thermal analysis techniques. A fixed-bed , flow reactor system was used for activity and selectivity measuremen ts. Identification and quantification of reaction effluents were done on-line using gas chromatography-mass spectrometry, chemiluminescence, and wet chemistry techniques. Temperature-programmed reduction studie s indicated that the catalyst was reducible by H-2 even at sub-ambient temperatures. The catalyst was seen to reduce NO with conversions abo ve 95% in the oxygen concentration range from 0 to 1.3%. Oscillatory b ehavior was exhibited by the catalyst under certain reaction condition s. The results obtained from the reaction experiments, together with t he findings from the characterization studies, are used to explain the mechanistic aspects of this reaction. (C) 1997 Academic Press.