Nitric oxide reduction with methane over Pd/TiO2 catalysts .1. Effect of oxygen concentration

Steady-state reaction studies were performed over a Pd/titania catalyst for NO reduction using CH4 as a reducing agent. The catalyst was prepared 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 electron microscopy (SEM), and thermal analysis techniques. A fixed-bed, flow reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were done on-line using gas chromatography-mass spectrometry, chemiluminescence, and wet chemistry techniques. Temperature-programmed reduction studies indicated that the catalyst was reducible by H-2 even at sub-ambient temperatures. The catalyst was seen to reduce NO with conversions above 95% in the oxygen concentration range from 0 to 1.3%. Oscillatory behavior was exhibited by the catalyst under certain reaction conditions. The results obtained from the reaction experiments, together with the findings from the characterization studies, are used to explain the mechanistic aspects of this reaction. (C) 1997 Academic Press.