Influence of composition of reaction mixture NO + CO + O/sub 2/ on catalytic properties and state of surface of supported noble metals. II. Pd/. gamma. -Al/sub 2/O/sub 3/

IR spectroscopy has been used in determining the sources of the deactivating effect of CO and O/sub 2/ in the reaction of NO reduction by carbon monoxide in the presence of oxygen on Pd/..gamma..-Al/sub 2/O/sub 3/. IR spectra were taken with separate and joint chemisorption of NO and CO, and also directly under the conditions of the reaction, with a ratio m = ((NO) + 2(O/sub 2/))/(CO) from 0.69 to 1.62. The observed nitrosyl and carbonyl complexes are stabilized on Pd in different degrees of oxidation. The lower NO conversions in mixtures with excess CO are explained by competitive adsorption of NO and CO. With increasing concentration of O/sub 2/ up to 0.3% by volume (m = 1.15), the degree of oxidation of the Pd increases. Along with this, there is a decrease in the bond strength in Pd-CO complexes, and favorable conditions are created for chemisorption and activation of NO molecules. The lower NO conversions when m > 1.15 are due to further oxidation of the palladium, on which, apparently, dissociative chemisorption of NO is suppressed. Formation conditions and properties are examined for -NCO surface isocyanate complexes localized on the support and -NCO and -CN complexes that are presumablymore » bound to the active components.« less