Equilibrium and kinetics of NO and CO chemisorptions an nonstoichiometric nickel-copper manganites

The equilibrium and kinetics of adsorption of NO and CO on nonstoichiometri c nickel-copper manganites have been investigated through volumetric measur ements. The adsorption isotherms were satisfactorily fitted to the Freundli ch equation. The equilibrium coverages at 298 K were found to depend closel y on the chemical composition of the oxide; thus, a decrease in the coverag e beyond a maximum copper extent was observed. The adsorption isotherms of NO at various temperatures in the range from 298 to 473 K showed that the e quilibrium coverage decreases with increasing temperature. This behavior en abled us to follow the logarithmic decrease of the heat of adsorption of NO on such surfaces. The adsorptions of NO and CO on surfaces preadsorbed wit h CO and NO, respectively, were also studied. These experiments showed the ability of NO to displace CO preadsorbed molecules whereas the contrary did not hold, suggesting the existence of common adsorption sites as well as s ome specific CO adsorption sites. Finally, some kinetic data are reported s howing that the experimental adsorption results fit the Elovich equation (w ith t(0) approximate to 0), although two distinct rate processes could be i dentified. (C) 2000 Academic Press.