Dynamic carbon monoxide oxidation over platinum/alumina

Dynamic studies of CO oxidation have shown complex behavior such as rate enhancement and CO{dollar}sb2{dollar} peak formation during forced periodic operation. In this work, two Pt/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} catalysts with similar Pt dispersions, one prepared from a chloride-containing precursor and one prepared from a chloride-free precursor, were examined in terms of their steady-state reaction behavior and dynamic responses to periodic changes of CO pressure in O{dollar}sb2.{dollar} Numerical simulations of both steady-state and time-resolved dynamic reaction measurements are also performed. This is the first work to present direct comparisons of steady-state and rapid dynamic measurements to an elementary step model which accounts for the effects of internal diffusion and site heterogeneity in supported porous metal catalysts.; The results of the steady-state and dynamic experiments correlated with each other and with adsorption calorimetry and temperature programmed desorption (TPD) results, and indicated that the chloride-free sample had stronger CO-Pt interactions than the chloride-containing sample. Addition of HCl to the chloride-free catalyst did not have a significant effect on CO TPD, indicating that differences in surface structure distribution rather than residual chloride may have caused the differences in CO-Pt interactions. The results indicate that measurement of metal dispersion is not sufficient to characterize a supported metal catalyst for CO oxidation.; Comparisons indicate that classic single-adsorption-site Langmuir-Hinshelwood kinetics fail to predict the observed rates of reaction during dynamic operation. For CO cycling in O{dollar}sb2,{dollar} diffusion resistance inside the porous catalyst suppresses the CO{dollar}sb2{dollar} response during CO-on half-periods, in cases where CO cycling periods are similar to diffusion-limited adsorption times. Complex island and surface reconstruction models developed to predict dynamic behavior for CO oxidation cannot explain the observed steady-state and dynamic responses. The steady-state and time-resolved dynamic reaction measurements for both catalysts can be accurately predicted by a relatively simple elementary step model that specifies two distinct types of adsorption sites which differ only in rate constant for CO desorption and rate of surface reaction between adsorbed CO and O.