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Stable isothermal multiplicities were observed during carbon monoxide oxidation in an integral reactor, filled with alumina supported platinum catalysts. The multiplicities were investigated in the conversion-temperature, conversion-inlet carbon monoxide concentration and conversion-mass flow rate domains.The region of multiplicities was found to widen significantly upon catalyst aging which enhanced the pellets' diffusive resistances.Several intermediate stable steady states were found between the highest and lowest steady states, both experimentally and theoretically.All the above phenomena could be well interpreted by the interactions of the kinetics of carbon monoxide oxidation with intrapellet diffusion resistances.f Computed from the random pore model ot Wakao and Smith (Smith, 1970). and given here at I a& and 838'K. D increases with the 1.40'h power of T.

The cross-flow monolith is a novel solid-state electrocatalytic reactor configuration. The solid-state reactor, in principle, can be used to generate electricity, co-generate electricity and useful chemicals, enhance the rate of certain catalytic reactions, or to electrolyze 0-containing compounds. The distinguishing feature of the cross-flow geometry is its inherently high 02-transfer area per unit volume, which gives rise to higher calculated power densities than conventional designs. A twodimensional mixing cell model was constructed to stimulate the distribution of species, temperature, and current density. Results are reported for the species conversion, temperature distribution, thermodynamic energy conversion efficiency, and volumetric power density of a model reaction (CO oxidation over Pt in an yttriadoped zirconia structure).

A detailed mathematical model of a single catalyst pellet has been developed to describe its behavior under transient conditions encountered during the warmup period of automobile exhaust catalytic converters. In contrast to the converter models previously reported in the literature, this model is capable of describing the time-dependent behavior of a composite catalyst pellet, and thus provides a convenient means of examining the effects of poison penetration and various noble metal impregnation strategies in the activity-time (rather than activitytemperature) domain.Extensive calculations were carried out to investigate the effects of various catalyst design parameters and converter operating conditions on the lightoff behavior of a spherical, platinum-alumina catalyst pellet. Due to the complex kinetics of the CO and hydrocarbon oxidation reactions, catalyst lightoff was found to exhibit interesting behavior with respect to variations of the system's design parameters and operating conditions. Graphs are presented to illustrate the parametric sensitivity of these effects. It has been widely recognized that a substantial fraction of the carbon monoxide and hydrocarbon emissions occurs during the first few minutes (i.e., warmup period) of the Federal Test Procedure (FTP) driving cycle. Therefore, it is crucial to improve converter warmup performance in order to meet automotive emission standards which mandate more stringent emission control. Since converter performance is a complex function of operating conditions, converter geometries, and catalyst properties, an empirical approach to the problem can be very costly and time-consuming; thus, mathematical modeling promises to be helpful in the development of catalytic converters with improved warmup performance.There are some important design parameters associated with catalyst pellets used in automobile catalytic converters. For example, the relative locations of noble metals Hegedus, 1978, Hegedus et al., 1979) and their impregnation depths (Hegedus and Summers, 1977) have been shown to have a strong influence on the performance and durability characteristics of automotive catalysts. Converter models previously developed (e.g., Kuo et al., 1971;Ferguson and Finlayson, 1974), however, were not designed to study the effects of the parameters associated with the design of the catalyst pellet.Recently, Becker and Wei (1976, 1977a) investigated the effects of the location of the active layer on the catalyst's activity for negative-order reaction systems, such as the oxidation of carbon monoxide over platinum. They used the isothermal effectiveness factor vs. Thiele modulus plot to compare the lightoff characteristics of catalysts with various impregnation patterns. Although this approach is useful in gaining insight into the change in catalysts' activity as temperature varies, it does not provide information about the time scale of catalyst lightoff. Such information is necessary for estimating time-integrated emissions. For this reason, we decided to explore the...