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Because the exhaust composition in closed-loop emission control systems fluctuates about the stoichiometric set point, there is considerable interest in understanding and improving catalyst behavior in this oscillating environment. We have measured adsorption capacities, responses to step changes in feedstream composition, and performance in cycled laboratory feedstreams in order to clarify features of the transient response of three-way catalysts. Our laboratory results are best explained on the basis of a temporary increase in water-gas shift activity rather than the more common oxygen storage explanation. The phenomenon is associated with the presence of rhodium in the catalyst and Is enhanced when cerium is also present. Sulfur dioxide in the feedstream was highly detrimental to the water-gas shift reaction; so the applicability of these results to the exhaust environment remains an open question.

Williamson, W. B.; Gandhi. H. S. SA€ 1980, 800843. Tittareili, P.; Iannibeiio, A.; Villa, P. L. J. SolM State Chem. 1981, 3 7 , 95.The oxidations of ethanol and acetaldehyde were studied in a laboratory flow reactor over alumina-supported catalysts containing 4 wt % Cu-2 wt % Cr, 0.1 wt % Pt, and 4 wt % Mn, respectively. Most experiments were carried out in feedstreams consisting of 0.1 vol % ethanol or 0.025 vol % acetaldehyde and 1 % O2 in nitrogen at a space velocity of 52 000 (volume feedHvolume catalyst)-' h-' (STP). All three catalysts were found to produce acetaldehyde, carbon monoxide, and carbon dioxide as the major carbon-contalnlng products of ethanol oxidation. CO, was the principal carbon-containing product in the oxidation of acetaldehyde. The steady-state yield of acetaldehyde obtained in the oxidation of ethanol was found to go through a maximum as the temperature was raised over each catalyst. The data suggest that some of the ethanol is oxidized consecutively to acetaldehyde and then to COP over these catalysts. In addition, over Pt, there is also evidence for the direct oxidation of ethanol to co,.The kinetics of the copper-catalyzed amination of long-chain aliphatic alcohols (octanol and decanol) by monomethylamine and dimethylamine have been investigated in both the gas and liquid phases at temperatures between 440 and 540 K. The Individual reactions leadlng to the production of stable intermediates and products are identified. The rate of dehydrogenation of the alcohol determines the overall rate of alcohol conversion to all products. The rate i s first order in alcohol in both the gas and liquid phases and inhibited by alcohol, water, and the reactant amine in the gas phase only. The selectivity is determined primarily by the rate of hydrogenation of an adsorbed intermediate and the rate of disproportionation of reactant and product amines. The selectivity of the amination reaction to the desired tertlary amine increases with increasing hydrogen pressure, and first increases and then decreases with increasing conversion of alcohol.

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The exhaust composition in closed-loop emission control systems typically oscillates about the stoichiometric set point. We describe herein the laboratory system we developed to investigate catalyst behavior in such an environment. The design is such that the frequency, amplitude, and average composition of the oscillations can be varied independently of one another. In laboratory testing of a platinum-rhodium catalyst it was demonstrated that the "window" for three-way conversion could be Improved via oscillations of low frequency or large amplitude, but peak conversion efficiencies were sacrificed in the process. On samples aged in engine exhaust or at high temperature, cycling effects were most evident under near-stoichiometric conditions.