Cyclic operation of platinum/alumina catalysts for carbon monoxide oxidation

Abstract

An experimental investigation of CO oxidation over well-characterized Pt/Al203 catalysts in an integral reactor under the conditions of forced feed composition cycling is presented, and various ways for possible improvements in the cyclic performance of automotive catalysts are considered. The effects of time-average feed composition, as well as of catalyst impregnation depth, on the cyclic performance are also examined. The results indicate that the most effective operating strategy for CO oxidation over Pt/Al203 catalysts is a hybrid scheme: cyclic operation during the warm-up period up to 300 °C and steady operation for temperatures above 300 °C. In the hightemperature range above 350 °C, the reaction yield for the stoichiometric cyclic operation may be improved by increasing the partial pressure of reactants. The chromatographic and antlchromatographic effects on the catalyst activity during cyclic operation are discussed.

Modeling dynamic phenomena in 3-way catalytic converters

“…The frequency and the width of the oscillation are determined by the response characteristics of the fuel management control loop. Several and often contradicting views have been expressed in the past, regarding the e!ect of the oscillation on catalyst e$ciency (Cho, 1988;Muraki et al, 1985;Shinjoh et al, 1989;Cho and West, 1986). In the interesting review of Silveston (1996) it is concluded that the periodic oscillations are bene"cial during the cold start phase, when the catalyst operates at low temperatures, but they can be unfavorable at high-temperature operation.…”

Dynamic behavior issues in three‐way catalyst modeling

“…Several often contradicting views regarding the effect of the oscillation on catalyst efficiency were Ž expressed in the past Cho, 1988;Muraki et al, 1985;Shinjoh . et al, 1989;Cho and West, 1986 . In the interesting review of Ž . Silveston 1996 it is concluded that the periodic oscillations are beneficial during the cold-start phase, when the catalyst operates at low temperatures, but they can be unfavorable at high-temperature operation.…”

Effect of engine exhaust gas modulation on the cold start emissions

“…The effects of variations in exhaust gas air-fuel ratio and composition have been shown to alter the catalyst pollutant conversion performance (Silveston, 1996;Shamim and Medisetty, 2003;Shamim, 2005). Particularly, at temperatures below light-off values, the exhaust gas composition modulation has been found to result in a significant rate enhancement for CO oxidation over catalyst (Cutlip, 1979;AbdulKareem et al, 1980;Schlatter and Mitchell, 1980;Taylor and Sinkevitch, 1983;Cho and West, 1986;Zhou et al, 1986). Cho (1988) found higher conversions for all three pollutants by feed composition modulation around a timeaverage stoichiometric point below the reaction light-off temperature.…”