Behavior of Non-Promoted and Ceria-Promoted Pt/Rh and Pd/Rh Three-Way Catalysts under Steady State and Dynamic Operation of Hybrid Vehicles

Abstract

The suitability of newly developed non-promoted and ceria-promoted palladium−rhodium automotive catalysts for the exhaust gas control of a hybrid drive system has been tested by light-off experiments with steady and cycling feed stoichiometry, and pulsed-flow operation. The dynamic behavior of the honeycomb-type catalysts has been compared to the performance of standard honeycomb platinum−rhodium catalysts. Light-off tests carried out in the range 150−500 °C indicated significant differences in the conversion of NO x , CO, and hydrocarbons during warm-up, depending on the catalyst composition and whether λ-cycling was applied or not. Appropriate λ-cycling substantially improved the behavior of all catalysts in the lower light-off region. At higher temperatures cycling afforded lower conversions of all target components. Under pulsed-flow operation with an air pulse preceding the exhaust pulse (filling of the cylinder with air), asymmetric λ-cycling with longer rich half-cycles resulted in CO and HC conversions as well as N2 yields similar to or higher than those without an air pulse for the ceria-promoted catalysts. The catalytic tests suggest that ceria-promoted palladium is competitive to Pt−Rh−Ce in a hybrid vehicle application.

Modeling of an Automotive Exhaust Gas Converter at Low Temperatures Aiming at Control Application

“…External heating has not been considered in this study, while secondary air injection will be discussed later. Many researchers have reported a conversion improvement due to oscillatory feed to the converter, which is the result of the control loop [8,10]. These reports have usually been based on experimental work.…”

“…The adsorption rate of component i (i=CO, O 2 , NO, C 2 H 2 and C 2 H 4 ) on the noble metal site is given by: (6) while the adsorption rate coefficients are obtained from the kinetic gas theory: 7The desorption rate of adsorbed species j (j=CO*, NO*, C 2 H 4 ** and C 2 H 2 ****) is proportional to the surface coverage of that species and is given by: (8) Oxygen desorption can be neglected at the temperatures considered. The rates of surface reactions are proportional to the product of surface coverages of involved species (x,y): (9) Both desorption and surface reaction rate coefficients are of the Arrhenius type: (10) Basically the same rate equations, as described above, are applied for the adsorption of oxygen on the ceria surface and the reaction between oxygen and CO adsorbed on the noble metal surface. The only difference is that the oxygen storage capacity, L OSC , is used instead of the noble metal capacity, L NM .…”

“…The catalytic converter behavior under different operating conditions can be investigated experimentally [8,9,10], and by means of modeling. The computer models are very beneficial for the converter optimization.…”

Coreduction methodology for immiscible alloys of CuRu solid-solution nanoparticles with high thermal stability and versatile exhaust purification ability

“…Even Rh, the most famous exhaust puri-cation catalyst, cannot simultaneously purify CO, NO x and hydrocarbon species up to 100%, it also requires Pt and Pd as co-catalysts for complete CO conversion. 34 Notably, under the conditions of the similar loading amount and the same alumina support, the CuRu solid solution catalyst exhibited close conversion with Pd/Rh and Pt/Rh catalysts in NO reduction and hydrocarbon oxidation, but did not match with Pd/Rh and Pt/ Rh catalysts in CO conversion; 35 this may be due to a relatively large mean diameter for CuRu NPs (Fig. S37, S38 †).…”

Unsteady-state operation of supported platinum catalysts for high conversion of methane

“…For example it has been shown that by use of periodic operation of the gas composition, the light-o↵ temperature for conversion of hydrocarbons can be lowered by 50-75 C over a TWC [6,7]. In this case the benefit with periodic operation is mainly due to a lowering of the CO self-poisoning, which has previously been studied in detail [8,9,10,11].…”