Activity Function for Describing Alteration of Three-Way Catalyst Performance over Palladium-Only Three-Way Catalysts by Catalyst Mileage

Abstract

A simple three-way catalyst (TWC) activity function based upon the alteration of the Pd metallic surface area (MSA) of Pd-only commercial monolith TWCs has been developed to describe the change of the catalytic performance with respect to the Pd metal loading varying from 5 to 10 g/L and the field-aged catalyst mileage from 4K (stabilized) to 98K miles. Particularly, the change of the Pd MSA of TWC with respect to the catalyst mileage has been well-correlated by the second-order sintering kinetics, regardless of the Pd content of the TWC. The TWC activity function was incorporated into the primary reaction kinetics developed for the stabilized 4K Pd-only TWCs to predict the deactivation of the Pd-only TWC performance with respect to the field-aged mileage. The overall reaction kinetic model with the TWC activity function developed in the present study is capable of describing the alteration of TWC performance with respect to the catalyst mileage, regardless of the catalyst metal content. ' INTRODUCTIONThe development of the catalyst activity function is useful for predicting the life of the catalyst for designing a commercial catalytic reactor, since more than 90% of the heterogeneous catalytic process experiences a decay of the reaction rate with respect to the reactor on-stream time. 1 The activity function can be obtained by correlating the rates at any time to time zero, although it requires exhaustive time and effort including the collection and test of the deactivated catalyst samples under practical operating conditions with respect to the duration of their uses. Another approach may be the independent development of an activity function based upon the alteration of the physicochemical properties of the catalyst including the content of the deactivation precursors, such as coke, sulfur, and contaminants, the metal dispersion, and the catalyst surface area. 2À4 The deactivation of the activity and durability of three-way catalyst (TWC) installed into gasoline driven cars is apparent as the catalyst mileage increases. 5 Furthermore, the technical and market demands for developing the deactivation model to predict the life of TWC becomes inevitable for the design of the TWC catalytic converter to meet the ever-tightening emission regulations throughout the world and the mileage guarantee by automakers. 6 However, a TWC activity function directly describing the alteration of TWC performance has been rarely reported, mainly due to the difficulty in collecting of the catalyst samples with respect to the catalyst mileage and the complexity of the deactivation of commercial TWC under the real driving condition.Ekstr€ om et al. predicted the decline of the catalytic activity of TWC aged under accelerated engine bench condition by the simple adjustment of the frequency factor of the rate constant included in the primary kinetics. 7 Baba et al. developed a TWC deactivation kinetics based upon the change of the frequency factor attributed to both sintering of Pt metal and phosphorus poisoning under accelerated engin...

In operando Detection of Three-Way Catalyst Aging by a Microwave-Based Method: Initial Studies

“…Since the aging degree of a TWC is correlated with its light-off temperature [22], and since the resonance frequency depends on catalyst temperature [6], the first series of experiments investigated the temperature dependence of the samples at different aging states in light-off experiments. At each aging state of the catalyst sample, three light-off experiments were conducted.…”

Modeling of the Interactions Between Catalytic Surfaces and Gas-Phase

“…The ratio F cat=geo ¼ A cat A geo is also used to describe the dependence of the overall reaction rate on catalyst loading and effects of hydro-thermal aging for structure-insensitive catalysts [61]. Practically, it was recently applied to model the performance of on-road aged three-way catalysts [62].…”

Kinetic model for modern double-layered Pd/Rh TWC as a function of metal loadings and mileage

“…(5) was combined with the detailed reaction kinetics developed for the 4 k Rh15 reference catalyst to predict the TWC performance as a function of the Rh loading and the catalyst mileage as follows [3,5,9]:…”

“…The overall reaction kinetics (R i ) for the double-layered Pd/Rh monolith catalyst in terms of the Pd and Rh loadings and the catalyst mileage was developed by combining both activity functions (a Pd and a Rh ) with their corresponding reference reaction kinetics [3,8,9,11]: where R i. is the intrinsic reaction kinetics of the double-layered Pd/ Rh monolith TWC at a specific catalyst mileage (M) and PGM loadings including both Pd (L Pd ) and Rh (L Rh ), a Pd and a Rh are the activity function for the Pd-based TWCs, Eq. (S1) [8] and that for the Rhbased TWCs, Eq.…”

“…To quantify the effect of the PGM loading and catalyst mileage on the performance variation of automotive catalytic systems, the concept of activity function has been introduced on the basis of the variation of the active metal surface area (MSA) of the Pdbased TWC [3,8,9]. A similar approach has been applied to the Pt-based diesel oxidation catalyst (DOC) through the use of a scaling factor to adjust the frequency factor of the reaction rate constant [5,10].…”