Experimental and numerical analysis of the effects of thermal degradation on carbon monoxide oxidation characteristics of a three-way catalyst

Abstract

This work investigates oxygen-storage capacity (OSC) changes during thermal degradation in modern three-way catalysts. Two experiments are performed using catalysts with different degradation degrees to evaluate OSC and reaction rates. The CO₂ production test, where CO and O₂ are supplied at a constant temperature, shows decreased CO₂ production with more degraded catalysts and reduced purification. The CO₂ production test is conducted using transient temperature increases, showing that the maximum CO₂ production temperature increases with catalyst degradation. The results reveal an increase in activation energy in the oxygen desorption reaction caused by thermal degradation progresses and a decrease in OSC, resulting in temperature increases in the oxygen storage reaction. In the surface reaction and mass transport model considering the 30 elementary reactions, the predicted results are well-validated for CO₂ production, enabling good oxygen storage predictions based on actual data. These results can be used to predict OSC by formulating the changes in active site density and activation energy due to degradation.

Keywords: Catalyst aging; Emissions control; Gasoline engines; Modeling and simulation; Thermal degradation; Three-way catalyst.

Fig. 1

Schematic diagram of TWC on one of the precious metals supported.

Fig. 2

Comparative images of PGM and TPB sites with particle size changes due to degradation.

Fig. 3

Imaged figure of catalyst degradation.

Fig. 4

Separation of CO and O₂ in the CO₂ production test reaction.

Fig. 5

Example of an Ozawa plot applied to the CO-TPR test results conducted in this study.

Fig. 6

Schematic of the experimental setup used in the reactor test.

Fig. 7

Experimental method of CO-TPR test (time history of introduction timing and temperature for each gas type).

Fig. 8

Experimental method of CO₂ production test (time history of introduction timing and temperature for each gas type).

Fig. 9

Results of CO-TPR test at 20 deg.C/min.

Fig. 10

Results of CO-TPR test for Mild catalyst under various temperature increase rates.

Fig. 11

Experimental results of CO₂ production test at 300 deg.C.

Fig. 12

Experimental results of CO₂ production test at 400 deg.C.

Fig. 13

Results of moving average processing for CO-TPR test results at 20 deg.C/min (Dot line: second peak temperature for each catalysts).

Fig. 14

Results of moving average processing of CO-TPR test results for the Mild catalyst(Dot line: second peak temperature for each conditions of raising temperature).

Fig. 15

Results of CO₂ concentration history of CO-TPR test at Severe catalyst and 10 deg.C/min.

Fig. 16

Results of CO₂ concentration history of CO-TPR test at Fresh Al₂O₃ catalyst at each condition.

Fig. 17

Results of analysis using an Ozawa plot for each catalyst (Fresh CZ, Mild, and Severe).

Fig. 18

Boundaries at each active site in CO₂ production test for Fresh catalyst.

Fig. 19

Experimental results of CO₂ production test for Fresh Al₂O₃ catalyst at 300 deg.C.

Fig. 20

Experimental results of CO₂ production test for Fresh Al₂O₃ and Fresh CZ catalysts at 300 deg.C.

Fig. 21

Verification of CO₂ concentration and the residual CO concentration in the CO₂ production test (symbol: Experimental value, Line: Calculated value).

Fig. 22

Verification of Storage fraction in CO₂ production test.

Fig. 23

Verification of CO₂ concentration in CO₂ production test under different SV conditions at Fresh CZ catalyst.

Fig. 24

Verification of CO₂ concentration in CO₂ production test under different temperature conditions at Fresh CZ catalyst.