New Direct Evaluation of Oxygen Storage/Release Capacity on Millisecond Time Scale

The amount of oxygen storage and release from catalysts on a millisecond scale (MS-OSC) is believed to play an essential role in automotive three-way catalysts. We have developed a new method to evaluate the MS-OSC based on the rapid detection of reaction products on catalyst surfaces immediately after CO and O2 injections using pulsed valves by time-of-flight mass spectrometry. CO and O2 were passed over the surface of a slurry-coated catalyst on a planar cordierite substrate initially under high vacuum (10Pa). This allowed the MS-OSC to be directly evaluated as the amount of CO2 without gas diffusion effects. We applied this MS-OSC measurement technique to the following three catalysts: Pt/CeO2-ZrO2 (CeO2:ZrO2 = 1:1); Pt/CeO2-ZrO2 (CeO2:ZrO2 = 5:1); and Pt/CeO2ZrO2-Y2O3 (CeO2:ZrO2:Y2O3 = 46.5:46.5:7.0). Pt/CeO2-ZrO2-Y2O3 was reported to improve the transient catalytic activity on a millisecond scale, which could not be explained by conventional thermo-gravimetric OSC measurements on the scale of seconds. Among these three catalysts, Pt/CeO2-ZrO2-Y2O3 was found to have the highest MS-OSC. This is supported by a previously reported set of engine test results.