(674d) CO and C3H6 oxidation on Pd-Based Three-Way Catalysts: Effects of Loading and Aging Protocols on Particle Size Calculation

In stoichiometric gasoline engines, three-way catalysts (TWCs) are used to curb tailpipe emissions of unburned hydrocarbons, CO, NOx and other pollutants. Due to the high price and low abundance of precious metals used in TWC formulations, there has been significant research exploring improving precious metal utilization through new formulations and enhanced synthesis methods. Kinetic studies can then be performed to assess the CO and C₃H₆ oxidation activity of these newly synthesized TWCs, and a combination of chemisorption and spectroscopic techniques would normally be used to determine the number of exposed metal sites and, therefore, reaction rates.

Newly synthesized TWCs may contain various promoters that could potentially interfere with the particle size calculation (i.e., carbonate formation on the catalyst surface during CO adsorption, O spillover from the support to the metal site), chemisorption protocols must be modified to alleviate these issues. Literature results have shown that by pre-exposing the catalyst surface with CO₂, the overestimation of particle size calculation during CO adsorption on CeO₂-containing catalysts was corrected, and a more accurate particle size was obtained [1]. Inspired by these results, we adapted a CO chemisorption protocol to include a CO₂ pre-adsorption phase before CO adsorption. The lack of carbonate formation on the supports after CO chemisorption was verified using DRIFTS. This technique was applied to a series of Pd-based catalysts with different loading, aged at different temperatures and on different supports. CO oxidation kinetics were also performed to confirm that the particle sizes measured coincide with the structure insensitivity of CO oxidation.

References

[1] Takeguchi, T., Manabe, S., Kikuchi, R., Eguchi, K., Kanazawa, T., Matsumoto, S., & Ueda, W. (2005). Determination of dispersion of precious metals on CeO2- containing supports. Applied Catalysis A: General, 293(1–2), 91–96. https://doi.org/10.1016/j.apcata.2005.07.013