CO Oxidation over Oxide Supported Platinum Catalysts
Abstract: Catalytic oxidation of carbon monoxide (CO) is one of the most studied reactions that still needs to be improved because of its practical use in the chemical industry including feedstock purification and applications such as emission control, in-door air cleaning, improvement of fuel cell efficiency, etc. Concerning CO emissions, the transportation sector is a large contributor. The development of modern powertrains and driving patterns lead to cold exhausts. Thus, catalysts must be active for CO oxidation at low temperatures, which is a challenge. Further, CO oxidation is influenced by other compounds in the exhausts that may either promote or inhibit essential catalytic functions. For combustion exhausts, water is definitely inevitable and nitrogen oxides are common components. This work scrutinizes the kinetics of CO oxidation over Pt/alumina and Pt/ceria catalysts through analysis of reaction orders obtained experimentally from flow-reactor measurements and theoretically by kinetic Monte Carlo simulations and connects this to kinetic model formulation. Further, the catalytic structure-function relationship is explored by operando infrared and X-ray absorption spectroscopy. The influence of water and nitrogen oxide on the CO oxidation kinetics is investigated with in situ infrared spectroscopy. Finally, iron oxide is explored as an active support for platinum with a focus on the structural dynamics of Pt/FeOx under reaction conditions. The results show that reaction orders depend on reaction conditions and operating mechanism, and the adsorbate-adsorbate interactions play a crucial role. Pt/ceria is active at lower temperatures than Pt/alumina thanks to lattice oxygen in the ceria support that participates according to a Mars-van Krevelen mechanism. This mechanism is promoted by water but inhibited by nitrogen oxide through nitrate formation. On Pt/alumina, the reaction proceeds via the Langmuir-Hinshelwod mechanism, which is also promoted by water and inhibited by nitrates. Finally, using iron oxide as support for Pt opens for a catalyst design with a support even more interacting with Pt than ceria in terms of redox properties at low temperatures.
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