Abstract
Platinum and palladium are frequently used as catalytic materials, for example for the oxidation of CO. This is one of the most widely studied reactions in the field of surface science. Although seemingly uncomplicated, it remains an active and interesting topic, which is partially explained by the push to conduct experiments on model systems under relevant reaction conditions. Recent developments in the surface-science methodology have allowed obtaining chemical and structural information on the active phase of model catalysts. Tools of the trade include near-ambient-pressure X-ray photoelectron spectroscopy, high-pressure scanning tunneling microscopy, high-pressure surface X-ray diffraction, and high-pressure vibrational spectroscopy. Interpretation is often aided by density functional theory in combination with thermodynamic and kinetic modeling. In this review, results for the catalytic oxidation of CO obtained by these techniques are compared. On several of the Pt and Pd surfaces, new structures develop in excess O2. For Pt, this requires a much larger excess of O2 than for Pd. Most of these structures also develop in pure O2 and are identified as (surface) oxides. A large body of evidence supports the conjecture that these oxides are more reactive than the corresponding O-covered metallic surfaces under similar conditions, although still debated in the literature. An outlook on this developing field, including directions that move away from CO oxidation towards more complex chemistry, concludes this review.
Highlights
IntroductionAware that this review is not the first (see for example ref. 1–5) and certainly not the last to focus on CO oxidation over Pt and Pd, we will shortly motivate the need for ‘‘yet another
Aware that this review is not the first and certainly not the last to focus on CO oxidation over Pt and Pd, we will shortly motivate the need for ‘‘yet anotherMatthijs A. van Spronsen received his PhD degree in physics under the directorship of Prof
As similar structures can be prepared by cooling the sample and exposing it to low pressures of CO under UHV, a pressure gap is not present
Summary
Aware that this review is not the first (see for example ref. 1–5) and certainly not the last to focus on CO oxidation over Pt and Pd, we will shortly motivate the need for ‘‘yet another. His research interests include behavior of model catalysts under realistic reaction conditions and the development of instruments to probe surfaces in these environments. Joost Frenken is the Director of the Advanced Research Center for Nanolithography (ARCNL) in Amsterdam and a professor of Physics at both universities in Amsterdam (UvA and VU) and at Leiden University His scientific expertise is in the structure, diffusion, chemical reactions, phase transitions and friction phenomena at surfaces and interfaces, investigated using advanced. These papers originated from two separate scientific fields; from heterogeneous catalysis and from surface science The former traditionally focuses on how to synthesize and characterize the most active catalysts, while trying to extract details regarding the reaction mechanism, structure of the active sites, etc. The conditions under which this occurs are strongly dependent on the sample and reactor geometry
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