Abstract
This Perspective focuses on the characterization of supported metal catalysts by operando and CO infrared (IR) spectroscopy. CO IR spectroscopy is a powerful technique for probing catalyst surfaces and is used to identify single-atom catalysts, estimate metal surface availability to the gas phase, and measure catalyst Lewis acidity. However, the interpretation of CO IR spectra on metal surfaces is not trivial and is influenced by dipole-dipole interactions among CO molecules at medium to high coverage. Such a phenomenon results in spectral distortions, such as intensity transfer among IR bands, the appearance of spurious bands, and shifts in band position. Dipole-dipole interactions were widely investigated and understood from the 1950s to 1990s, but the implications for operando spectroscopy have been seemingly overlooked in the literature, with a few exceptions. Inspired by seminal studies in the field, I propose here the use of mixed isotopic streams, such as diluted 13CO in 12CO, to reduce dipole coupling effects and retrieve more information from operando IR spectra in reactions involving CO, such as CO oxidation or hydrogenation reactions. Similarly, mixed 13CO2/12CO2 streams may be applied in CO2 hydrogenation, where adsorbed CO is commonly observed. The proposed name of the technique is Mixed Isotope Operando IR Spectroscopy, MIOIRS. In this Perspective, I will first summarize the nature of dipole-dipole interactions in adsorbed CO layers and their effects on CO IR spectra. Then, I will briefly describe how diluted isotopic mixtures of CO can partially break the coupling among adsorbates and reduce spectral distortion. In both sections, I will give a few showcases of the implications of vibrational coupling in the characterization of heterogeneous catalysts. Finally, I will discuss the possible implications of MIOIRS for the detection and quantification of defect and surface sites on metal nanoparticles, the characterization of bimetallic nanoparticles surfaces, and the kinetics of CO intermediates adsorbed on different active sites. Notably, MIOIRS may be expanded to other reactions in which adsorbates have strong permanent dipoles, such as in self-catalytic reduction for NOx abatement.
Original language | English |
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Pages (from-to) | 1363-1386 |
Number of pages | 24 |
Journal | ACS Catalysis |
Volume | 15 |
Issue number | 2 |
Early online date | 8 Jan 2025 |
DOIs | |
Publication status | Published - 17 Jan 2025 |
Bibliographical note
Publisher Copyright:© 2025 The Author. Published by American Chemical Society.
Funding
The Advanced Research Center Chemical Building Blocks Consortium (ARC CBBC) is acknowledged for funding.
Funders | Funder number |
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Advanced Research Center Chemical Building Blocks Consortium (ARC CBBC) |
Keywords
- carbon monoxide
- catalyst characterization
- dipole−dipole interactions
- isotopic labeling
- operando infrared spectroscopy
- vibrational coupling