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This study used in situ modulation excitation spectroscopy (MES) with varying frequencies in a single experiment to identify surface species during ethanol oxidation on Au/SiO2, Au/TiO2, Au/ZnO, and Au/SrTiO3. Fixed-bed reactor (FBR) tests (1 kPa ethanol, 1.5 kPa O2, 513 K) showed that Au/SiO2 and Au/SrTiO3 had higher ethanol conversions. Au/SiO2 favored acetaldehyde, while Au/SrTiO3 yielded more acetates (acetic acid and ethyl acetate). Operando modulation excitation (ME)–phase sensitive detection (PSD)–DRIFTS, with ethanol and oxygen modulation, identified surface ethanol, acetaldehyde, acetates, ethoxy, and hydroxyl species. Oxygen modulation showed charge transfer to supports in Au/TiO2 and Au/ZnO. At the fundamental frequency (f0 = 1/90 Hz), ME–PSD–DRIFTS showed minimal adsorbed ethanol on Au/SiO2, indicating high ethanol conversion. Au/SrTiO3 had higher acetaldehyde consumption, correlating with increased acetates, consistent with FBR results. ME–PSD–DRIFTS at lower frequencies (0.07f0, 0.5 f0) and higher harmonics (2f0, 3f0) showed rapid ethoxy formation/decomposition, and slower acetaldehyde reactions, confirming acetaldehyde as a primary product and acetates as secondary products. Oxygen modulation revealed rapid hydrogen spillover and hydroxyl changes. Overall, operando spectroscopy via mass spectrometry confirmed the FBR findings.
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Flow Electrolyzer Mass Spectrometry with a Gas‐Diffusion Electrode Design
Abstract Operando mass spectrometry is a powerful technique to probe reaction intermediates near the surface of catalyst in electrochemical systems. For electrochemical reactions involving gas reactants, conventional operando mass spectrometry struggles in detecting reaction intermediates because the batch‐type electrochemical reactor can only handle a very limited current density due to the low solubility of gas reactant(s). Herein, we developed a new technique, namely flow electrolyzer mass spectrometry (FEMS), by incorporating a gas‐diffusion electrode design, which enables the detection of reactive volatile or gaseous species at high operating current densities (>100 mA cm−2). We investigated the electrochemical carbon monoxide reduction reaction (eCORR) on polycrystalline copper and elucidated the oxygen incorporation mechanism in the acetaldehyde formation. Combining FEMS and isotopic labelling, we showed that the oxygen in the as‐formed acetaldehyde intermediate originates from the reactant CO, while ethanol and n‐propanol contained mainly solvent oxygen. The observation provides direct experimental evidence of an isotopic scrambling mechanism.
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- Award ID(s):
- 1904966
- PAR ID:
- 10492709
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 6
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- 3277 to 3282
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/anie.202013713
