IR Studies of Ethoxy Groups on CeO2.
Jerzy Podobiński1, Małgorzata Zimowska1, Michał Śliwa1
1Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow, Poland.
Molecules (Basel, Switzerland)
|February 11, 2023
Summary
The reaction of ethanol on cerium dioxide (CeO2) surfaces forms ethoxy groups and water, with species type varying by surface reduction or oxidation. Monodentate ethoxyls are most reactive during oxidation.
Area of Science:
- Surface Chemistry
- Catalysis
- Materials Science
Background:
- Cerium dioxide (CeO2) is a key material in catalysis due to its redox properties.
- Understanding surface reactions is crucial for optimizing catalytic processes.
- Ethanol oxidation is relevant to fuel conversion and chemical synthesis.
Purpose of the Study:
- To investigate the reaction mechanism of ethanol on CeO2 surfaces.
- To characterize different ethoxy species formed on CeO2.
- To determine the influence of CeO2 surface pre-treatment (reduction/oxidation) on ethanol adsorption and reaction.
Main Methods:
- Infrared (IR) spectroscopy was employed to study ethanol adsorption and reaction.
- CeO2 surfaces were subjected to various pre-treatments: vacuum heating, hydrogen reduction, and oxygen oxidation.
- Reactions were studied at different ethanol coverages and temperatures.
Main Results:
- Ethanol adsorption forms ethoxy groups and surface hydroxyl (OH) groups.
- Water formation occurs at higher ethanol coverages, consuming surface Ce-OH.
- Three types of ethoxyls (monodentate, bidentate, tridentate) were identified based on IR spectral features.
- CeO2 reduction favored tridentate ethoxyls, while oxidation favored monodentate ethoxyls.
- At elevated temperatures, ethoxy groups oxidized to acetate ions, regenerating surface OH groups.
- Monodentate ethoxyls showed higher reactivity towards oxidation compared to tridentate ethoxyls.
- Oxidized CeO2 surfaces yielded the highest amounts of acetate species.
Conclusions:
- The surface state of CeO2 significantly influences the adsorption and reaction pathways of ethanol.
- The type of ethoxy species formed dictates their reactivity and subsequent oxidation products.
- Surface reduction and oxidation treatments offer pathways to tune the catalytic behavior of CeO2 for ethanol conversion.
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