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Title: Coupling of Acetaldehyde to Crotonaldehyde on CeO 2–x (111): Bifunctional Mechanism and Role of Oxygen Vacancies

Abstract

Selective C–C coupling of oxygenates is pertinent to the manufacture of fuel and chemical products from biomass and from derivatives of C 1 compounds (i.e., oxygenates produced from methane and CO 2). Here we report a combined experimental and theoretical study on the temperature-programmed reaction (TPR) of acetaldehyde (AcH) on a partially reduced CeO 2–x(111) thin film surface. The experiments have been carried out under ultra-high-vacuum conditions without continuous gas exposure, allowing better isolation of active sites and reactive intermediates than in flow reaction conditions. AcH does not undergo aldol condensation in a typical TPR procedure, even though the enolate form of AcH (CH 2CHO) is readily produced on CeO 2–x(111) with oxygen vacancies. We find however that a tailored “double-ramp” TPR procedure is able to successfully produce an aldol adduct, crotonaldehyde (CrA). Using density functional theory calculations and microkinetic modeling we explore several possible C–C coupling pathways. We conclude that the double-ramp procedure allows surface oxygen vacancy dimers, stabilized by adsorbate occupation, to form dynamically during the TPR. The vacancy dimers in turn enable C–C coupling to occur between an enolate and an adjacent AcH molecule via a bifunctional enolate–keto mechanism that is distinct from conventional acid- or base-catalyzedmore » aldol condensation reactions. Here, the proposed mechanism indicates that CrA desorption is rate-limiting while C–C coupling is facile.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [3];  [4]; ORCiD logo [3]; ORCiD logo [1]
  1. Louisiana State Univ., Baton Rouge, LA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Princeton Univ., Princeton, NJ (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) CONICET—UNL, Santa Fe (Argentina)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS) (SC-27)
OSTI Identifier:
1506811
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 123; Journal Issue: 13; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Zhao, Chuanlin, Watt, Charles L., Kent, Paul R., Overbury, Steven H., Mullins, David R., Calaza, Florencia C., Savara, Aditya, and Xu, Ye. Coupling of Acetaldehyde to Crotonaldehyde on CeO 2–x (111): Bifunctional Mechanism and Role of Oxygen Vacancies. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.8b08535.
Zhao, Chuanlin, Watt, Charles L., Kent, Paul R., Overbury, Steven H., Mullins, David R., Calaza, Florencia C., Savara, Aditya, & Xu, Ye. Coupling of Acetaldehyde to Crotonaldehyde on CeO 2–x (111): Bifunctional Mechanism and Role of Oxygen Vacancies. United States. doi:10.1021/acs.jpcc.8b08535.
Zhao, Chuanlin, Watt, Charles L., Kent, Paul R., Overbury, Steven H., Mullins, David R., Calaza, Florencia C., Savara, Aditya, and Xu, Ye. Wed . "Coupling of Acetaldehyde to Crotonaldehyde on CeO 2–x (111): Bifunctional Mechanism and Role of Oxygen Vacancies". United States. doi:10.1021/acs.jpcc.8b08535. https://www.osti.gov/servlets/purl/1506811.
@article{osti_1506811,
title = {Coupling of Acetaldehyde to Crotonaldehyde on CeO 2–x (111): Bifunctional Mechanism and Role of Oxygen Vacancies},
author = {Zhao, Chuanlin and Watt, Charles L. and Kent, Paul R. and Overbury, Steven H. and Mullins, David R. and Calaza, Florencia C. and Savara, Aditya and Xu, Ye},
abstractNote = {Selective C–C coupling of oxygenates is pertinent to the manufacture of fuel and chemical products from biomass and from derivatives of C1 compounds (i.e., oxygenates produced from methane and CO2). Here we report a combined experimental and theoretical study on the temperature-programmed reaction (TPR) of acetaldehyde (AcH) on a partially reduced CeO2–x(111) thin film surface. The experiments have been carried out under ultra-high-vacuum conditions without continuous gas exposure, allowing better isolation of active sites and reactive intermediates than in flow reaction conditions. AcH does not undergo aldol condensation in a typical TPR procedure, even though the enolate form of AcH (CH2CHO) is readily produced on CeO2–x(111) with oxygen vacancies. We find however that a tailored “double-ramp” TPR procedure is able to successfully produce an aldol adduct, crotonaldehyde (CrA). Using density functional theory calculations and microkinetic modeling we explore several possible C–C coupling pathways. We conclude that the double-ramp procedure allows surface oxygen vacancy dimers, stabilized by adsorbate occupation, to form dynamically during the TPR. The vacancy dimers in turn enable C–C coupling to occur between an enolate and an adjacent AcH molecule via a bifunctional enolate–keto mechanism that is distinct from conventional acid- or base-catalyzed aldol condensation reactions. Here, the proposed mechanism indicates that CrA desorption is rate-limiting while C–C coupling is facile.},
doi = {10.1021/acs.jpcc.8b08535},
journal = {Journal of Physical Chemistry. C},
number = 13,
volume = 123,
place = {United States},
year = {2018},
month = {10}
}

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