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.
Zhao, Chuanlin, et al. "Coupling of Acetaldehyde to Crotonaldehyde on CeO <sub>2–<i>x</i></sub> (111): Bifunctional Mechanism and Role of Oxygen Vacancies." Journal of Physical Chemistry. C, vol. 123, no. 13, Oct. 2018. https://doi.org/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 (2018). Coupling of Acetaldehyde to Crotonaldehyde on CeO <sub>2–<i>x</i></sub> (111): Bifunctional Mechanism and Role of Oxygen Vacancies. Journal of Physical Chemistry. C, 123(13). https://doi.org/10.1021/acs.jpcc.8b08535
Zhao, Chuanlin, Watt, Charles L., Kent, Paul R., et al., "Coupling of Acetaldehyde to Crotonaldehyde on CeO <sub>2–<i>x</i></sub> (111): Bifunctional Mechanism and Role of Oxygen Vacancies," Journal of Physical Chemistry. C 123, no. 13 (2018), https://doi.org/10.1021/acs.jpcc.8b08535
@article{osti_1506811,
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},
title = {Coupling of Acetaldehyde to Crotonaldehyde on CeO <sub>2–<i>x</i></sub> (111): Bifunctional Mechanism and Role of Oxygen Vacancies},
annote = {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},
url = {https://www.osti.gov/biblio/1506811},
journal = {Journal of Physical Chemistry. C},
issn = {ISSN 1932-7447},
number = {13},
volume = {123},
place = {United States},
publisher = {American Chemical Society},
year = {2018},
month = {10}}
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS) (SC-27)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1506811
Journal Information:
Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 13 Vol. 123; ISSN 1932-7447
