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Title: Methanol Oxidation to Formaldehyde Promoted at the Step Sites of Ultrathin ZnO

Adsorption and oxidation of methanol on ultrathin ZnO layers supported on Au(111) have been investigated using temperature programmed reaction spectroscopy (TPRS) and density functional theory (DFT) calculations. In the TPRS experiments, following adsorption of methanol- 18O at T = 100 K, only molecular methanol- 18O desorbed from the planar ZnO bilayer surface at T = 220 and 260 K, whereas a partial oxidation product, formaldehyde- 18O (~95% selectivity), and a small amount of carbon dioxide (C 16O 18O) were produced at T = 580 K at the bilayer–trilayer step sites. The DFT calculations were used to identify the adsorption configurations of methanol on the planar ZnO surface and at the step sites, as well as the reaction pathways to gaseous formaldehyde. The most stable adsorption configuration corresponds to methanol molecule adsorbed at the bilayer–trilayer step sites with its C–O axis parallel to the upper terrace edge, forming a bond between its O atom and a Zn site on the lower terrace, and also a hydrogen bond between its H atom in the OH group and a lattice O anion at the upper terrace edge. Starting from the most stable adsorption configuration at the step sites, formation of gaseous formaldehyde wasmore » found to take place preferentially via a methoxy (CH 3O(ad)) intermediate. This process follows the pathways CH 3OH(ad) → CH 3O(ad) + H(ad) → CH 2O(g) + 2H(ad) and has an overall barrier of 19.0 kcal/mol. The reaction pathway to produce a lattice O-bonded formaldehyde (H 2COOlattice(ad)), the proposed precursor leading to CO 2, was found to be energetically less favorable with a barrier of ~38 kcal/mol. As a result, the preference to produce gaseous formaldehyde from the DFT calculations agrees well with the high selectivity toward formaldehyde observed in the TPRS experiments.« less
Authors:
 [1] ;  [2] ;  [1]
  1. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); AECOM, South Park, PA (United States)
  2. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)
Publication Date:
Grant/Contract Number:
FE0004000
Type:
Accepted Manuscript
Journal Name:
Topics in Catalysis
Additional Journal Information:
Journal Volume: 61; Journal Issue: 5-6; Journal ID: ISSN 1022-5528
Publisher:
Springer
Research Org:
National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)
Sponsoring Org:
USDOE Office of Fossil Energy (FE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Methanol oxidation; Formaldehyde; Ultrathin ZnO; Temperature programmed reaction spectroscopy; Density functional theory; Minimum energy pathway
OSTI Identifier:
1478389

Deng, Xingyi, Sorescu, Dan C., and Lee, Junseok. Methanol Oxidation to Formaldehyde Promoted at the Step Sites of Ultrathin ZnO. United States: N. p., Web. doi:10.1007/s11244-017-0867-0.
Deng, Xingyi, Sorescu, Dan C., & Lee, Junseok. Methanol Oxidation to Formaldehyde Promoted at the Step Sites of Ultrathin ZnO. United States. doi:10.1007/s11244-017-0867-0.
Deng, Xingyi, Sorescu, Dan C., and Lee, Junseok. 2018. "Methanol Oxidation to Formaldehyde Promoted at the Step Sites of Ultrathin ZnO". United States. doi:10.1007/s11244-017-0867-0.
@article{osti_1478389,
title = {Methanol Oxidation to Formaldehyde Promoted at the Step Sites of Ultrathin ZnO},
author = {Deng, Xingyi and Sorescu, Dan C. and Lee, Junseok},
abstractNote = {Adsorption and oxidation of methanol on ultrathin ZnO layers supported on Au(111) have been investigated using temperature programmed reaction spectroscopy (TPRS) and density functional theory (DFT) calculations. In the TPRS experiments, following adsorption of methanol-18O at T = 100 K, only molecular methanol-18O desorbed from the planar ZnO bilayer surface at T = 220 and 260 K, whereas a partial oxidation product, formaldehyde-18O (~95% selectivity), and a small amount of carbon dioxide (C16O18O) were produced at T = 580 K at the bilayer–trilayer step sites. The DFT calculations were used to identify the adsorption configurations of methanol on the planar ZnO surface and at the step sites, as well as the reaction pathways to gaseous formaldehyde. The most stable adsorption configuration corresponds to methanol molecule adsorbed at the bilayer–trilayer step sites with its C–O axis parallel to the upper terrace edge, forming a bond between its O atom and a Zn site on the lower terrace, and also a hydrogen bond between its H atom in the OH group and a lattice O anion at the upper terrace edge. Starting from the most stable adsorption configuration at the step sites, formation of gaseous formaldehyde was found to take place preferentially via a methoxy (CH3O(ad)) intermediate. This process follows the pathways CH3OH(ad) → CH3O(ad) + H(ad) → CH2O(g) + 2H(ad) and has an overall barrier of 19.0 kcal/mol. The reaction pathway to produce a lattice O-bonded formaldehyde (H2COOlattice(ad)), the proposed precursor leading to CO2, was found to be energetically less favorable with a barrier of ~38 kcal/mol. As a result, the preference to produce gaseous formaldehyde from the DFT calculations agrees well with the high selectivity toward formaldehyde observed in the TPRS experiments.},
doi = {10.1007/s11244-017-0867-0},
journal = {Topics in Catalysis},
number = 5-6,
volume = 61,
place = {United States},
year = {2018},
month = {3}
}

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