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

Journal Article · · Topics in Catalysis
 [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)
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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.

Research Organization:
National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)
Sponsoring Organization:
USDOE Office of Fossil Energy (FE)
Grant/Contract Number:
FE0004000
OSTI ID:
1478389
Journal Information:
Topics in Catalysis, Journal Name: Topics in Catalysis Journal Issue: 5-6 Vol. 61; ISSN 1022-5528
Publisher:
SpringerCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (1)

Synergic and Antifouling Effect of ZnO on Ethanol Oxidation by Silver-Palladium Bimetallic Electrocatalyst journal January 2019

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Density functional theory
Formaldehyde
Methanol oxidation
Minimum energy pathway
Temperature programmed reaction spectroscopy
Ultrathin ZnO