| 1. |
|
|
| 2. |
- Besharat, Zahra, et al.
(författare)
-
Dehydrogenation of methanol on Cu2O(100) and (111)
- 2017
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 146:24
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption and desorption of methanol on the (111) and (100) surfaces of Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120-620 K, in combination with density functional theory calculations and sum frequency generation spectroscopy. The bare (100) surface exhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (root 3 x root 3)R30 degrees-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surface oxygen.
|
|
| 3. |
- Marks, Kess, 1987-, et al.
(författare)
-
Adsorption and decoposition of ethanol on Cu2O(111) and (100)
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:33, s. 20384-20392
-
Tidskriftsartikel (refereegranskat)abstract
- Ethanol dehydrogenation on metal oxides such as Cu2O is an important reaction for the production of renewable energy by fuel cells both via the production of H2 fuel and applied in direct alcohol fuel cells. To better understand this reaction we studied the adsorption, dissociation and desorption of ethanol on Cu2O(111) and (100) surfaces using high-resolution photoelectron spectroscopy (PES), vibrational sum frequency generation spectroscopy (SFG), and temperature programmed desorption (TPD) accompanied by density functional theory (DFT) calculations. On Cu2O(100) the first layer consists primarily of dissociatively adsorbed ethoxy. Second and third layers of ethanol physisorb at low temperature and desorb below 200 K. On the Cu2O(111) surface, adsorption is mixed as ethoxy, ethanol and the products following C-C cleavage, CHx and OCHx, are found in the first layer. Upon heating, products following both C-C and C-O bond breaking are observed on both surfaces and continued heating accentuates the molecular cracking. C-O cleavage occurs more on the (100) surface, whereas on the Cu2O(111) C-C cleavage dominates and occurs at lower temperatures than on the (100) surface. The increased ability of Cu2O(111) to crack ethanol is explained by the varied surface structure including both surface oxygen, electron rich O-vacancies and Cu.
|
|
| 4. |
- Soldemo, Markus, et al.
(författare)
-
Cuprous oxide surfaces exposed to sulfur dioxide and near-ambient pressures of water
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The interaction of sulfur dioxide with Cu2O(100) and Cu2O(111) at ultra-high vac-uum is studied. It is found that on both surfaces, the sulfur dioxide moleculesbind as SO3-species. Dosing water in UHV does not impact the SO3-species at thedoses used. When dosing water at near-ambient pressure conditions, however, itis observed that the sulfur in the SO3-species shifts to Cu2S when monitoring thePES S 2p-region.
|
|
| 5. |
- Soldemo, Markus, et al.
(författare)
-
Interaction of sulfur dioxide and near-ambient pressures of water vapor with cuprous oxide surfaces
- 2017
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:43, s. 24011-24024
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of water vapor and sulfur dioxide (SO2) with single crystal cuprous oxide (Cu2O) surfaces of (100) and (111) termination was studied by photoelectron spectroscopy (PES) and density functional theory (DFT). Exposure to near-ambient pressures of water vapor, at 5 × 10-3 %RH and 293 K, hydroxylates both Cu2O surfaces with OH coverage up to 0.38 copper monolayers (ML) for (100) and 0.25 ML for (111). O 1s surface core level shifts indicate that the hydroxylation lifts the (3,0;1,1) reconstruction of the clean (100) surface. On both clean Cu2O terminations, SO2 adsorbs to unsaturated surface oxygen atoms to form SO3 species with coverage, after a saturating SO2 dose, corresponding to 0.20 ML on the Cu2O(100) surface and 0.09 ML for the Cu2O(111) surface. Our combined DFT and PES results suggest that the SO2 to SO3 transformation is largely facilitated by unsaturated copper atoms at the Cu2O(111) surface. SO3-terminated surfaces exposed to low doses of water vapor (=100 langmuirs) in ultrahigh vacuum show no adsorption or reaction. However, during exposure to near-ambient pressures of water vapor, the SO3 species dissociate, and sulfur replaces a Cu2O lattice oxygen in a reaction that forms Cu2S. The hydroxylation of the Cu2O surfaces is believed to play a central role in the reaction.
|
|
| 6. |
- Soldemo, Markus, et al.
(författare)
-
The Surface Structure of Cu2O(100)
- 2016
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:8, s. 4373-4381
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu2O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu2O(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 x 2), and (1 x 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 x 1) surface structure. The most common termination of Cu2O(100) has previously been described by a (3 root 2 x root 2)R45 degrees unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results.
|
|
