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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 H-2 fuel and via application 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, vibrational sum-frequency generation spectroscopy, and temperature-programmed desorption accompanied by density functional theory calculations. On Cu-2(100), the first layer consists primarily of dissociatively adsorbed ethoxy. Second and third layers of ethanol physisorb at low temperatures 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 molecular cracking. C-O cleavage occurs more on the (100) surface, whereas on the Cu2O(111) surface, C-C cleavage dominates and occurs at lower temperatures than those for the (100) surface. The increased ability of Cu2O(111) to crack ethanol is explained by the varied surface structure including surface oxygen, electron-rich O vacancies, and Cu., QC 20190923

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 theorycalculations and sum frequency generation spectroscopy. The bare (100) surfaceexhibits 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 (√3 × √3)R30°-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 surfaceoxygen., QC 20170816

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., QC 20171116

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., QC 20160406

High-resolution photoemission spectroscopy and scanning tunneling microscopy (STM) have been used to investigate defects on Cu2O(111) and their interaction with water and sulfur dioxide (SO2). Two types of point defects, i.e., oxygen and copper vacancies, are identified. Copper vacancies are believed to be the most important defects in both water and SO2 surface chemistry. Multiply coordinatively unsaturated oxygen anions (OMCUS) such as oxygen anions adjacent to copper vacancies are believed to be adsorption sites for both water and SO2 reaction products. Water adsorption at 150 K results in both molecular and dissociated water. Molecular water leaves the surface at 180 K. At 300 K and even more at 150 K, SO2 interacts with oxygen sites at the surface forming SO 3 species. However, thermal treatment up to 280 K of Cu 2O(111)/SO2 prepared at 150 K renders only SO4 on the surface., QC 20140224

Photoelectron spectroscopy has been used to study room temperature adsorption of sulfur dioxide on clean and water exposed (0001) surfaces of zinc and zinc oxide. Water has no significant effect either on clean or on SO2 exposed Zn(0001) at the low water pressures used (p < 10(-7) mbar). In the Case of the zinc-terminated ZnO(0001) surface, however, water adsorbs dissociatively and OH groups are shown to have a considerable effect on SO2 surface reactions. A strong oxidation reaction occurs between Zn(0001) and SO2 giving various sulfur containing species. On ZnO(0001), SO2 interacts mainly with oxygen sites giving SO3 or SO4 species. It is shown that the ZnO(0001) sample preparation procedure can have large effects on surface chemical and physical properties. Samples cleaned by four different preparation procedures are investigated, namely sputtering only and sputtering followed by annealing at 450 degrees C, 530 degrees C and 600-650 degrees C. Annealing at 600 degrees C leads to a transition from a partly OH-terminated surface to a triangularly structured surface free from OH groups. Adsorption of SO2 on the latter surface leads to a decreased surface conductivity, which hampers photoemission measurements. Water is shown to block SO2 adsorption sites on both 450 degrees C and 530 degrees C annealed samples. On the latter sample. SO2 reduction has been observed to a small extent on the clean surface and to a larger extent when the surface is prehydroxylated. Here, we speculate that water, similar to hydrogen, generates surface zinc clusters on ZnO(0001). Zinc clusters could enable charge transfer to the antibonding LUMO of the SO2 molecule and subsequent dissociation., QC 20130125

We present room temperature scanning tunneling microscopy and photoemission spectroscopy studies of water adsorption on the Zn-terminated ZnO(0001) surface. Data indicates that the initial adsorption is dissociative leaving hydroxyl groups on the surface. At low water coverage, the adsorption occurs next to the oxygen-terminated step edges, where water is believed to bind to zinc cations leaving off hydrogen atoms to under-coordinated oxygen anions. When increasing the water dose, triangular terraces grow in size and pits diminish until the surface is covered with wide irregular terraces and a large number of small pits. Higher water exposure (20 Langmuir) results in a much more irregular surface. Hydrogen, which is produced in the dissociation reaction is believed to have an important role in the changed surface structure at high exposures. The fact that adsorbed water completely changes the structure of ZnO(0001) is an important finding toward the understanding of this surface at atmospheric conditions., QC 20101216

Thin films of titanyl phthalocyanine (TiOPc) have been adsorbed on InSb(1 1 1) (3 x 3) and InSb(1 0 0) c(8 x 2) surfaces and studied with respect to their electronic structure using photoemission (PES), density functional theory (DFT) and scanning tunneling microscopy (STM). The interface chemical interaction is weak in both cases; no adsorbate induced surface band bending is observed and the energy level alignment across the interface is determined by the original position of the substrate Fermi level and the charge neutrality level of the molecule. Room temperature adsorption results in disordered films on both surfaces. The behaviors after annealing are different; on InSb(1 0 0) well-ordered molecular chains form along and on top of the In-rows, whereas on (1 1 1) no long range order is observed. The disorder leads to intermolecular interactions between the titanyl group and neighboring benzene rings leading to a split of TiOPc HOMO (highest occupied molecular orbital) by as much as 0.8 eV., QC 20100525

We present angle-resolved photoelectron spectroscopy data probing the electronic structure of the Nd-substituted high-T-c cuprate La1.48Nd0.4Sr0.12CuO4. Data have been acquired at low and high photon energies, h nu=55 and 500 eV, respectively. The two extracted Fermi surfaces show significant differences. The differences can be attributed to either the change in probing depth suggesting dissimilarity of the intrinsic electronic structure between surface and bulk regions, or a considerable c-axis dispersion signaling a strong interlayer coupling. At both photon energies, considerable spectral weight is observed at all points along the Fermi surface and the intensity distribution as well as Fermi-surface shape observed at low as well as high photon energy is markedly different from what has been previously reported for La1.28Nd0.6Sr0.12CuO4 by Zhou [Science 286, 268 (1999)]. Document Type: Article, QC 20100702

Low-energy electron diffraction and scanning tunneling microscopy have been used to probe the surface atomic structure Of Cu2O(111) after various sample preparations. Annealing in oxygen gives a stoichiometric (1 x 1) oxygen terminated surface and further annealing in ultra-high vacuum results in a clear (root 3 x root 3)R30 degrees reconstruction and surface faceting. Tunneling from filled states in the reconstructed surface reveals a hexagonal pattern of large protrusions, which show an internal structure. The reconstruction is believed to be due to one-third of a monolayer of ordered oxygen vacancies. At areas on the surface where the large features are missing, another smaller type of protrusions is visible, which is associated with the ideal (1 x 1) surface. The relative position of the two types of features gives two possible models of the (111) surface. In the first model, the (1 x 1) surface is the ideal bulk terminated surface and coordinatively unsaturated oxygen ions are missing in the reconstructed surface. The second model agrees with the first model with the exception that coordinatively unsaturated copper ions in the outmost copper layer are missing in both the (1 x 1) and the reconstructed surface. The latter model is supported by previous surface free energy calculations. Since the undercoordinated copper ions have been suggested to be the catalytic active sites Of Cu2O(111), the presence or absence of these cations could be of great importance for the fundamental understanding of the surface reactivity Of Cu2O and of copper-based catalysts., QC 20100525

We present scanning tunneling microscopy of an octahedral (B) plane terminated (root 2 x root 2)R45 degrees-reconstructed surface of a natural magnetite (10 0) crystal. Implementing a W-tip we achieve the same resolution on Fe rows as was reported in the past either with the use of antiferromagnetic tips or on magnetite (Fe3O4) films. We show images of Fe or O sublattices of Fe3O4 with atomic resolution., QC 20100525

We present angle-resolved photoemission data along the M-Gamma-M direction from a Cu2O(111) single crystal, collected at high photon energies (h nu=619 and 891 eV) and T=100 K. Because of the high photon energies and effective background subtraction, our data give a clear picture of the bulk band structure. The results confirm the existence of a hybridized Cu 3d-Cu 4s state located between the two main Cu 3d and O 2p band regions. Several theoretical studies have predicted the existence of this band, but until now it has not been detected in any photoemission measurements. The experimentally derived band structure is compared to local density approximation calculations with and without the Hubbard potential U. The clear band dispersion in our experimental data has enabled us to extract a refined Hubbard U value, which makes it possible to achieve a better agreement between theoretically calculated bands and experimental data., QC 20100702

We have investigated the initial stages of titanyl phthalocyanine (TiOPc) growth on single crystalline ZnO(0 0 0 1). This organic-semiconductor interface is self-organizing as a 2 x 1 pattern appears in a low energy electron diffraction upon deposition of the molecules. To achieve this pattern, the TiOPc is suggested to adsorb standing with the edge of the molecule along the substrate atomic rows. Photoelectron spectroscopy is used to further analyze the interface; a relatively large upwards band bending amounting to 0.5 eV is found and a splitting of the molecules highest occupied molecular orbital occurs after thermal treatment, indicating that the molecules are lying down., QC 20100812

The authors present a high-resolution core-level photoemission study of a Fe3O4(100) surface exposed to 50 L (1 L=10(-6) mbar s) of H2O and 50 L of SO2. S 2p core-level spectra reveal the presence of SO3 and SO4 species. An additional peak in the Fe 3p core-level spectrum shows that they bond with iron from the substrate. Complementary scanning tunneling microscopy of the same surface demonstrates formation of a long-range ordered sulfate locked in the (root 2x root 2)R45 degrees-surface potential., QC 20100525

QS 2011

QS 2011

QC 20161107, methanol, metal oxides and catalysis, Cu2O

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., QC 20161114