The epitaxial growth of ZnO films on Cu(111) surface: Thickness dependence

Thang, Ho Viet; Tosoni, Sergio; Pacchioni, Gianfranco

doi:10.1016/j.apsusc.2019.03.240

Cited by 12 publications

(6 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…During DFT optimizations, bottom two layers were fixed while the rest were allowed to relax with adsorbates. The optimized structure of stoichiometric ZnO flat overlayer showed a nonpolar graphite-like structure instead of the polar wurtzite structure, which is in consistent with recent reports that ZnO graphitic structures were observed experimentally or calculated theoretically when only thin layers (≤ 4) of ZnO grown on metal supports. ,− …”

Section: Experimental and Computational Methodssupporting

confidence: 89%

Selective Methane Oxidation to Methanol on ZnO/Cu₂O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

et al. 2021

View full text Add to dashboard Cite

Because of the abundance of natural gas in our planet, a major goal is to achieve a direct methane-to-methanol conversion at medium to low temperatures using mixtures of methane and oxygen. Here, we report an efficient catalyst, ZnO/ Cu 2 O/Cu(111), for this process investigated using a combination of reactor testing, scanning tunneling microscopy, ambientpressure X-ray photoemission spectroscopy, density functional calculations, and kinetic Monte Carlo simulations. The catalyst is capable of methane activation at room temperature and transforms mixtures of methane and oxygen to methanol at 450 K with a selectivity of ∼30%. This performance is not seen for other heterogeneous catalysts which usually require the addition of water to enable a significant conversion of methane to methanol. The unique coarse structure of the ZnO islands supported on a Cu 2 O/ Cu(111) substrate provides a collection of multiple centers that display different catalytic activity during the reaction. ZnO−Cu 2 O step sites are active centers for methanol synthesis when exposed to CH 4 and O 2 due to an effective O−O bond dissociation, which enables a methane-to-methanol conversion with a reasonable selectivity. Upon addition of water, the defected O-rich ZnO sites, introduced by Zn vacancies, show superior behavior toward methane conversion and enhance the overall methanol selectivity to over 80%. Thus, in this case, the surface sites involved in a direct CH 4 → CH 3 OH conversion are different from those engaged in methanol formation without water. The identification of the site-dependent behavior of ZnO/Cu 2 O/Cu(111) opens a design strategy for guiding efficient methane reformation with high methanol selectivity.

show abstract

Section: Experimental and Computational Methodssupporting

confidence: 89%

Selective Methane Oxidation to Methanol on ZnO/Cu₂O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

et al. 2021

View full text Add to dashboard Cite

show abstract

“…This shows that the adsorption of CO on top of thicker ZnO islands can result in a sizable blue shift in the CO stretching mode without the need to assume that a transition to the wurtzite structure has occurred. This is consistent with a recent theoretical analysis [19] that showed that for free-standing ZnO films, a flat graphite-like morphology is preferred up to 10 layers, where a transition to wurtzite-like structures occurs. On Cu(111), a slightly corrugated graphitic structure is obtained for ZnO films up to 4 layers.…”

Section: Coadsorption Of D O and Co On Zno Bilayer-supported Zno Clussupporting

confidence: 93%

“…[9][10][11][12][13][14][15][16] Metal-supported ZnO thin films are known to feature tunable structural and chemical properties which differ substantially from those of the bulk wurtzite ZnO. [17][18][19][20][21][22][23][24][25][26][27][28] To date, experimental and theoretical works have focused predominantly on well-defined two-dimensional ZnO films, many of them of bilayer thickness, while much less information is available about small ZnO clusters (or islands) supported on such ZnO bilayers.…”

Section: Introductionmentioning

confidence: 99%

Chemical Reactivity of Supported ZnO Clusters: Undercoordinated Zinc and Oxygen Atoms as Active Sites

Roth

Wang

et al. 2020

ChemPhysChem

Self Cite

View full text Add to dashboard Cite

The growth of ZnO clusters supported by ZnO-bilayers on Ag(111) and the interaction of these oxide nanostructures with water have been studied by a multi-technique approach combining temperature-dependent infrared reflection absorption spectroscopy (IRRAS), grazing-emission X-ray photoelectron spectroscopy, and density functional theory calculations. Our results reveal that the ZnO bilayers exhibiting graphite-like structure are chemically inactive for water dissociation, whereas small ZnO clusters formed on top of these well-defined, yet chemically passive supports show extremely high reactivitywater is dissociated without an apparent activation barrier. Systematic isotopic substitution experiments using H 2 16 O/D 2 16 O/ D 2 18 O allow identification of various types of acidic hydroxyl groups. We demonstrate that a reliable characterization of these OH-species is possible via co-adsorption of CO, which leads to a red shift of the OD frequency due to the weak interaction via hydrogen bonding. The theoretical results provide atomic-level insight into the surface structure and chemical activity of the supported ZnO clusters and allow identification of the presence of under-coordinated Zn and O atoms at the edges and corners of the ZnO clusters as the active sites for H 2 O dissociation.

show abstract

“…However, compared to CuZn alloys, theoretical studies on the cationic Zn are still rather limited due to the lack of valid structure models. There were a few attempts to construct the likely structural models, including ZnO overlayer on Cu(111), − ZnO x cluster on Cu(111), , and Zn x O y H z clusters on Cu(111). , As a representative, Kattel et al proposed an interesting ZnOH model with a Zn 6 O 7 H 7 cluster on Cu(111) (Figure a) and obtained the TOF of 0.09 s –1 for methanol synthesis by DFT calculations and kMC simulation, which is close to the experimental TOF.…”

Section: Discussion On the Active Sitementioning

confidence: 58%

Methanol Synthesis from CO₂/CO Mixture on Cu–Zn Catalysts from Microkinetics-Guided Machine Learning Pathway Search

et al. 2022

View full text Add to dashboard Cite

Methanol synthesis on industrial Cu/ZnO/Al 2 O 3 catalysts via the hydrogenation of CO and CO 2 mixture, despite several decades of research, is still puzzling due to the nature of the active site and the role of CO 2 in the feed gas. Herein, with the large-scale machine learning atomic simulation, we develop a microkinetics-guided machine learning pathway search to explore thousands of reaction pathways for CO 2 and CO hydrogenations on thermodynamically favorable Cu−Zn surface structures, including Cu(111), Cu(211), and Zn-alloyed Cu(211) surfaces, from which the lowest energy pathways are identified. We find that Zn decorates at the step-edge at Cu(211) up to 0.22 ML under reaction conditions with the Zn−Zn dimeric sites being avoided. CO 2 and CO hydrogenations occur exclusively at the step-edge of the (211) surface with up to 0.11 ML Zn coverage, where the low coverage of Zn (0.11 ML) does not much affect the reaction kinetics, but the higher coverages of Zn (0.22 ML) poison the catalyst. It is CO 2 hydrogenation instead of CO hydrogenation that dominates methanol synthesis, agreeing with previous isotope experiments. While metallic steps are identified as the major active site, we show that the [−Zn−OH−Zn−] chains (cationic Zn) can grow on Cu(111) surfaces under reaction conditions, which suggests the critical role of CO in the mixed gas for reducing the cationic Zn and exposing metal sites for methanol synthesis. Our results provide a comprehensive picture on the dynamic coupling of the feed gas composition, the catalyst active site, and the reaction activity in this complex heterogeneous catalytic system.

show abstract

The epitaxial growth of ZnO films on Cu(111) surface: Thickness dependence

Cited by 12 publications

References 51 publications

Selective Methane Oxidation to Methanol on ZnO/Cu₂O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

Selective Methane Oxidation to Methanol on ZnO/Cu₂O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

Chemical Reactivity of Supported ZnO Clusters: Undercoordinated Zinc and Oxygen Atoms as Active Sites

Methanol Synthesis from CO₂/CO Mixture on Cu–Zn Catalysts from Microkinetics-Guided Machine Learning Pathway Search

Contact Info

Product

Resources

About

The epitaxial growth of ZnO films on Cu(111) surface: Thickness dependence

Cited by 12 publications

References 51 publications

Selective Methane Oxidation to Methanol on ZnO/Cu2O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

Selective Methane Oxidation to Methanol on ZnO/Cu2O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

Chemical Reactivity of Supported ZnO Clusters: Undercoordinated Zinc and Oxygen Atoms as Active Sites

Methanol Synthesis from CO2/CO Mixture on Cu–Zn Catalysts from Microkinetics-Guided Machine Learning Pathway Search

Contact Info

Product

Resources

About

Selective Methane Oxidation to Methanol on ZnO/Cu₂O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

Selective Methane Oxidation to Methanol on ZnO/Cu₂O/Cu(111) Catalysts: Multiple Site-Dependent Behaviors

Methanol Synthesis from CO₂/CO Mixture on Cu–Zn Catalysts from Microkinetics-Guided Machine Learning Pathway Search