Methanol Adsorption and Oxidation on Reduced and Oxidized TbO<sub><i>x</i></sub>(111) Surfaces

Schaëfer, Andreas; Cartas, William; Rai, Raul; Shipilin, Mikhail; Merte, Lindsay R.; Lundgren, Edvin; Weaver, Jason F.

doi:10.1021/acs.jpcc.6b09908

Cited by 12 publications

(9 citation statements)

References 48 publications

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“…This type of basic information is necessary to optimize the performance of catalysts utilized to facilitate the CO 2 → CH 3 OH transformation. The chemical reactivity of methanol, as the simplest carbon-containing alcohol, has garnered considerable attention related to the transformation of C–H and C–OH bonds on surfaces of metals, − oxides, − and mixed oxides or more complex materials. − In this work, we study the dynamic interaction of methanol with ZnO/Cu 2 O/Cu(111) catalysts employing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), scanning tunneling microscopy (STM), and calculations based on density functional theory (DFT). Preferential adsorption is observed on the ZnO regions of the catalysts, with the adsorbate undergoing desorption as CH 3 OH or full decomposition (CH 3 O → CH 2 O → CHO → CO).…”

Section: Introductionmentioning

confidence: 99%

Understanding Methanol Synthesis on Inverse ZnO/CuO_x/Cu Catalysts: Stability of CH₃O Species and Dynamic Nature of the Surface

et al. 2021

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Inverse ZnO/Cu catalysts are key systems in the conversion of CO 2 , a common atmospheric pollutant, into methanol, a high-value chemical and fuel. The chemistry of methanol and methoxy groups over inverse ZnO/Cu 2 O/Cu(111) catalysts was investigated employing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), scanning tunneling microscopy (STM), and calculations based on density functional theory (DFT). The results of AP-XPS show that the adsorption of methanol on the binary oxide substrate at 300 K leads to formation of *CH 3 O and *HCOO species with a minor amount of *CH x . Most of the methoxy groups disappeared from the surface after heating to 450 K, the onset temperature for the formation of methanol during the hydrogenation of CO 2 . The results of AP-XPS, STM, and DFT point to preferential adsorption of methoxy on the ZnO regions of the binary oxide. On the supported ZnO or on a ZnO−Cu 2 O interface, the breaking of the O−H bond in methanol is an exothermic process with a negligible (1−2 kcal/mol) or non-existent energy barrier depending on the size and shape of the ZnO islands. STM shows large changes in the morphology of ZnO/Cu 2 O/Cu(111) surfaces upon reaction with methanol. The produced *CH 3 O, *HCOO, and *CH x species are localized in groups of active sites that have a dynamic nature and their structure changes during the adsorption/desorption processes.

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Section: Introductionmentioning

confidence: 99%

Understanding Methanol Synthesis on Inverse ZnO/CuO_x/Cu Catalysts: Stability of CH₃O Species and Dynamic Nature of the Surface

et al. 2021

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“…More recently, it has been proposed as the cornerstone of future technologies in what is referred to as the “methanol economy” due to its relatively high energy density and propensity toward chemical transformations. The chemical reactivity of methanol, as the simplest carbon containing alcohol, has garnered considerable attention related to the transformation of C–H and C–OH bonds on surfaces of metals, − oxides, − and more complex surfaces. − Copper and its oxides are used extensively in chemical processes involving methanol as varied as methanol oxidation − ( ), methanol steam reforming , (CH 3 OH + H 2 O → CO 2 + 3H 2 ), and even the synthesis of methanol − ( ; ; ) due to the exceedingly favorable performance/cost compared to other transition metals, such as Pd or Pt. In all such reactions, the fate of the methoxy surface intermediate (CH 3 O−) dictates the first interaction of the methanol molecule with the first layer of atoms of the surface.…”

Section: Introductionmentioning

confidence: 99%

In Situ Studies of Methanol Decomposition Over Cu(111) and Cu₂O/Cu(111): Effects of Reactant Pressure, Surface Morphology, and Hot Spots of Active Sites

et al. 2020

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The dissociative adsorption of methanol was investigated on Cu(111) and ultrathin Cu 2 O films. We employed synchrotron-based Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Scanning Tunneling Microscopy (STM) to study the dynamics of gas−solid interactions, and calculations based on Density Functional Theory (DFT) were used to examine the reaction path. C 1s XPS spectra revealed that methanol underwent dissociative adsorption on plain Cu(111) to form methoxy (CH 3 O), formaldehyde (H 2 CO), and formate (HCOO) at a pressure range of 0.5−10 mTorr, with these species remaining on the surface after evacuation. This was accompanied by the appearance of a low coverage (∼0.05 ML) of O ads in the O 1s which can be considered a highly active site for methanol activation. The high activity is apparent by a coverage of 0.8 ML of methoxy at room temperature. STM was unable to image these species at room temperature as they were highly mobile on metallic copper. In contrast, for CH 3 OH on Cu 2 O/Cu(111), STM showed clear hot spots for reaction and a complex array of adsorption structures. On the oxide substrate, there was decomposition of methanol to H 2 CO, CH 3 O, HCOO, and hydrocarbon species (CH x ) due to the subsequent interactions of methanol with lattice oxygen. Cu(111) remained entirely saturated with decomposition products under 10 mTorr of methanol (θ ≈ 0.97 ML), whereas the Cu 2 O overlayer was saturated at a much lower coverage (θ ≈ 0.30 ML). STM revealed rows and step edges of Cu 2 O decorated with decomposition products and metallic Cu islands ∼5 nm in size. The difference in activity between Cu(111) and Cu 2 O/ Cu(111) is attributed to the significant amount of O present on the oxide surface. Density Functional theory (DFT) calculations described the XPS measurements well, showing a likely methanol dissociation to *CH 3 O and therefore a surface reduction. More importantly, the DFT results revealed that it was the chemisorbed oxygen on Cu 2 O/Cu(111) which oxidized the dissociated *CH 3 O to *HCOO and eventually CO 2 , while the reaction only involving upper oxygen on the Cu 2 O hexagonal ring led to the formation of H 2 CO.

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“…TbO x films provide a particularly interesting avenue in which to broaden this understanding as they share structural and oxidative similarities with CeO x . , Though TbO x films are expected to follow similar oxidation pathways as observed with CeO x because of similarity in achievable oxidation states, TbO 2 is more easily reduced than CeO 2 and may exhibit different chemical properties stemming from dissimilar affinity for the 4+ oxidation state. Prior research has shown that unlike CeO x , TbO x deposited on Pt(111) in UHV under slight O 2 pressures (<10 –6 Torr) stabilizes as Tb 2 O 3 (111) and can then be further oxidized to TbO 2 via exposure to atomic oxygen. , Reactivity experiments have also shown that TbO 2 is more selective in promoting the partial oxidation of methanol to formaldehyde compared with CeO 2 . , …”

Section: Introductionmentioning

confidence: 99%

“…20,21 Reactivity experiments have also shown that TbO 2 is more selective in promoting the partial oxidation of methanol to formaldehyde compared with CeO 2 . 17,22 In the present study, we investigated the growth of Tb…”

Section: ■ Introductionmentioning

confidence: 99%

Growth and Structure of Tb₂O₃(111) Films on Pt(111)

2018

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We investigated the formation and structure of Tb 2 O 3 (111) thin films grown on Pt(111) using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We find that the Tb 2 O 3 (111) films adopt an oxygen-deficient cubic fluorite structure, wherein the Tb cations form an approximately (1.32 × 1.32) lattice in registry with the Pt(111) substrate. STM shows that terbia film growth follows the Stranski−Krastanov mechanism, in which Tb 2 O 3 (111) initially forms a well-connected wetting layer up to a Tb 2 O 3 coverage of ∼2 ML (monolayer), whereas multilayer Tb 2 O 3 islands develop as the coverage increases thereafter. The Tb 2 O 3 (111) wetting layer yields a sharp (3 × 3) LEED pattern relative to the primary Tb spots that we attribute to diffraction from a 3/4 coincidence lattice formed at the Tb 2 O 3 (111)−Pt(111) interface. STM further shows that oxygen vacancies are randomly distributed within the lattice of the Tb 2 O 3 (111) wetting layer. The (3 × 3) LEED pattern diminishes during the transition to island growth but re-emerges as the islands ripen at Tb 2 O 3 coverages beyond about 5 ML. We attribute the re-emergent LEED pattern to a (3 × 3) superstructure of oxygen vacancies within the Tb 2 O 3 (111) islands, the formation of which is likely mediated by the (3 × 3) Tb 2 O 3 −Pt(111) coincidence lattice. The (3 × 3) structure persists to Tb 2 O 3 coverages of at least 10 ML and remains stable after annealing to temperatures up to 1100 K. An implication of this study is that Tb 2 O 3 (111) surfaces with well-defined, ordered oxygen vacancies can be stabilized to better study the role of structure and oxygen vacancies on the chemical reactivity of TbO x surfaces.

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Methanol Adsorption and Oxidation on Reduced and Oxidized TbO_x(111) Surfaces

Cited by 12 publications

References 48 publications

Understanding Methanol Synthesis on Inverse ZnO/CuO_x/Cu Catalysts: Stability of CH₃O Species and Dynamic Nature of the Surface

Understanding Methanol Synthesis on Inverse ZnO/CuO_x/Cu Catalysts: Stability of CH₃O Species and Dynamic Nature of the Surface

In Situ Studies of Methanol Decomposition Over Cu(111) and Cu₂O/Cu(111): Effects of Reactant Pressure, Surface Morphology, and Hot Spots of Active Sites

Growth and Structure of Tb₂O₃(111) Films on Pt(111)

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Methanol Adsorption and Oxidation on Reduced and Oxidized TbOx(111) Surfaces

Cited by 12 publications

References 48 publications

Understanding Methanol Synthesis on Inverse ZnO/CuOx/Cu Catalysts: Stability of CH3O Species and Dynamic Nature of the Surface

Understanding Methanol Synthesis on Inverse ZnO/CuOx/Cu Catalysts: Stability of CH3O Species and Dynamic Nature of the Surface

In Situ Studies of Methanol Decomposition Over Cu(111) and Cu2O/Cu(111): Effects of Reactant Pressure, Surface Morphology, and Hot Spots of Active Sites

Growth and Structure of Tb2O3(111) Films on Pt(111)

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Methanol Adsorption and Oxidation on Reduced and Oxidized TbO_x(111) Surfaces

Understanding Methanol Synthesis on Inverse ZnO/CuO_x/Cu Catalysts: Stability of CH₃O Species and Dynamic Nature of the Surface

Understanding Methanol Synthesis on Inverse ZnO/CuO_x/Cu Catalysts: Stability of CH₃O Species and Dynamic Nature of the Surface

In Situ Studies of Methanol Decomposition Over Cu(111) and Cu₂O/Cu(111): Effects of Reactant Pressure, Surface Morphology, and Hot Spots of Active Sites

Growth and Structure of Tb₂O₃(111) Films on Pt(111)