Dario Stacchiola

Brookhaven National Laboratory, New York City, New York, United States

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Publications (109)594.93 Total impact

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    ABSTRACT: Adsorbate-driven morphological changes of pitted-Cu(111) surfaces have been investigated following the adsorption and desorption of CO and H. The morphology of the pitted-Cu(111) surfaces, prepared by Ar+ sputtering, exposed a few atomic layers deep nested hexagonal pits of diameters from 8 to 38 nm with steep step bundles. The roughness of pitted-Cu(111) surfaces can be healed by heating to 450-500 K in vacuum. Adsorption of CO on the pitted-Cu(111) surface leads to two infrared peaks at 2089-2090 and 2101-2105 cm-1 for CO adsorbed on under-coordinated sites in addition to the peak at 2071 cm-1 for CO adsorbed on atop sites of the close-packed Cu(111) surface. CO adsorbed on under-coordinated sites is thermally more stable than that of atop Cu(111) sites. Annealing of the CO-covered surface from 100 to 300 K leads to minor changes of the surface morphology. In contrast, annealing of a H covered surface to 300 K creates a smooth Cu(111) surface as deduced from infrared data of adsorbed CO and scanning tunneling microscopy (STM) imaging. The observation of significant adsorbate-driven morphological changes with H is attributed to its stronger modification of the Cu(111) surface by the formation of a sub-surface hydride with a hexagonal structure, which relaxes into the healed Cu(111) surface upon hydrogen desorption. These morphological changes occur ~ 150 K below the temperature required for healing of the pitted-Cu(111) surface by annealing in vacuum. In contrast, the adsorption of CO, which only interacts with the top-most Cu layer and desorbs by 160 K, does not significantly change the morphology of the pitted-Cu(111) surface.
    Physical Chemistry Chemical Physics 12/2014; · 4.20 Impact Factor
  • Catalysis Today 11/2014; · 3.31 Impact Factor
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    ABSTRACT: doi: 10.1021/jp507966v
    The Journal of Physical Chemistry C 10/2014; · 4.84 Impact Factor
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    ABSTRACT: The transformation of CO2 into alcohols or other hydrocarbon compounds is challenging because of the difficulties associated with the chemical activation of CO2 by heterogeneous catalysts. Pure metals and bimetallic systems used for this task usually have low catalytic activity. Here we present experimental and theoretical evidence for a completely different type of site for CO2 activation: a copper-ceria interface that is highly efficient for the synthesis of methanol. The combination of metal and oxide sites in the copper-ceria interface affords complementary chemical properties that lead to special reaction pathways for the CO2→CH3OH conversion.
    Science 08/2014; 345(6196):546-50. · 31.48 Impact Factor
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    ABSTRACT: Understanding the mechanisms governing chemical and morphological changes induced by an ambient-pressure gas and how such changes influence the activity of heterogeneous catalysts is central to the formation of a predictive capability for structure–reactivity relationships. With techniques such as ambient-pressure photoelectron spectroscopy, scanning tunneling microscopy, and surface X-ray diffraction, active phases and reaction intermediates can be probed in situ on relevant samples to form a comprehensive picture of this dynamic interplay between gases and surfaces. Of particular interest is the interaction of oxygen and carbon monoxide with catalysts. We will describe how model systems of increased complexity can be used to investigate gas-mediated mass transfer processes that may occur even at relatively modest temperatures. Furthermore, we will discuss how the morphology may be tailored to study specific contributions from defect sites and charge transfer to catalytic activity.
    The Chemical Record 08/2014; 14(5). · 5.58 Impact Factor
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    ABSTRACT: Abstract Molybdenum carbide catalysts, including both α-MoC1-x (x y (y ≈ 0.5), were synthesized by thermal treatment of hexagonal molybdenum oxide (HMO) with mixtures of hydrogen and methane/ethane. In situ X-ray diffraction was used to follow the carburization processes. It was found that a high carbon concentration in the reactant gases favors the formation of α-MoC1-x while a low concentration favors β-MoCy. Moreover, a lower concentration of carbon is needed to form α-MoC1-x when using ethane instead of methane as the carburization agent. It was also found that the transformation path from HMO to α-MoC1-x is dependent on the heating procedure. Baking HMO at 400 °C in hydrogen for several hours leads to the formation of Mo oxyhydride, which can be further carburized to α-MoC1-x at a temperature as low as 450 °C with 20 % ethane. Catalytic tests indicate that α-MoC1-x and β-MoCy are both active as catalysts for the hydrogenation of CO2, but the overall activity and selectivity towards CO, CH4 and CH3OH production is strongly affected by the Mo/C ratio in the carbide. β-MoCy is more active than α-MoC1-x for the conversion of CO2 and produces mainly methane and CO as reaction products. On the other hand, α-MoC1-x is less active but more selective for methanol production. Graphical Abstract
    Catalysis Letters 08/2014; 144(8):1418-1424. · 2.29 Impact Factor
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    ABSTRACT: Abstract Formate species have been proposed to be either critical intermediates or spectators in the water–gas shift (WGS) and methanol synthesis processes. CeOx–CuyO/Cu(1 1 1) has been shown to be a very active inverse catalyst for the WGS reaction. We present here the study of formate species obtained from the deprotonation of formic acid (HCOOH) on the inverse catalysts. Exposure of CeOx–CuyO/Cu(1 1 1) to HCOOH at 300 K leads to the formation of formates on both ceria and Cu sites. The formates isolated on CeOx–CuyO/Cu(1 1 1) systems cannot be hydrogenated even at a pressure of 200 Torr H2 at 300–350 K. The formate species localized on ceria sites are thermally more stable than those on Cu sites, and the thermal decomposition of all of the formates occurs by dehydrogenation releasing CO2 and H2. Evidence of reverse spillover of formates from the oxide to the metal was observed on CeO2−x/Cu(1 1 1) inverse catalysts.
    Catalysis Today 07/2014; · 3.31 Impact Factor
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    ABSTRACT: The reducibility of metal oxides is of great importance to their catalytic behavior. Herein, we combined ambient-pressure scanning tunneling microscopy (AP–STM), X-ray photoemission spectroscopy (AP–XPS), and DFT calculations to study the CO titration of CuxO thin films supported on Cu(1 1 1) (CuxO/Cu(1 1 1)) aiming to gain a better understanding of the roles that the Cu(1 1 1) support and surface defects play in tuning catalytic performances. Different conformations have been observed during the reduction, namely, the 44 structure and a recently identified (5–7–7–5) Stone–Wales defects (5–7 structure). The DFT calculations revealed that the Cu(1 1 1) support is important to the reducibility of supported CuxO thin films. Compared with the case for the Cu2O(1 1 1) bulk surface, at the initial stage CO titration is less favorable on both the 44 and 5–7 structures. The strong CuxOCu interaction accompanied with the charge transfer from Cu to CuxO is able to stabilize the oxide film and hinder the removal of O. However, with the formation of more oxygen vacancies, the binding between CuxO and Cu(1 1 1) is weakened and the oxide film is destabilized, and Cu2O(1 1 1) is likely to become the most stable system under the reaction conditions. In addition, the surface defects also play an essential role. With the proceeding of the CO titration reaction, the 5–7 structure displays the highest activity among all three systems. Stone–Wales defects on the surface of the 5–7 structure exhibit a large difference from the 44 structure and Cu2O(1 1 1) in CO binding energy, stability of lattice oxygen, and, therefore, the reduction activity. The DFT results agree well with the experimental measurements, demonstrating that by adopting the unique conformation, the 5–7 structure is the active phase of CuxO, which is able to facilitate the redox reaction and the Cu2O/Cu(1 1 1)Cu transition.
    ChemCatChem 06/2014; · 5.18 Impact Factor
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    ABSTRACT: Reducible oxides have been shown to greatly improve the activity of water gas shift (WGS) catalysts. The precise mechanism for this effect is a matter of intense debate, but the dissociation of water is generally considered to be the key step in the reaction. We present here a study of the water activation on oxygen vacancies at the support as part of the mechanism of the WGS reaction on Pt supported on pure and gallium-doped ceria. Doping the ceria with gallium allows tuning the vacancies in the support while maintaining constant the metal dispersion. An inverse relationship was found between the catalytic activity to WGS and the amount of oxygen vacancies. In situ time-resolved X-ray diffraction, mass spectrometry, and diffuse reflectance infrared spectroscopy (DRIFT) showed that the oxygen vacancy filling by water is always fast in either Pt/CeO2 or Pt/CeGa. DFT calculation provides molecular insights to understand the pathway of water reaction with vacancies at the metal–oxide interface sites. Our results suggest that the activation of the water molecule in the WGS mechanism is not the rate-limiting step in these systems. Concentration-modulation spectroscopy in DRIFT mode under WGS reaction conditions allows the selective detection of key reaction intermediates, a monodentate formate (HCOO) and carboxylate (CO2δ−) species, which suggests the prevalence of a carboxyl (HOCO) mechanism activated at the oxide–metal interface of the catalyst.
    ACS Catalysis 05/2014; 4(6):2088–2096. · 7.57 Impact Factor
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    ABSTRACT: doi: 10.1021/cs500148e
    ACS Catalysis 04/2014; · 7.57 Impact Factor
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    ABSTRACT: The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper-based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu+ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed-metal oxide with a Cu+ terminated surface that is highly active for CO oxidation.
    Angewandte Chemie 04/2014; 126(21).
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    ABSTRACT: The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper-based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu+ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed-metal oxide with a Cu+ terminated surface that is highly active for CO oxidation.
    Angewandte Chemie International Edition 04/2014; 53(21). · 11.34 Impact Factor
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    ABSTRACT: The activation of gold in catalytic reactions has been the subject of intensive research that has led to the transformation of one of the least chemically reactive elements to a catalyst with excellent activity and selectivity. Scientists have performed numerous systematic experimental and theoretical studies using model systems, which have explained the role of Au in chemical reactions with progressively increasing degrees of structural and chemical complexity. We present an overview of recent studies of model Au(111), CeOx/Au(111), and Au/CeOx/TiO2(110) surfaces that use Au in different structural configurations specifically for the water-gas shift reaction (WGS, CO + H2O → CO2 + H2), an important industrial process for the purification of CO. We demonstrate the significance of key structural components of the Au-based supported catalysts such as the metal-oxide interface (Au-Ox) toward the WGS catalytic activity, a "structure-activity" relationship. In the WGS reaction, Au(111) or Au nanoparticles have poor catalytic performance due to their inability to activate one of the most important steps of the reaction, the breaking of O-H bonds in the dissociation of water (H2O → OH + H). The relatively large energetic barrier can be overcome by using O on Au(111) to facilitate the formation of OH at low temperatures, with eventual CO2 and H2 production upon reaction between CO and the adsorbed OH. However, the inability to replace the reacted O prevents a sustainable catalytic process from occurring on Au(111). The addition of a small concentration of CeOx nanoparticles on top of the Au(111) surface facilitates this rate-determining step and easily continues the catalytic cycle in the production of H2. We have discovered that CeOx nanoparticles in contact with Au(111) are rich in Ce(3+). They also have a distinct metal-oxide interface, which sustains excellent activity for the WGS reaction via the formation of a unique carboxylate intermediate, making CeOx/Au(111) more active than Cu/ZnO(0001̅), Cu(100), and Cu(111) which are the typical catalysts for this reaction. Taking this knowledge one step further, bringing these components (oxide and metal nanoparticles) together over a second oxide in Au/CeOx/TiO2 produces a system with unique morphological and electronic properties. The result is a superior catalyst for the WGS reaction, both as a model system (Au/CeOx/TiO2(110)) and as powder material (Au/CeOx/TiO2(anatase)) optimized directly in a series of systematic investigations.
    Accounts of Chemical Research 11/2013; · 24.35 Impact Factor
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    ABSTRACT: The electronic properties of Ni and Pt nanoparticles deposited on CeO2(111) have been examined using core and valence photoemission. The results of valence photoemission point to a new type of metal–support interaction which produces large electronic perturbations for small Ni and Pt particles in contact with ceria. The Ni/CeO2(111) and Pt/CeO2(111) systems exhibited a density of metal d states near the Fermi level that was much smaller than that expected for bulk metallic Ni or Pt. The electronic perturbations induced by ceria on Ni made this metal a very poor catalyst for CO methanation, but transformed Ni into an excellent catalyst for the production of hydrogen through the water-gas shift and the steam reforming of ethanol. Furthermore, the large electronic perturbations seen for small Pt particles in contact with ceria significantly enhanced the ability of the admetal to adsorb and dissociate water made it a highly active catalyst for the water-gas shift. The behaviour seen for the Ni/CeO2(111) and Pt/CeO2(111) systems illustrates the positive effects derived from electronic metal–support interactions and points to a promising approach for improving or optimizing the performance of metal/oxide catalysts.
    Topics in Catalysis 11/2013; · 2.22 Impact Factor
  • 224th ECS Meeting; 10/2013
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    ABSTRACT: Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of in situ microscopy and spectroscopy techniques that in the presence of reactants, an oxide catalyst's chemical state and morphology are dynamically modified. The reduction of Cu2O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allow us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution in situ imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces.
    Journal of the American Chemical Society 10/2013; · 11.44 Impact Factor
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    ABSTRACT: Ceria based catalysts show remarkable activity for CO conversion reactions such as CO oxidation and the water-gas shift reaction. The identification of adsorption sites on the catalyst surfaces is essential to understand the reaction mechanisms of these reactions, but the complexity of heterogeneous powder catalysts and the propensity of ceria to easily change oxidation states in the presence of small concentrations of either oxidizing or reducing agents make the process difficult. In this study, the adsorption of CO on CuOx/Cu(111) and CeOx/Cu(111) systems has been studied using infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. IR peaks for the adsorbed CO on O/Cu(111) with only chemisorbed oxygen, well-ordered Cu2O/Cu(111) and disordered copper oxide [CuOx/Cu(111)] were observed at 2070-2072, 2097-2098 and 2101-2111 cm(-1), respectively. On CeOx/Cu(111) systems CO chemisorbs at 90 K only on Cu sites under ultra-high vacuum (UHV) conditions, whereas at elevated CO pressures and low temperatures adsorption of CO on Ce(3+) is observed, with a corresponding IR peak at 2162 cm(-1). These experimental results are further supported by DFT calculations, and help to unequivocally distinguish the presence of Ce(3+) cations on catalyst samples by using CO as a probe molecule.
    Physical Chemistry Chemical Physics 08/2013; · 4.20 Impact Factor
  • ChemInform 08/2013; 44(33).
  • Hui Wang, Kai Sun, Franklin Tao, Dario J Stacchiola, Yun Hang Hu
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    ABSTRACT: A useful Li: A simple reaction between Li2 O and CO, gives a new type of three-dimensional graphene sheets-honeycomb structured graphene. A dye-sensitized solar cell (DSSC) with the new graphene counter electrode has an energy conversion efficiency as high as 7.8 %, which is comparable to that of DSSCs with an expensive Pt counter electrode.
    Angewandte Chemie International Edition 07/2013; · 11.34 Impact Factor
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    ABSTRACT: The interaction of atomic hydrogen with the Cu(111) surface was studied by a combined experimental-theoretical approach, using infrared reflection absorption spectroscopy, temperature programmed desorption, and density functional theory (DFT). Adsorption of atomic hydrogen at 160 K is characterized by an anti-absorption mode at 754 cm(-1) and a broadband absorption in the IRRA spectra, related to adsorption of hydrogen on three-fold hollow surface sites and sub-surface sites, and the appearance of a sharp vibrational band at 1151 cm(-1) at high coverage, which is also associated with hydrogen adsorption on the surface. Annealing the hydrogen covered surface up to 200 K results in the disappearance of this vibrational band. Thermal desorption is characterized by a single feature at ∼295 K, with the leading edge at ∼250 K. The disappearance of the sharp Cu-H vibrational band suggests that with increasing temperature the surface hydrogen migrates to sub-surface sites prior to desorption from the surface. The presence of sub-surface hydrogen after annealing to 200 K is further demonstrated by using CO as a surface probe. Changes in the Cu-H vibration intensity are observed when cooling the adsorbed hydrogen at 180 K to 110 K, implying the migration of hydrogen. DFT calculations show that the most stable position for hydrogen adsorption on Cu(111) is on hollow surface sites, but that hydrogen can be trapped in the second sub-surface layer.
    The Journal of Chemical Physics 07/2013; 139(4):044712. · 3.12 Impact Factor

Publication Stats

2k Citations
594.93 Total Impact Points

Institutions

  • 2009–2014
    • Brookhaven National Laboratory
      • Chemistry Department
      New York City, New York, United States
  • 2009–2010
    • Michigan Technological University
      • • Department of Chemistry
      • • Department of Materials Science & Engineering
      Houghton, Michigan, United States
  • 1999–2010
    • University of Wisconsin - Milwaukee
      • • Department of Chemistry and Biochemistry
      • • Laboratory for Surface Studies
      Milwaukee, WI, United States
  • 2006–2009
    • Fritz Haber Institute of the Max Planck Society
      • Department of Physical Chemistry
      Berlin, Land Berlin, Germany
  • 2008
    • Max Planck Society
      München, Bavaria, Germany
  • 2007
    • Humboldt-Universität zu Berlin
      • Department of Chemistry
      Berlin, Land Berlin, Germany
  • 2000
    • Universidad Nacional de San Luis
      • Department of Physics
      San Luis, San Luis, Argentina