| 1. |
- Baber, Ashleigh E., et al.
(author)
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In Situ Imaging of Cu2O under Reducing Conditions : Formation of Metallic Fronts by Mass Transfer
- 2013
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 135:45, s. 16781-16784
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Journal article (peer-reviewed)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 allows 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.
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| 2. |
- Baber, Ashleigh E., et al.
(author)
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Stabilization of Catalytically Active Cu plus Surface Sites on TitaniumCopper Mixed-Oxide Films**
- 2014
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In: Angewandte Chemie International Edition. - : Gesellschaft Deutscher Chemiker. - 1433-7851 .- 1521-3773. ; 53:21, s. 5336-5340
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Journal article (peer-reviewed)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.
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| 3. |
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| 4. |
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| 5. |
- Wang, Chunlei, et al.
(author)
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Stabilization of Cu2O through Site-Selective Formation of a Co1Cu Hybrid Single-Atom Catalyst
- 2022
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:5, s. 2313-2320
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Journal article (peer-reviewed)abstract
- Single-atom catalysts (SACs) consist of a low coverage of isolated metal atoms dispersed on a metal substrate, called single-atom alloys (SAAs), or alternatively single metal atoms coordinated to oxygen atoms on an oxide support. We present the synthesis of a new type of Co1Cu SAC centers on a Cu2O(111) support by means of a site-selective atomic layer deposition technique. Isolated metallic Co atoms selectively coordinate to the native oxygen vacancy sites (Cu sites) of the reconstructed Cu2O(111) surface, forming a Co1Cu SAA with no direct Co- Ox bonds. The centers, here referred to as Co1Cu hybrid SACs, are found to stabilize the active Cu+ sites of the low-cost Cu2O catalyst that otherwise is prone to deactivation under reaction conditions. The stability of the Cu2O(111) surface was investigated by synchrotron radiation-based ambient-pressure X-ray photoelectron spectroscopy under reducing CO environment. The structure and reduction reaction are modeled by density functional theory calculations, in good agreement with experimental results.
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| 6. |
- Xu, Fang, et al.
(author)
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Redox-Mediated Reconstruction of Copper during Carbon Monoxide Oxidation
- 2014
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:29, s. 15902-15909
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Journal article (peer-reviewed)abstract
- Copper has excellent initial activity for the oxidation of CO, yet it rapidly deactivates under reaction conditions. In an effort to obtain a full picture of the dynamic morphological and chemical changes occurring on the surface of catalysts under CO oxidation conditions, a complementary set of in situ ambient pressure (AP) techniques that include scanning tunneling microscopy, infrared reflection absorption spectroscopy (IRRAS), and X-ray photoelectron spectroscopy were conducted. Herein, we report in situ AP CO oxidation experiments over Cu(111) model catalysts at room temperature. Depending on the CO:O-2 ratio, Cu presents different oxidation states, leading to the coexistence of several phases. During CO oxidation, a redox cycle is observed on the substrate's surface, in which Cu atoms are oxidized and pulled from terraces and step edges and then are reduced and rejoin nearby step edges. IRRAS results confirm the presence of under-coordinated Cu atoms during the reaction. By using control experiments to isolate individual phases, it is shown that the rate for CO oxidation decreases systematically as metallic copper is fully oxidized.
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