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Tang Y.,Henan Normal University | Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Dai X.,Henan Normal University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2013

The geometry, electronic structure, and catalytic properties of Pt catalyst supported on the nonmetal doped-graphene (denoted as D-graphene, where D represents the B, Si, O and P dopant) substrates are investigated using the first-principles method. The nonmetal atoms (NA) have small adsorption energies and prefer to be adsorbed at the bridge site on the pristine graphene. In contrast, they prefer to be anchored at the vacancy site as dopants and form stable D-graphene. The NA dopants can modify the local surface curvature and the electronic properties of graphene and therefore regulate the chemical activity of the D-graphene, which can be used as support for catalysts. The highly stable Pt catalysts supported on the D-graphene substrates (Pt/D-graphene) exhibit good catalytic activity for CO oxidation. By comparing both the Langmuir-Hinshelwood (LH) and Eley-Rideal reaction mechanisms, the LH reaction as the starting state is energetically more favorable. Among the Pt/D-graphene systems studied, CO oxidation reactions are more prone to take place with lower energy barriers on the Pt/Si-graphene. The results provide valuable guidance on selecting dopants in graphene to fabricate carbon-based catalysts for CO oxidation, and validate the reactivity of single-atom catalyst for the designing the atomic-scale catalysts. © 2013 American Chemical Society.


Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Wang Q.,Henan Normal University | Wei S.,Henan Normal University | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

The interaction of a water molecule with the (111) surfaces of stoichiometric and reduced ceria is investigated using first principle density functional theory with the inclusion of the on-site Coulomb interaction (DFT+U). It is found that on the stoichiometric ceria(111) surface, the water molecule is adsorbed spontaneously through single hydrogen bond configuration. In contrast, on the lightly reduced ceria(111), there exist both molecular adsorption (no-H-bond configuration) and dissociative adsorption (surface hydroxyl) modes. It is obvious that oxygen vacancies can enhance the interaction of water with the substrate. Phase diagrams for stoichiometric and reduced ceria(111) surfaces in equilibrium with water vapor in the complete range of experimentally accessible gas phase condition are calculated and discussed combining the DFT results and thermodynamics data using the ab initio atomistic thermodynamic method. We present a detailed analysis of the stability of the water-ceria system as a function of the ambient conditions, and focus on two important surface processes for water adsorption on the stoichiometric and on the lightly reduced surfaces, respectively. © 2010 American Chemical Society.


Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Xie L.,Henan Normal University | Ma D.,Fudan University | And 2 more authors.
Journal of Physical Chemistry C | Year: 2011

Ceria-supported copper is a wonderful catalyst for the water-gas shift (WGS) reaction which has been demonstrated experimentally. Using first-principles calculations based on density functional theory (DFT), we identify the mechanisms for the growth of small Cu clusters (Cux, x = 1-4) on ceria and the dissociation of H2O on the Cu 4/CeO2 catalyst. Our calculations indicate that the strong copper-oxygen interaction at the Cu4/CeO2 interface is comparable to the copper-copper intracluster interactions, and the competitions between them determine the morphologies of Cu clusters on ceria. H2O dissociates with small barriers (0.19-0.31 eV) on the Cu4/CeO 2 catalyst, and the highly catalytic activity originates from the enhanced electrostatic interaction between the positively charged Cu sites and the polar H2O molecule. The Cu/O interface sites of the ceria-supported copper catalyst are identified as the active sites for H 2O dissociation. As a buffer to accept/release electrons, the ceria support not only activates the Cu sites but also participates in the H 2O dissociation reaction at the Cu/O interface. © 2011 American Chemical Society.


Tang Y.,Henan Normal University | Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Dai X.,Henan Normal University | Dai X.,Henan Key Laboratory of Photovoltaic Materials
Physical Chemistry Chemical Physics | Year: 2012

The catalytic oxidation of CO on Pt/X-graphene (X = "pri" for pristine- or "SV" for defective-graphene with a single vacancy) is investigated using the first-principles method based on density functional theory. In contrast to a Pt atom on pristine graphene, a vacancy defect in graphene strongly stabilizes a single Pt adatom and makes the Pt adatom more positively charged, which helps to weaken the CO adsorption and facilitates the O 2 adsorption, thus enhancing the activity for CO oxidation and alleviating the CO poisoning of the platinum catalysts. The CO oxidation reaction on Pt/SV-graphene has a low energy barrier (0.58 eV) by the Langmuir-Hinshelwood (LH) reaction (CO + O 2 → OOCO → CO 2 + O ads) which is followed by the Eley-Rideal (ER) reaction with an energy barrier of 0.59 eV (CO + O ads → CO 2). The results validate the reactivity of catalysts on the atomic-scale and initiate a clue for fabricating carbon-based catalysts with low cost and high activity. © 2012 the Owner Societies.


Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Wang Q.,Henan Normal University | Wei S.,Henan Normal University
Physical Chemistry Chemical Physics | Year: 2011

The interaction of water molecules with the Cu-CeO2(111) catalyst (Cu/CeO2 and Cu0.08Ce0.92O 2) is studied systematically by using the DFT+U method. Although both molecular and dissociative adsorption states of water are observed on all the considered Cu-CeO2(111) systems, the dissociation is preferable thermodynamically. Furthermore, the dissociation of water molecule relates to the geometric structure (e.g. whether or not there are oxygen vacancies; whether or not the reduced substrate retains a fluorite structure) and the electronic structure (e.g. whether or not there is reduced cerium, Ce3+) of the substrate. In addition, the adsorption of water molecules induces variations of the electronic structure of the substrate, especially for Cu/CeO 2-x(111)-B (a Cu atom adsorbed symmetrically above the vacancy of the reduced ceria) and highly reduced Cu0.08Ce0.92O 2(111), i.e. the Cu0.08Ce0.92O 2-x(111)-h. The variations of electronic structure promote the dissociation of water for the highly reduced system Cu0.08Ce 0.92O2-x(111)-h. More importantly, the improvement of WGS reaction by Cu-ceria is expected to be by the associative route through different intermediates. © 2011 the Owner Societies.


Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | He B.,Henan Normal University | Lu Z.,Henan Normal University | Hermansson K.,Uppsala University
Journal of Physical Chemistry C | Year: 2010

With the use of the DFT+U method, the properties of Cu adsorbed on the stoichiometric CeO2(111) surface, Cu-doped CeO2(111) (denoted as Cu0.08Ce0.92O2) surface, and CO oxidation on the stoichiometric Cu0.08Ce0.92O2 surface are studied systematically. It is found that (i) Cu is stable both as an adsorbed atom on the surface and as dopant in the surface region. Cu adsorbed at the surface is Cu(+I) while Cu as a dopant atom is Cu(+II). (ii) The Cu dopant facilitates O-vacancy formation considerably, while Cu adsorption on the stoichiometric CeO2(111) surface may suppress oxygen vacancy formation. (iii) Physisorbed CO, physisorbed CO2, as well as chemisorbed CO (carbonate) species are observed on the Cu-doped CeO 2(111) surface, in contrast, on the clean ceria(111) surface, only physisorbed CO was previously observed. C-O distances, adsorption energies, and surface-induced C-O vibrational frequency shifts were used to characterize these species. © 2010 American Chemical Society.


Lu Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials
Journal of Physics Condensed Matter | Year: 2010

Results from first principles calculations present a rather clear atomic and electronic level picture of the interaction of single noble metals (NM: Pd, Pt and Rh) and the corresponding NM4 clusters with a CeO 2(111) surface. The most preferable adsorption sites for both the Pd and Pt adatoms are the surface O-bridge sites, while the Rh adatom prefers to stay at the O-hollow site. The Rh adatom shows much stronger interaction with the CeO2(111) surface than the Pd and Pt adatoms do, while the Pd adatom has the smallest adsorption energy. The dependence of the Rh/ceria interfacial properties on the value of the Hubbard U-term was tested systematically. The small clusters show stronger interaction than the corresponding single NM adatoms on the CeO2(111) surface. The reaction of NM + Ce4+ → NMδ+/Ce3+ was found for both the single NM adatoms and the small cluster adsorbate, indicating that NM adsorbates were mainly oxidized by the surface Ce ions with obvious charge transfer from NM to the CeO2(111) surface. The three base atoms of the small clusters that bonded with the CeO2(111) surface showed positive charges, while the top metal atoms of the NM4 clusters had a small negative charge. © 2010 IOP Publishing Ltd.


Tang Y.,Henan Normal University | Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Dai X.,Henan Normal University | Dai X.,Henan Key Laboratory of Photovoltaic Materials
Journal of Nanoparticle Research | Year: 2012

Adsorption energies and stable configurations of CO on the Pt clusters are investigated using the first-principles density-functional theory method. It is found that the adsorption of CO on the top site of the Pt 4 cluster is more stable than that on the bridge site. The atomic charges are unevenly distributed within the charged Pt4 cluster, and the structural positions of the Pt atoms determine their charge states and therefore their activity. A systematic study on the effects of electrons and holes doping in the Pt4 clusters suggest an effective method to prevent the CO poisoning through regulating the total charge in Pt 4clusters. The graphene-based substrate is an ideal catalyst support, which makes the Pt catalyst loseelectron and weakens the CO adsorption. The results would be of great importance for designing high active nanoscale Pt catalysts used for fuel cells. © 2012 Springer Science+Business Media B.V.


Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Wang Q.,Henan Normal University | Wei S.,Henan Normal University
Surface Science | Year: 2011

The interaction of water molecules with the Zr-doped ceria (111) surface is investigated by using the DFT + U method. For the stoichiometric Zr-doped ceria (111) surface, a water molecule can be adsorbed not only through a one-H-bond configuration with its O* (oxygen of water) binding to a surface Ce ion, but also preferably through a nearly dissociated configuration with its O* binding to a surface Zr ion, at variance with that on the pure ceria (111) surface, where only a one-H-bond configuration is observed. While Zr-doping enhances the interaction of water with the unreduced CeO2(111), it reduces the tendency of water dissociation on the reduced ceria. On the first kind Ce0.75Zr0.25O2 - x(111) surface (V I, with a surface oxygen vacancy not neighboring a Zr dopant), water molecules prefer to dissociate around the Ce sites with the formation of the O*-Ce bond. On the second kind Ce0.75Zr0.25O 2 - x(111) surface (VII, with a surface oxygen vacancy neighboring a Zr dopant, which has a much higher formation probability than VI), the tendency of water dissociation (although preferred) is reduced compared with those on the CeO2 - x(111) and the first kind Ce0.75Zr0.25O2 - x(111). Additionally, the electronic interaction of water and the Zr-doped ceria (111) surface or the reduced Zr-doped ceria (111) surface is mainly from the interaction of the O*-Ce bond and the Hb-O bond because the charge affinity of Ce ions is stronger than that of Zr ions. Although the O* fills the vacancy site when a water molecule dissociates on the Ce0.75Zr 0.25O2 - x(111), it does not oxidize the surface. © 2010 Elsevier B.V. All rights reserved.


Tang Y.,Henan Normal University | Yang Z.,Henan Normal University | Yang Z.,Henan Key Laboratory of Photovoltaic Materials | Dai X.,Henan Normal University | Dai X.,Henan Key Laboratory of Photovoltaic Materials
Journal of Magnetism and Magnetic Materials | Year: 2011

The adsorption energies, stable configurations, electronic structures, and magnetic properties of the graphene with noble metal (NM=Pt, Ag, and Au) atom adsorption were investigated using first-principles density-functional theory. It is found that the bridge site is the most stable adsorption site for the Pt adatom; the Ag adatom can be stabilized almost equally at the bridge or the top site, while the Au adatom prefers to be adsorbed at top site. The Pt-graphene interaction is stronger than the interaction of Ag-graphene and Au-graphene, since the Pt atom has an unsaturated electronic d-shell (d9s 1). While there is no net magnetic moment for the Pt adatom, the Ag and Au adatoms still exhibit magnetic character on the graphene. The magnetic moments of the NMgraphene systems may be quenched (e.g., Ptgraphene), reduced (e.g., Aggraphene) or not changed (e.g., Augraphene) as compared with the values before adsorption. Therefore, the magnetic character of the adatomgraphene system can be turned by adsorbing different NM atoms on the graphene. © 2011 Elsevier B.V.

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