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.

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.

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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 NM(4) 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 CeO(2)(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 CeO(2)(111) surface. The reaction of [Formula: see text] 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 CeO(2)(111) surface. The three base atoms of the small clusters that bonded with the CeO(2)(111) surface showed positive charges, while the top metal atoms of the NM(4) clusters had a small negative charge.

The binding of a single metal atom (Pt, Pd, Au, and Sn) nearby a single-vacancy (SV) on the graphene is investigated using the first-principles density-functional theory. On the pristine graphene (pri-graphene), the Pt, Pd, and Sn prefer to be adsorbed at the bridge site, while Au prefers the top site. On the graphene with a single-vacancy (SV-graphene), all the metal atoms prefer to be trapped at the vacancy site and appear as dopants. However, the trapping abilities of the SV-graphene are varied for different metal atoms, i.e., the Pt and Pd have the larger trapping zones than do the others. The diffusion barrier of a metal atom on the SV-graphene is much higher than that on the pri-graphene, and the Pt atom has the largest diffusion barrier from the SV site to the neighboring bridge sites. On the SV-graphene, more electrons are transferred from the adatoms (or dopants) to the carbon atoms at the defect site, which induces changes in the electronic structures and magnetic properties of the systems. This work provides valuable information on the selectivity of lattice vacancy in trapping metal atoms, which would be vital for the atomic-scale design of new metal-carbon nanostructures and graphene-based catalysts.