Carbon Monoxide Oxidation Promoted by Surface Polarization Charges in a CuO/Ag Hybrid Catalyst.

Composite structures have been widely utilized to improve material performance. Here we report a semiconductor-metal hybrid structure (CuO/Ag) for CO oxidation that possesses very promising activity. Our first-principles calculations demonstrate that the significant improvement in this system's catalytic performance mainly comes from the polarized charge injection that results from the Schottky barrier formed at the CuO/Ag interface due to the work function differential there. Moreover, we propose a synergistic mechanism underlying the recovery process of this catalyst, which could significantly promote the recovery of oxygen vacancy created via the M-vK mechanism. These findings provide a new strategy for designing high performance heterogeneous catalysts

Solar Energy Conversion by Nanostructured TiO2

Research in solar energy conversion and the associated photoactive materials has attracted continuous interest. Due to its proper electronic band structure, high quantum efficiency, and photonic and chemical innerness, TiO2 has been demonstrated as a versatile oxide semiconductor capable of efficiently utilizing sunlight to produce electrical and chemical energy. Its outstanding physicochemical performances have led to an array of advanced photocatalytic and photoelectrochemical applications including environmental photocatalysis, dye/semiconductor-sensitized solar cell, and solar fuel productions

Carbon Monoxide Oxidation Promoted by Surface Polarization Charges in a CuO/Ag Hybrid Catalyst.

Composite structures have been widely utilized to improve material performance. Here we report a semiconductor-metal hybrid structure (CuO/Ag) for CO oxidation that possesses very promising activity. Our first-principles calculations demonstrate that the significant improvement in this system's catalytic performance mainly comes from the polarized charge injection that results from the Schottky barrier formed at the CuO/Ag interface due to the work function differential there. Moreover, we propose a synergistic mechanism underlying the recovery process of this catalyst, which could significantly promote the recovery of oxygen vacancy created via the M-vK mechanism. These findings provide a new strategy for designing high performance heterogeneous catalysts

A First-Principle Study of Synergized O₂ Activation and CO Oxidation by Ag Nanoparticles on TiO₂(101) Support

We performed density functional theory (DFT) calculations to investigate the synergized O₂ activation and CO oxidation by Ag₈ cluster on TiO₂(101) support. The excellent catalytic activity of the interfacial Ag atoms in O₂ dissociation is ascribed to the positive polarized charges, upshift of Ag d-band center, and assistance of surface Ti_5c atoms. CO oxidation then takes place via a two-step mechanism coupled with O₂ dissociation: (i) CO + O₂ → CO₂ + O and (ii) CO + O → CO₂. The synergistic effect of CO and O₂ activations reduces the oxidation energy barrier (<i>E</i>_a) of reaction (i), especially for the up-layered Ag atoms not in contact with support. It is found that the coadsorbed CO and O₂ on the up-layered Ag atoms form a metal-stable four-center O–O–CO structure motif substantially promoting CO oxidation. On the oxygen defective Ag₈/TiO₂(101) surface, because of the decreased positive charges and the down-shift of d-band centers in Ag, the metal cluster exhibits low O₂ adsorption and activation abilities. Although the dissociation of O₂ is facilitated by the TiO₂(101) defect sites, the dissociated O atoms would cover the defects so strongly that further CO oxidation would be prohibited unless much extra energy is introduced to recreate oxygen defects

Microscopic Insight into the Activation of O₂ by Au Nanoparticles on ZnO(101) Support

We carry out density functional theory calculations to cast insight on the microscopic mechanism of the activation of O₂ by Au₇ cluster on ZnO(101)-O support. The excellent catalytic activity of Au/ZnO catalyst was ascribed to the distribution of polarized surface charge associated with interface structure. It is found the stoichiometric ZnO(101)-O easily adsorbs and dissociates O₂ to form very stable oxygen-saturated surface. For Au₇ on stoichiometric ZnO(101)-O surface, the two Au atoms neighboring to O could accumulate positive charges, which then upshift the d-band centers toward the Fermi level. These favor the adsorption and dissociation of O₂, providing two Au activation sites. In contrast, for the Au₇ on the oxygen-saturated ZnO(101)-O, all Au atoms become neighboring to O and consequently provide seven activation sites. The workfunction difference between the Au₇ and support induces effective polarized surface charges, substantially promoting O₂ adsorption and dissociation both dynamically and thermodynamically. Further analysis on the effect of different Au positions demonstrates the polarized charge as the microscopic driving force for catalysis. These results would help design of better metal/oxide catalysts by providing important implications for the role of atomic and electronic structures

Theoretical Study of H₂O Adsorption on Zn₂GeO₄ Surfaces: Effects of Surface State and Structure–Activity Relationships

We employed the density functional theory to investigate the interaction of H₂O with Zn₂GeO₄ surfaces, considering both perfect and defective surfaces. The results revealed that the interaction of H₂O with Zn₂GeO₄ surfaces was dependent on the structure of the latter. For perfect surfaces, H₂O adsorbed at the Ge_3c···O_2c site of a (010) surface could spontaneously dissociate into an H atom and an OH group, whereas H₂O tended to adsorb at the O_2c-M_3c-O_3c site of a (001) surface by molecular adsorption. The presence of oxygen defects was found to strongly promote H₂O dissociation on the (010) surface. Analysis of the surface electronic structure showed a large density of Ge states at the top of the valence band for both perfect and defective (010) surfaces, which is an important factor affecting H₂O dissociation. In contrast, perfect and defective (001) surfaces with surface Ge states buried inside the valence band were significantly less reactive, and H₂O was adsorbed on these surfaces in the molecular form. This information about the adsorbate geometries, catalytic activity of various surface sites, specific electronic structure of surface Ge atoms, and their relevance to surface structure will be useful for the future design of the Zn₂GeO₄ photocatalyst, as well as for the atomistic-level understanding of other structure-sensitive reactions

Theoretical Study of H₂O Adsorption on Zn₂GeO₄ Surfaces: Effects of Surface State and Structure–Activity Relationships

We employed the density functional theory to investigate the interaction of H₂O with Zn₂GeO₄ surfaces, considering both perfect and defective surfaces. The results revealed that the interaction of H₂O with Zn₂GeO₄ surfaces was dependent on the structure of the latter. For perfect surfaces, H₂O adsorbed at the Ge_3c···O_2c site of a (010) surface could spontaneously dissociate into an H atom and an OH group, whereas H₂O tended to adsorb at the O_2c-M_3c-O_3c site of a (001) surface by molecular adsorption. The presence of oxygen defects was found to strongly promote H₂O dissociation on the (010) surface. Analysis of the surface electronic structure showed a large density of Ge states at the top of the valence band for both perfect and defective (010) surfaces, which is an important factor affecting H₂O dissociation. In contrast, perfect and defective (001) surfaces with surface Ge states buried inside the valence band were significantly less reactive, and H₂O was adsorbed on these surfaces in the molecular form. This information about the adsorbate geometries, catalytic activity of various surface sites, specific electronic structure of surface Ge atoms, and their relevance to surface structure will be useful for the future design of the Zn₂GeO₄ photocatalyst, as well as for the atomistic-level understanding of other structure-sensitive reactions

Theoretical Study of H₂O Adsorption on Zn₂GeO₄ Surfaces: Effects of Surface State and Structure–Activity Relationships

We employed the density functional theory to investigate the interaction of H₂O with Zn₂GeO₄ surfaces, considering both perfect and defective surfaces. The results revealed that the interaction of H₂O with Zn₂GeO₄ surfaces was dependent on the structure of the latter. For perfect surfaces, H₂O adsorbed at the Ge_3c···O_2c site of a (010) surface could spontaneously dissociate into an H atom and an OH group, whereas H₂O tended to adsorb at the O_2c-M_3c-O_3c site of a (001) surface by molecular adsorption. The presence of oxygen defects was found to strongly promote H₂O dissociation on the (010) surface. Analysis of the surface electronic structure showed a large density of Ge states at the top of the valence band for both perfect and defective (010) surfaces, which is an important factor affecting H₂O dissociation. In contrast, perfect and defective (001) surfaces with surface Ge states buried inside the valence band were significantly less reactive, and H₂O was adsorbed on these surfaces in the molecular form. This information about the adsorbate geometries, catalytic activity of various surface sites, specific electronic structure of surface Ge atoms, and their relevance to surface structure will be useful for the future design of the Zn₂GeO₄ photocatalyst, as well as for the atomistic-level understanding of other structure-sensitive reactions

Theoretical Study of H₂O Adsorption on Zn₂GeO₄ Surfaces: Effects of Surface State and Structure–Activity Relationships

We employed the density functional theory to investigate the interaction of H₂O with Zn₂GeO₄ surfaces, considering both perfect and defective surfaces. The results revealed that the interaction of H₂O with Zn₂GeO₄ surfaces was dependent on the structure of the latter. For perfect surfaces, H₂O adsorbed at the Ge_3c···O_2c site of a (010) surface could spontaneously dissociate into an H atom and an OH group, whereas H₂O tended to adsorb at the O_2c-M_3c-O_3c site of a (001) surface by molecular adsorption. The presence of oxygen defects was found to strongly promote H₂O dissociation on the (010) surface. Analysis of the surface electronic structure showed a large density of Ge states at the top of the valence band for both perfect and defective (010) surfaces, which is an important factor affecting H₂O dissociation. In contrast, perfect and defective (001) surfaces with surface Ge states buried inside the valence band were significantly less reactive, and H₂O was adsorbed on these surfaces in the molecular form. This information about the adsorbate geometries, catalytic activity of various surface sites, specific electronic structure of surface Ge atoms, and their relevance to surface structure will be useful for the future design of the Zn₂GeO₄ photocatalyst, as well as for the atomistic-level understanding of other structure-sensitive reactions