Atomic-Scale Explanation of O₂Activation at the Au–TiO₂Interface

Abstract

By a combination of electron paramagnetic resonance spectroscopy, finite-temperature ab initio simulations, and electronic structure analyses, the activation of molecular dioxygen at the interface of gold nanoparticles and titania in Au/TiO2 catalysts is explained at the atomic scale by tracing processes down to the molecular orbital picture. Direct evidence is provided that excess electrons in TiO2, for example created by photoexcitation of the semiconductor, migrate to the gold particles and from there to oxygen molecules adsorbed at gold/titania perimeter sites. Superoxide species are formed more efficiently in this way than on the bare TiO2 surface. This catalytic effect of the gold nanoparticles is attributed to a weakening of the internal O–O bond, leading to a preferential splitting of the molecule at shorter bond lengths together with a 70% decrease of the dissociation free energy barrier compared to the non-catalyzed case on bare TiO2. The findings are an important step forward in the clarification of the role of gold in (photo)­catalytic processes.

Photo–thermo Catalytic Oxidation over a TiO2‐WO3‐Supported Platinum Catalyst

“…In the dark, the symmetric signal at g = 2.003 is ac onsequence of unpaired electrons trapped at the oxygen vacancies in TiO 2 , [23] and the prominent signal at g = 1.979 is attributed to Ti 3+ in the rutile lattice of Degussa P25. [24] Upon continuous illumination for 5minutes,as et of paramagnetic superoxide anion O 2 À (g xx = 2.002, g yy = 2.010, g zz = 2.026) signals were observed on the reduced Pt/TiO 2 -WO 3 catalyst. [25] Meanwhile,t he EPR signals of O 2 À weaken considerably under light once C 3 H 8 is introduced, signifying that O 2 À can react with C 3 H 8 even at 100 K ( Figure 5b).…”

Mesoporous Co‐Al oxide nanosheets as highly efficient catalysts for CO oxidation

“…In combination with the XRD (Figure ) characterization of the surface composition and structure of the catalyst, it can be concluded that the Co x Al‐Ns are likely similar to those of the Co 3 O 4 material, and the difference in their catalytic activities may originate from different numbers of the active sites. Because the activation of O 2 is a key step in the CO oxidation reaction, and the adsorption of O 2 results in the formation of active oxygen species, the number of catalytically active sites is expected to show a positive correlation with the O 2 adsorption capacity of the catalysts. Therefore, we compared the O 2 adsorption capacity of the catalysts, as measured by O 2 ‐TPD experiments (Figure a).…”

“…K E Y W O R D S CO oxidation, Co-Al oxide, mesoporous nanosheet, stable catalyst 1 | INTRODUCTIONThe oxidation of carbon monoxide (CO) over heterogeneous catalysts is of great importance due not only to the practical applications in automotive gas treatment, indoor air cleaning, and CO removal from H 2 feed gas for fuel cells, but also to its use as a model reaction in laboratory research. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Up to now, many highly efficient catalysts for CO oxidation, mainly including supported noble metals (such as Au and Pt) 8,9,11,12,[19][20][21][22][23][24][25] and metal-oxides (such as Co 3 O 4 and MnO 2 ) have been successfully developed. 7,[13][14][15][16][17][18][26][27][28][29][30][31][32][33] For example, TiO 2 -supported Au catalyst is very active for CO oxidation at the temperature of −70 C. 1...…”

Cl2 Production by Photocatalytic Oxidation of HCl over TiO2

“…The mechanism of ORR likely starts by forming superoxide radicals through electron uptake by adsorbed O 2 . [21,22] Protonation by HCl yields hydroperoxyl radicals, whose reduction can form hydrogen peroxide, which decomposes into hydroxyl radicals under illumination. Such species generally show rapid interconversion.…”