Classical strong metal-support interactions between gold nanoparticles and titanium dioxide (original) (raw)
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Journal of Catalysis, 1999
Catalytically active gold model catalysts have been designed via "size-controlled" gold colloids of 2-nm mean particle size. They were prepared by reduction of chloroauric acid with tetrakis-(hydroxymethyl)phosphonium chloride in an alkaline solution, followed by adsorption of gold colloids on TiO 2 and ZrO 2 at a pH lower than the isoelectric point of the metal oxides. Investigation of the size of the gold particles in solution by UV-vis spectrophotometry in combination with HRTEM indicated that the gold colloids are rather stable in alkaline solution, during pH-change and purification with dialysis. Ageing of the solutions showed that the particle size slowly increased over a time scale of 4 months. Analysis of the dried catalysts by XRD and HRTEM corroborated that the particle size was nearly preserved during the immobilization process. Only in the case of high loadings (16.6 wt%, compared to the calculated nominal monolayer coverage of 45-55 wt%), incomplete adsorption occurred, affording more inhomogeneous dispersion and some aggregation. After calcination at 673 K, both zirconia-and titaniabased catalysts containing 1.7 wt% Au exhibited high activity in low temperature CO oxidation. Although the particle size on both supports was comparable, the Au/TiO 2 catalyst showed significantly higher activity than the Au/ZrO 2 catalyst. The uncalcined Au/TiO 2 also exhibited high activity, whereas the uncalcined Au/ZrO 2 was inactive under the same conditions, corroborating that not only the gold particle size but also the support plays a key role in CO oxidation.
Insights into the reactivity of supported Au nanoparticles: combining theory and experiments
Topics in Catalysis, 2007
The origin of the extraordinary catalytic activity of gold nanoparticles is discussed on the basis of density-functional calculations, adsorption studies on single crystal surfaces, and activity measurements on well characterized supported gold particles. A number of factors are identified contributing to the activity, and it is suggested that it is useful to consider lowcoordinated Au atoms as the active sites, for example, CO oxidation and that the effect of the support can be viewed as structural and electronic promotion. We identify the adsorption energy of oxygen and the Au-support interface energy as important parameters determining the catalytic activity.
Gold catalysts: A new insight into the molecular adsorption and CO oxidation
Chemical Engineering Journal, 2009
The molecular adsorption and CO oxidation on a gold-deposited TiO 2 catalyst were investigated by means of molecular dynamics simulation. The results indicate that the molecules (i.e., O 2 , CO, and H 2 O) are selectively adsorbed on the specific locations such as gold particle, gold-support perimeter interface, and support surface. The adsorption and dissociation of H 2 O molecules at the perimeter interface enhance the supply of oxygen, thus promoting the oxidation of CO on the Au/TiO 2 catalyst. However, the presence of Cl − ions could significantly impede CO oxidation due to their competition with O 2 , CO, and H 2 O for the adsorption sites. A reaction mechanism of CO oxidation is postulated on this basis. The findings are useful in developing a comprehensive picture about CO oxidation on gold-deposited TiO 2 and in the design of new gold catalysts with high catalytic activity.
Applied Catalysis A: General, 2006
Nanostructured gold catalysts supported on CeO 2 and SiO 2 were prepared by the deposition-precipitation (DP) and the solvated metal atom dispersion (SMAD) techniques. The structural and electronic properties of the catalysts were investigated by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Gold was found as small metal nanoparticles (cluster size $2 nm) in the SMAD-prepared samples and in ionic state in the DP catalysts. The catalytic activity of the samples was tested in the reaction of low temperature CO oxidation. Gold nanosized particles in a pure metallic state exhibited a worse catalytic performance, both on ceria and silica. The presence of non-metallic Au species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The higher activity of the Au/CeO 2 (DP) sample with respect to the Au/SiO 2 (DP) catalyst can be ascribed to a better stabilization of the Au +1 ions, probably as AuOspecies, by the cerium oxide. #
Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts
Chemical Reviews, 2020
In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO 2 hydrogenation, C−C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts. CONTENTS 1. Introduction 3890 2. The Role of the Support during Catalyst Synthesis 3891 2.1. Preparing Au Catalysts on Oxides and Other Conventional Supports 3891 2.2. Preparing Au Catalysts on "Engineered"
Gold Nanoparticle: Enhanced CO Oxidation at Low Temperatures by Using Fe-Doped TiO2 as Support
Catalysis Letters, 2017
Iron doped TiO 2 materials were prepared by the sol-gel method and used as supports of gold nanoparticles synthesized by the deposition-precipitation technique. The gold-iron-titania catalysts were characterized by X-ray diffraction, Raman spectroscopy, N 2 physisorption, UV-Vis spectroscopy as a function of temperature, H 2-temperature programmed reduction, transmission electronic microscopy and X-ray photoelectron spectroscopy. The gold-iron catalysts were catalytically active during the CO oxidation reaction at low temperatures, reaching CO conversion percentages of almost 80% at room temperature. The Au/TiO 2-Fe catalyst surface was characterized through infrared spectroscopy (DRIFTS) during the CO oxidation reaction to elucidate the active sites and the real carbon monoxide interaction during the reaction. A 24-h deactivation test corroborated a final deactivation of the catalysts of only 25% for both Au/TiO 2-Fe 1 and the bare Au/TiO 2. The results here obtained corroborate that the activity of the iron-doped TiO 2 catalyst was higher than that of the bare TiO 2 due to the iron incorporation into the TiO 2 lattice, which allows the formation of surface oxygen vacancies and new adsorption sites which favor the CO adsorption and its oxidation to CO 2 .
Au/TiO2 nanostructured catalyst: effects of gold particle sizes on CO oxidation at 90 K
Materials Science and Engineering: C, 2001
An FTIR study of CO adsorption and oxidation at 90 K on gold-titania catalysts is presented, concerning three nanostructured AurTiO catalysts, with the same gold loading, calcined at three different temperatures and with different gold particle mean sizes of 2.4, 2 2.5 and 10.6 nm. On all the samples, the CO adsorption and different CO-18 O interactions were examined. From the experimental 2 Ž . results, it can be deduced that: i at 90 K, carbon monoxide and oxygen are molecularly and competitively adsorbed on gold step sites; Ž .