Not all that glitters... The activity of supported gold nanoparticles depends on the method used for their preparation. Gold clusters of about 2 nm in diameter were deposited on nonreducible metal oxides and carbon materials by solid grinding of a volatile organogold complex in a ball mill and subsequent calcination (see scheme). Au/ZrO2 and Au/Al2O3 prepared in this way were extremely efficient catalysts for the aerobic oxidation of glucose. (Chemical Equation Presented).
"Mechanochemistry, i.e. the induction of chemical reactions through the input of mechanical energy, has a long history in the context of materials processing such as ores and cements as well as in inorganic synthesis.      It has more recently been investigated for organic , metal–organic synthesis  and catalyst preparation.  The mechanochemical preparation of catalysts  is currently far less developed than the more traditional methods such as wet impregnation. "
[Show abstract][Hide abstract] ABSTRACT: Mechanochemical preparation of Ag/Al2O3 catalysts used for the selective catalytic reduction of NOx using hydrocarbons has been shown to substantially increase the activity of the catalyst in comparison with Ag/Al2O3 prepared by wet impregnation. The effect of using different ball-milling experimental parameters on both the structure of the material as well as the catalyst activity has been investigated and the optimum conditions established. A phase transition from γ- to α-alumina was observed milling at high speeds which was found to result in lower catalyst activities. At lower milling speeds both fracturing and agglomeration of the alumina support can be observed depending on the grinding time. However, due to ball-milling, a general enhancement in the NOx reduction activity was observed for all catalysts compared with the conventionally prepared catalysts irrespective of the reductant used. Transient DRIFTS-MS experiments were performed to investigate the effect of H2 in the absence and presence of water on the SCR reaction over catalysts prepared by both ball milling and wet impregnation. In-situ DRIFTS-MS analysis revealed significant differences in both gas phase and surface species. Most notably, isocyanate species were formed significantly more quickly and at higher surface concentration in the case of the mechanochemically prepared catalyst.
"In particular , gold nanoparticles deposited on metal oxide supports exhibit a high catalytic activity towards CO oxidation at low temperatures     . Different parameters, such as the size and shape of Au clusters, the nature of the support or the preparation method, play a crucial role in influencing the catalytic activity    . "
[Show abstract][Hide abstract] ABSTRACT: This study reports the interaction between metal oxides and gold in acidic media and its effect on the electrochemical oxidation of carbon monoxide. We describe the oxidation of CO in acidic media on Au nanoparticles of 3 and 7 nm on different oxide supports, diamond and carbon electrodes. In addition, the effect of a TiOx support on Au nanoparticles was mimicked by supporting TiOx nanoparticles on bulk gold. The comparison of these two systems strongly suggests that electronic interactions between Au and TiOx, rather than Au nanoparticle size effects, are the driving force of the catalytic activity in Au–TiOx.
Journal of Catalysis 03/2014; 311:182–189. DOI:10.1016/j.jcat.2013.11.020 · 6.92 Impact Factor
") for glucose oxidation that is comparable to the activity of the 2% Au/Al 2 O 3 catalyst with the similar gold dispersion prepared by deposition– precipitation and reported earlier . The apparent catalytic activity of the Au/C catalysts is lower than the activities of both the Au/Al 2 O 3 catalysts containing highly dispersed gold and Au/C catalysts prepared earlier by sol immobilization   or solid grinding  . Possible reasons for the lower TOF of the Au/C catalysts observed in this study are discussed below (Section 3.3). "
[Show abstract][Hide abstract] ABSTRACT: Aerobic oxidation of glucose in the presence of Au/Al2O3 catalysts with different dispersion of supported gold and Au/C catalysts containing highly dispersed gold nanoparticles was studied at varied glucose:Au molar ratios. The studies were focused on determining the contribution of the mass-transfer processes to the overall reaction kinetics in different regimes. The Au/Al2O3 catalysts were more active than the Au/C catalysts at high glucose:Au molar ratios. Among the alumina-supported catalysts with different metal dispersion, the highest TOF at high glucose:Au molar ratios was characteristic of the Au/Al2O3 catalysts bearing metal particles of 1–5 nm in size. Under these conditions, the high effectiveness factor of the Au/Al2O3 catalysts (>95%) was observed at a uniform gold distribution through the support granules. For the Au/C catalysts with the non-uniform distribution of gold nanoparticles through the catalyst grains, the apparent reaction rate was affected by internal diffusion (the effectiveness factor of a catalyst grain is ca. 70%), while the interface gas–liquid–solid oxygen transfer influenced the overall reaction kinetics as well. At a low glucose:Au molar ratio the reaction rate was limited by oxygen dissolution in the aqueous phase. In this mass transfer regime the rate of glucose oxidation over the carbon-supported catalysts exceeds the reaction rate over the alumina-supported catalyst, which is attributed to a higher adhesion of the hydrophobic carbon support to the gas–liquid interface facilitating the oxygen mass transfer towards catalytic sites.
Chemical Engineering Journal 05/2013; 223:921–931. DOI:10.1016/j.cej.2012.11.073 · 4.32 Impact Factor
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