Supported Gold Nanoparticles as Catalysts in Peroxidative and Aerobic Oxidation of 1-Phenylethanol under Mild Conditions (original) (raw)
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Supported Gold Nanoparticles for Alcohols Oxidation in Continuous-Flow Heterogeneous Systems
ACS Sustainable Chemistry & Engineering
Gold nanoparticles (Au NPs) were anchored on alkynyl carbamate-functionalized support materials having the suitable features for application as catalysts in continuous-flow packed bed reactors. The functionalization step was carried out by grafting with the di-functional organosilane [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS) three commercial micrometer-sized oxide supports, i.e. silica, alumina, and titania. The alkynyl-carbamate moieties were capable to straightforwardly reduce the gold precursor HAuCl 4 yielding the supported Au NPs systems Au/SiO 2 @Yne, Au/Al 2 O 3 @Yne, and Au/TiO 2 @Yne. A comparison among the three materials revealed that silica allowed the highest organic functionalization (12 wt%) as well as the highest gold loading (3.7 wt%). Moreover, TEM investigation showed only for Au/SiO 2 @Yne the presence of homogeneously distributed, spherically shaped Au NPs (av. diameter 15 nm). Au/SiO 2 @Yne is an efficient catalyst, both in batch and flow conditions, in the oxidation of a large variety of alcohols, using H 2 O 2 as oxidizing agent, at a temperature of 90 °C. Furthermore, under flow conditions, the catalyst worked for over 50 h without any significant decrease in the catalytic activity. The catalytic activity of the three catalysts was evaluated and compared in the oxidation of 1-phenylethanol as a model substrate. We found that the flow approach plays a strategic role in preserving the physical and chemical integrity of the solid catalysts during its use, with remarkable consequences for the reaction conversion (from 2% in batch to 80 % in flow) in the case of Au/TiO 2 @Yne.
The vapor phase oxidation of benzyl alcohol was investigated over gold nanoparticles supported on mesoporous titanium dioxide (anatase) catalysts under aerobic conditions. The catalysts were prepared by homogeneous deposition–precipitation method using urea as the precipitating agent. The physico-chemical properties of the synthesized catalysts were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), pore size distribution (PSD), CO-chemisorption and X-ray photoelectron spectroscopy (XPS) techniques. The crystallite size of gold in Au/TiO2 catalysts was measured from XRD. The mesoporosity of TiO2 support and Au/TiO2 catalysts were confirmed by PSD analysis. TEM results suggest that gold nanoparticles are well dispersed over mesoporous TiO2. The catalytic functionality is well substantiated with particle size measured from TEM. XPS results reveal the formation of Au(0) after chemical reduction by NaBH4. The vapor phase benzyl alcohol oxidation was used as a test reaction to investigate the influence of the metal, nature of the support, and of metalsupport interactions in Au/TiO2 catalysts and also the catalytic activity and stability of the Au/TiO2 catalysts. The conversion of benzyl alcohol was found to increase with decrease in the size of gold particles. Smaller gold particles and a higher amount of small gold particles had a beneficial effect on the catalytic activity. The catalytic activity in the presence of oxygen is believed to be associated with the transport of electrons through the catalyst to the adsorbed oxygen on the surface.
The myth that gold cannot act as a catalyst has been discarded in view of recent studies, which have demonstrated the high catalytic efficiency of pure nano-gold and supported nano-gold catalysts. In recent years, numerous papers have described the use of supported nano-gold particles for catalysis in view of their action on CO and O 2 to form CO 2 , as well as a variety of other reactions. Special emphasis is placed on the oxidation studies undertaken on model nano-Au systems. In this work a solvent free oxidation of 1-phenyl ethanol was carried out using gold supported on ceria-silica, ceriatitania, ceria-zirconia and ceria-alumina at 160 0 C. Almost 88-97% conversion was obtained with >99% selectivity. Temperature screening was done from 70 to 160 0 C.Catalysts were prepared by deposition co-precipitation method and deposition was determined by EDEX analysis.
DOAJ (DOAJ: Directory of Open Access Journals), 2011
The myth that gold cannot act as a catalyst has been discarded in view of recent studies, which have demonstrated the high catalytic efficiency of pure nano-gold and supported nano-gold catalysts. In recent years, numerous papers have described the use of supported nano-gold particles for catalysis in view of their action on CO and O 2 to form CO 2 , as well as a variety of other reactions. Special emphasis is placed on the oxidation studies undertaken on model nano-Au systems. In this work a solvent free oxidation of 1-phenyl ethanol was carried out using gold supported on ceria-silica, ceriatitania, ceria-zirconia and ceria-alumina at 160 0 C. Almost 88-97% conversion was obtained with >99% selectivity. Temperature screening was done from 70 to 160 0 C.Catalysts were prepared by deposition co-precipitation method and deposition was determined by EDEX analysis.
2011
The myth that gold cannot act as a catalyst has been discarded in view of recent studies, which have demonstrated the high catalytic efficiency of pure nano-gold and supported nano-gold catalysts. In recent years, numerous papers have described the use of supported nano-gold particles for catalysis in view of their action on CO and O 2 to form CO 2 , as well as a variety of other reactions. Special emphasis is placed on the oxidation studies undertaken on model nano-Au systems. In this work a solvent free oxidation of 1-phenyl ethanol was carried out using gold supported on ceria-silica, ceriatitania, ceria-zirconia and ceria-alumina at 160 0 C. Almost 88-97% conversion was obtained with >99% selectivity. Temperature screening was done from 70 to 160 0 C.Catalysts were prepared by deposition co-precipitation method and deposition was determined by EDEX analysis.
2011
The myth that gold cannot act as a catalyst has been discarded in view of recent studies, which have demonstrated the high catalytic efficiency of pure nano-gold and supported nano-gold catalysts. In recent years, numerous papers have described the use of supported nano-gold particles for catalysis in view of their action on CO and O 2 to form CO 2 , as well as a variety of other reactions. Special emphasis is placed on the oxidation studies undertaken on model nano-Au systems. In this work a solvent free oxidation of 1-phenyl ethanol was carried out using gold supported on ceria-silica, ceriatitania, ceria-zirconia and ceria-alumina at 160 0 C. Almost 88-97% conversion was obtained with >99% selectivity. Temperature screening was done from 70 to 160 0 C.Catalysts were prepared by deposition co-precipitation method and deposition was determined by EDEX analysis.
Nanomaterials, 2020
This study aims to identify the role of the various electronic states of gold in the catalytic behavior of Au/MxOy/TiO2 (where MxOy are Fe2O3 or MgO) for the liquid phase oxidation of n-octanol, under mild conditions. For this purpose, Au/MxOy/TiO2 catalysts were prepared by deposition-precipitation with urea, varying the gold content (0.5 or 4 wt.%) and pretreatment conditions (H2 or O2), and characterized by low temperature nitrogen adsorption-desorption, X-ray powder diffraction (XRD), energy dispersive spectroscopy (EDX), scanning transmission electron microscopy-high angle annular dark field (STEM HAADF), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy of CO adsorption, temperature-programmable desorption (TPD) of ammonia and carbon dioxide, and X-ray photoelectron spectroscopy (XPS). Three states of gold were identified on the surface of the catalysts, Au0, Au1+ and Au3+, and their ratio determined the catalysts performance. Based on a comparison of catalyt...
Vapor Phase Oxidation of Benzyl Alcohol Over Gold Nanoparticles Supported on Mesoporous TiO2
Catalysis Letters, 2014
The vapor phase oxidation of benzyl alcohol was investigated over gold nanoparticles supported on mesoporous titanium dioxide (anatase) catalysts under aerobic conditions. The catalysts were prepared by homogeneous deposition-precipitation method using urea as the precipitating agent. The physico-chemical properties of the synthesized catalysts were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), pore size distribution (PSD), CO-chemisorption and X-ray photoelectron spectroscopy (XPS) techniques. The crystallite size of gold in Au/TiO 2 catalysts was measured from XRD. The mesoporosity of TiO 2 support and Au/TiO 2 catalysts were confirmed by PSD analysis. TEM results suggest that gold nanoparticles are well dispersed over mesoporous TiO 2. The catalytic functionality is well substantiated with particle size measured from TEM. XPS results reveal the formation of Au(0) after chemical reduction by NaBH 4. The vapor phase benzyl alcohol oxidation was used as a test reaction to investigate the influence of the metal, nature of the support, and of metalsupport interactions in Au/TiO 2 catalysts and also the catalytic activity and stability of the Au/TiO 2 catalysts. The conversion of benzyl alcohol was found to increase with decrease in the size of gold particles. Smaller gold particles and a higher amount of small gold particles had a beneficial effect on the catalytic activity. The catalytic activity in the presence of oxygen is believed to be associated with the transport of electrons through the catalyst to the adsorbed oxygen on the surface. Keywords Gold nanoparticles Á Mesoporous TiO 2 (anatase) Á Benzyl alcohol oxidation Á Benzaldehyde
Gold Nanoparticles Incarcerated in Nanoporous Syndiotactic Polystyrene Matrices as New and Efficient Catalysts for Alcohol Oxidations, 2012
The controlled synthesis of gold nanoparticles (AuNPs), incarcerated in a semicrystalline nanoporous polymer matrix that consisted of a syndiotactic polystyrene-co-cis-1,4-polybutadiene multi-block copolymer is described. This catalyst was successfully tested in the oxidation of primary and secondary alcohols, in which we used dioxygen as the oxidant under mild conditions. Accordingly, (±)-1-phenylethanol was oxidised to acetophenone in high yields (96 %) in 1 h, at 35 °C, whereas benzyl alcohol was quantitatively oxidised to benzaldehyde with a selectivity of 96 % in 6 h. The specific rate constants calculated from the corresponding kinetic plots were among the highest found for polymer-incarcerated AuNPs. Similar values in terms of reactivity and selectivity were found in the oxidation of primary alcohols, such as cinnamyl alcohol and 2-thiophenemethanol, and secondary alcohols, such as indanol and α-tetralol. The remarkable catalytic properties of this system were attributed to the formation, under these reaction conditions, of the nanoporous ε crystalline form of syndiotactic polystyrene, which ensures facile and selective accessibility for the substrates to the gold catalyst incarcerated in the polymer matrix. Moreover, the polymeric crystalline domains produced reversible physical cross-links that resulted in reduced gold leaching and also allowed the recovery and reuse of the catalyst. A comparison of catalytic performance between AuNPs and annealed AuNPs suggested that multiple twinned defective nanoparticles of about 9 nm in diameter constituted the active catalyst in these oxidation reactions.