55 research outputs found
Keggin heteropolyacid H3PW12O40 supported on different oxides for catalytic and catalytic photo-assisted propene hydration
Catalytic and catalytic photo-assisted hydration of propene to form 2-propanol in gasâsolid regime at
atmospheric pressure and 85 1C were carried out by using a heteropolyacid (POM) supported on different
oxides. Binary materials were prepared by impregnation of H3PW12O40 on different commercial and
home prepared supports (TiO2, SiO2, WO3, ZrO2, ZnO, Al2O3). Some of the composites were active both
for catalytic and catalytic photo-assisted reactions. The Keggin type POM was completely and partially
degraded, when supported on ZnO and Al2O3, respectively, and these binary solids always resulted as
inactive for both catalytic and catalytic photo-assisted reactions. The supported Keggin POM species
played a key role both for the catalytic and the photo-assisted catalytic reactions, due to their strong
acidity and ability to form strong oxidant species under UV irradiation, respectively. The contemporary
presence of heat and UV light improved the activity of almost all POM supported materials. All materials
were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM), diffuse
reflectance spectroscopy (DRS), determination of the conduction and valence band energy by photovoltage
measurements, Fourier transform infrared spectroscopy (FTIR), NH3-TPD experiments and time
resolved microwave conductivity (TRMC).
Introduction
Propene hydration to obtain 2-propanol is a reaction carried
out at moderate temperatures (ca. 150â200 1C) and pressure
(2MPa) in the presence of an acid catalyst;1 however the realization
of this reaction at ambient conditions is of great interest.
The us
Comprendre les comportements face Ă un risque modĂ©rĂ© dâinondation. Etude de cas dans le pĂ©riurbain toulousain (Sud-Ouest de la France)
Les espaces urbanisĂ©s soumis Ă des risques modĂ©rĂ©s dâinondation pour les vies humaines sont souvent peu considĂ©rĂ©s dans les Ă©tudes sur la vulnĂ©rabilitĂ© aux risques naturels en dĂ©pit des enjeux quâils reprĂ©sentent en termes de gestion de crise. Comment les riverains y font-ils face au danger et quelles sont leurs « bonnes raisons » dâagir? A partir de lâĂ©tude socio-gĂ©ographique de deux inondations rĂ©centes (2000 et 2003) dans la pĂ©riphĂ©rie toulousaine (Sud-Ouest de la France), nous montrons que les caractĂ©ristiques de lâalĂ©a dans les vallĂ©es Ă©tudiĂ©es influencent les reprĂ©sentations du risque et par consĂ©quent les motivations Ă se protĂ©ger. Face au risque majeur, la vulnĂ©rabilitĂ© sociale se trouve ainsi augmentĂ©e. Pour amĂ©liorer la rĂ©silience des populations, il convient dâadapter la communication sur les risques: personnaliser lâinformation, amĂ©liorer la comprĂ©hension de lâĂ©vĂ©nement vĂ©cu et mobiliser de nouvelles formes de mĂ©diation entre gestionnaires et riverains
Enhanced photocatalytic activity of octahedral anatase particles prepared by hydrothermal reaction
Octahedral anatase particles (OAPs) were prepared by hydrothermal reaction (HT) with various experimental conditions, including different amounts of titanate nanowires (TNWs), different water volumes and different pH values, to obtain products with high contents of OAPs. The properties of photocatalysts were investigated by XRD, SEM, TEM, XPS and time-resolved microwave conductivity (TRMC). Photocatalytic activities for oxidative decomposition of acetic acid (CO2 system) and anaerobic dehydrogenation of methanol (H-2 system) were tested. It was found that a larger amount and concentration of TNWs, as well as higher pressure during HT, resulted in the formation of smaller crystallites with higher density of mobile electrons. Enhanced photocatalytic activity, achieved for samples with the best morphology (higher content of OAPs), correlated with slower TRMC signal decay, i.e., slower recombination of charge carriers (e(-)/h(+)) probably due to lower content of deep electron traps. It was found that properties of platinum nanoparticles, deposited in-situ in the H-2 system in the absence or presence of pre-sparged oxygen, and their connection with OAPs were decisive factors for photocatalytic activity
Structural influence on charge carrier lifetimes in TiO2 powders studied by microwave absorption
Silver-modified octahedral anatase particles as plasmonic photocatalyst
Octahedral anatase particles (OAPs) were modified with silver nanoparticles (NPs) by photodeposition method. The properties of OAPs influenced the properties of silver deposits, and thus the photocatalytic activity of the obtained silver-modified OAPs. Photocatalytic activities were tested under UV and vis irradiation for oxidative decomposition of acetic acid and oxidation of 2-propanol, respectively. The properties of silver-modified OAPs were investigated by XRD, STEM, DRS, XPS and time-resolved microwave conductivity (TRMC) method. It was found that electron traps (ETs) worked as nucleation sites for silver, resulting in formation of smaller silver NPs on smaller OAPs with larger content of ETs. The modification with silver resulted in enhanced photocatalytic activity under both UV and vis irradiation. It was found that larger crystallite size of silver NPs, and thus larger polydispersity of silver deposits resulted in broad and intense plasmon resonance peak causing enhanced visible activity. The correlation between photocatalytic activity and TRMC data, e.g., slower decay of TRMC signal for more active samples, allowed discussion on property-governed photocatalytic activities of silver-modified titania
Electronic transport in semiconductor nanoparticles for photocatalytic and photovoltaic applications
It is shown by contactless transient photoconductance measurements that electron transport in TiO2 is highly dispersive and is strongly influienced by surface treatments. A fast recombination process is observed after band to band excitation. Oxalic acid absorbed at the surface slows the decay appreciably, as does alcoho
Photocatalytic and electronic properties of TiO2 powders elaborated by sol gel route and supercritical drying
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