The rate of hydrogen evolution, r(H 2), due to the photocatalysed reforming of methanol, MeOH, is studied as a function of Pt loading on P25 TiO 2 both in the aqueous (at room temperature) and gas phase (at 100 o C). A similar study, using Pd on P25, has been reported earlier [M. Bowker et al. J. Catalysis, 2003, 217, 427-433] and a perimeter-based Metal-Support Interface (MSI) kinetic model used to interpret the results. Here a new kinetic model is introduced which appears to provide a better fit to all the r(H 2) vs wt% metal data sets, in which the rate of reaction is proportional to an extended area around each metal island, rather than its perimeter. A simple theoretical rationale is provided for this expanding photocatalytic area and overlap (EPAO) kinetic model in which each metal island forms an electric field with the surrounding TiO 2 so as to act as a sink for electrons photogenerated in the surrounding TiO 2 film, thereby allowing it to effect the reduction of water, leaving the remaining photogenerated holes to oxidise the methanol adsorbed on the TiO 2. Some support for this very simple kinetic and theoretical model is provided by the results of a brief study of the oxidation of soot deposited on and around a Pt 'dot' on a sol-gel TiO 2 film, in that, upon irradiation of this system a zone of activity is visibly revealed by the gradual disappearance of the soot around the Pt 'dot', the radius of which appears to be proportional to the radius of the metal 'dot'.
A number of different M/TiO 2 photocatalysts, where M (the co-catalyst) = Pt, Pd, Au and Ag, are used to drive the steam reforming of methanol (MeOH) in a gas phase continuous flow reactor operated at 100 o C. The rate of H 2 production is: Pt > Pd > Au > Ag >> no metal. The photonic efficiency of Pt/TiO 2 photocatalyst is ca. 120% which suggests some of the hydrogen derives from a current-doubling reaction mechanism. The Pt/TiO 2 photocatalyst drives the steam reforming of MeOH, which generates H 2 and CO 2 , with an apparent selectivity of 100% over a wide UV irradiance range (i.e. 1-9.5 mW cm-2 at 365 nm). In contrast, in the dark, the decomposition of MeOH, which generates H 2 and CO, dominates with a selectivity of ca. 79%. In contrast to Pt, the Pd/TiO 2 photocatalyst is non-selective to either MeOH reforming or its decomposition, so that CO 2 and CO are generated with equal rates. The Au and Ag photocatalysts are less active than either the Pt or Pd co-catalysts and exhibit a variation in selectivity with UV irradiance which is intermediate between that of Pt and Pd. The possible use of photocatalysis as a means to generate H 2 from alcohol-based biofuels is briefly discussed.
Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD), the third enzyme of the mitochondrial beta-oxidation pathway, carries out the dehydrogenation of 3-hydroxyacyl-CoA compounds of 12-18 carbon length. To date only nine cases of LCHAD deficiency have been documented. We report a further patient who as a neonate developed non-specific gastrointestinal symptoms and at 5 months of age cardiomyopathy, recurrent hypoketotic hypoglycaemia and gross alterations of plasma carnitine fractions. Dietary management with medium chain triglycerides led rapidly to clinical improvement. There was a close correlation between the clinical condition, plasma carnitine fractions and cardiac function. At 2 years of age she is developing normally.
Clearly discernible rings of high photocatalytic activity, i.e. rings of activation, RoAs, are formed around Pt macro-sized (radius: ro 1 mm radius) Pt islands, i.e. Pt 'dots', deposited on TiO2 films, which have been covered with a visible pollutant, such as soot, or a dye, such as acid orange 7, AO7. The features of the RoA region appear very similar for soot or dye-covered films. Thus, the radius of the RoA region, ra, appears to depend weakly, if at all, on ro, and is typically 0.60-0.68 mm > ro. The rate of photocatalytic removal of the surface pollutant inside the RoA is uniform and significantly greater, i.e. ca. 3.2 -5 x's, than that outside the RoA region. RoA region formation is observed for: (i) Pt dots which have been photodeposited or created through thermal reduction, (ii) Pt dots on sol-gel and commercial (paints and tiles) TiO2 films and (iii) Pd dots, but less clearly for Au dots. A simple mechanistic rationale for RoA region formation is presented and the potential importance of this feature, with regard to improving the performance of commercial photocatalytic films, is discussed briefly.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.