Recombination of hydrogen over Pt/TiO2 catalysts under ambient conditions
It has been reported that H2, which is very explosive gas in nuclear power plants. Therefore, in this study, we prepared a catalyst under different conditions its ability to oxide H2 at room temperature. And it was characterized by means of X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and CO-chemisorptions. The catalyst consisted of Pd or Pt/TiO2 and was prepared by the wet impregnation method. To assess the effects of pretreatment, the catalyst were prepared at 873K in a hydrogen atmosphere and at 673K in air atmosphere. When the conversion rate of H2 to H2O was compared for these catalysts, the catalyst prepared in hydrogen atmosphere displayed the perfect conversion rate at room temperature and pressure.
Control of titania nanodomain size as a route to modulate SMSI effect in Pt/TiO2 catalysts
Platinum based mesostructured SiO2 supported TiO2 nanoclusters (TiO2 content ranging from 10 to 50 wt.%) were synthesized and characterized. Titania nanodomains (< 4 nm) dispersed in the silica porosity are obtained. Derived 1 wt.% Pt/xTiO2-SiO2 nanocomposites were tested in the cyclohexane dehydrogenation reaction, a structure insensitive reaction to evaluate metal-support interaction. Pt/xTiO2-SiO2 nanocomposites display largely higher SMSI effect than measured over classical Pt/TiO2 P25 catalyst. While platinum particle size is found to be affected by the titania loading in the composite, similar SMSI effect is measured for all solids displaying similar TiO2 crystal size. Titania crystal size is evidenced as an important parameter allowing a control of the SMSI effect: the lower the crystal size, the stronger the metal-support interaction.
Cytoplsmic uridine phosphorylase of rat liver. Characterization and kinetics.
Abstract Uridine phosphorylase (uridine:orthophosphate ribosyltransferase, EC 2.4.2.3) of rat liver cytoplasm has been purified 1900-fold. Initial velocity patterns of the phosphorolysis of uridine or deoxyuridine and of the synthesis of uridine indicated a sequential mechanism. Product inhibition patterns with uracil or ribose 1-phosphate as inhibitors were consistent with an "ordered Bi Bi" reaction in which inorganic phosphate is the first substrate to bind to the enzyme and ribose 1-phosphate the last product to leave the enzyme. The most highly purified enzyme fractions still retained uridine-, deoxyuridine-, and thymidine-cleaving activities in the ratio of 10:7:1 at pH 7.4. The fractions separated into a major and a minor band of protein on electrophoresis in phosphate buffer. Aging of the enzyme with loss of activity resulted in an increase in the proportion of the minor band. The pH optimum of the enzyme for uridine cleavage was 8.2, for deoxyuridine cleavage, 6.5, and for uridine synthesis, 8.5. Uridine or deoxyuridine synthesis was inhibited 50% in the presence of 1 mm uracil. The enzyme did not catalyze the direct transfer of ribose from uridine to uracil in the absence of phosphate. Uridine protected the enzyme to a greater degree than phosphate against inhibition by o-iodosobenzoate. Thus, at least one sulfhydryl group and possibly three are present at or near the active site. Uridine cleavage, uridine synthesis, and deoxyuridine cleavage were inhibited by deoxyglucosylthymine. The phosphorolysis of deoxyuridine and thymidine by thymidine phosphorylase, also purified from rat liver cytoplasm, was not inhibited by deoxyglucosylthymine. The molecular weights of both uridine and thymidine phosphorylases were estimated to be 110,000.