No abstract

No abstract

Recebido em 23/1/09; aceito em 4/12/09; publicado na web em 8/4/10 Titania-supported Ir catalysts were used in the hydrogenation of furfural. Reactions were carried out in a stirred batch type reactor at 0.62MPa and 363K using a 0.10M solution of furfural in a 1:1 mixture n-heptane -ethanol as solvent. Catalysts containing 2 wt% of Ir were reduced in H 2 flow at different temperatures in the range 473-773K. The catalysts were characterized by H 2 chemisorption, TEM, TPR, TPD of NH 3 and XPS. Conversion of furfural is higher at lower reduction temperatures, but leads to byproducts whereas reduction at higher temperatures shows selectivity to furfuryl alcohol close to 100%.

Cu2+ derived from aqueous CuC1, solutions and supported upon silica and anatase, but not alumina, shows asymmetric e.s.r. peaks and an absence of X.P.S. shake-up satellite peaks. Consideration is given to whether this may be attributed in part to its higher dispersion and different constrained symmetry. Divalent copper is stabilised by these oxide supports but in two different forms : one highly dispersed (with properties detectable by X.P.S. and e.s.r.) and the other poorly dispersed [as Cu,(OH),CI-type species on alumina and CuCl, on silica and anatase] characterisable by X.r.d. In respect to its effect upon the X.P.S. and reduction (but not e.s.r.) properties of supported Cu2+ species, rutile is different from anatase, a phenomenon which may be of some value in optimising activity of heterogeneous catalysts. The results cast doubt upon X.P.S. diagnosis of divalent copper. Resistivity measurements for titania-supported copper after reduction at 700 K suggest that very little of the copper may have been intercalated into the anatase support, but that on rutile such an intercalation may have been significant. This may be relevant to SMSI effects, especially at even higher reduction temperatures.

TiO 2 supported Ag nanoparticles with metal loading ranging from 2.0 to 12.0 wt.% have been prepared by reduction of a silver precursor with formic acid under mild conditions. XPS showed that silver remains in a reduced state and TEM has demonstrated that the procedure was effective to produce silver nanoparticles. Only small changes in the metal particle size from 2.0-3.4 nm occurs when the Ag content increases from 2.0 to 12.0 wt.%. O 2 TPD has revealed the presence of different types of adsorbed oxygen species being the one assigned to the active specie called O b which one displayed the highest proportion in the catalysts with higher metal loading. Catalytic activity in the conversion of methanol to formaldehyde showed that those samples with metal loading higher than 7.0 wt% displays higher yields compared to the unsupported silver catalyst.

No abstract

No abstract

The hydrogenation and dehydrogenation of cyclohexene has been studied in temperature-programmed and isothermal modes over oxide-supported Pt surfaces. The ratio of the rates of dehydrogenation: hydrogenation measured experimentally does not appear to correlate with that expected from standard thermodynamic free energies of formation. This modifi­cation of normal descriptions of catalysis could occur if reaction products separate and segregate on the Pt surface. Consideration is given to which sites may be predominantly responsible. Evidence of structure sensitivity is also highlighted.