35 research outputs found
Adsorption and reaction of CO on (Pdâ)Al2O3 and (Pdâ)ZrO2: vibrational spectroscopy of carbonate formation
Îł-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on Îł-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO2. The same was carried out for well-defined Pd nanoparticles supported on Al2O3 or ZrO2. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cmâ1 was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface
Metal Dispersion and Interaction with the Supports in the Coke Production Over Ethanol Steam Reforming Catalysts
reforming of ethanol. The catalytic performances, in terms of both H2 productivity
and stability towards coking and sintering, were related to the physico-chemical
properties of the catalysts.
The samples were prepared either by synthesis of the support by precipitation
and subsequent impregnation with the active phase, or by direct synthesis through
Flame Pyrolysis. Many techniques have been used to assess the physico-chemical
properties of both the fresh and spent catalysts. The samples showed different
textural, structural and morphological properties, as well as different reducibility
and thermal resistance, depending on the preparation method and support.
The performance of the titania-supported catalysts were found very dependent
on the preparation procedure, and we may conclude that operation at 625 C can be
satisfactory from all the points of view of activity, productivity and C balance,
allowing to limit the heat input to the reactor with respect to operation at 750 C