Adsorption and reaction of CO on (Pd–)Al2O3 and (Pd–)ZrO2: vibrational spectroscopy of carbonate formation

γ-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 γ-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 cm−1 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

Plate-like zinc oxide microcrystals: Synthesis and characterization of a material active toward hydrogen adsorption

ZnO-based materials have been synthesized by means of hydrothermal method from aqueous solutions of ZnOH42- in the presence of sodium-dodecyl sulphate (SDS). By means of a variety of analyses (SEM, AFM, IR, UV-vis and XRD) it is shown that this synthesis method allows to obtain ZnO microcrystals with well defined morphology and active toward hydrogen adsorption. The adsorption of hydrogen on these zinc oxide platelets has been investigated by FTIR spectroscopy and the results are compared with those obtained on ZnO, synthesized by combustion of zinc metal. (C) 2006 Elsevier B.V. All rights reserved

Ferryl (Fe=O) termination of the hematite α-Fe₂O₃(0001) surface

Using scanning tunneling microscopy and infrared reflection absorption spectroscopy we have observed that the alpha-Fe2O3(0001) surface exhibits ferryl (Fe=O) groups, which may coexist with domains of the Fe-terminated surface. We therefore fully support ab initio calculations recently reported in the literature [W. Bergmeyer, H. Schweiger, and E. Wimmer, Phys. Rev. B 69, 195409 (2004)]. The close similarity to the results on the (0001) surfaces of Cr2O3 and V2O3 strongly suggests that the M=O termination under certain oxygen pressure conditions is the most stable for the close-packed surfaces of transition metal oxides with the corundum structure

Preparation and adsorption properties of activated porous carbons obtained using volatile zinc templating phases

High-surface-area activated micro/mesoporous carbons (SBET = 700\u20131900 m2/g) were obtained by a simple synthesis method, consisting in the ZnCl2-catalyzed polymerization of furfuryl alcohol followed by the polymer pyrolysis. The ZnCl2 salt, whose quantity exceeds that necessary for the polymerization reaction, acts both as template and as activating agent during the thermal treatment. Depending on the precursor quantities, carbons with prevailing micro- or meso-porous nature were obtained. The peculiar porosities make these materials suitable for testing the adsorption of molecules of different size (methylene blue and Cy-5 cyanine), which can constitute an easy method to qualitatively identify the micro/mesoporous nature of carbon materials