The effect of coating TiO 2 on the CO oxidation of the Pt/c-alumina catalysts was observed through activity tests and surface characterization spectroscopy by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) experiments. XPS results evidenced the occurrence of different Pt 2? species and metallic Pt 0 at the surface which suggest electron transfer of titanium (cation) to the platinum atom and the reduction of titanium (Ti 4? ? Ti 3? ). FTIR analyses suggested oxygen spillover mechanism at the interface between titanium dioxide and platinum that may explain the catalytic activity of the platinum titania-supported catalysts. The apparent activation energy for the CO oxidation was 52.5 kJ/mol and similar for all catalysts. However, the frequency factor changed significantly, indicating interfacial phenomena caused by CO and oxygen adsorptions over TiO x species and Al 2 O 3 support with similar dispersions.
Using in situ X-ray
diffraction and the Rietveld method combined
with the maximum entropy method, we investigated the interaction of
water with sodium faujasite and determined the sodium and water sorption
sites as a function of water content. From the information contained
in the lowest diffraction-angle peaks, we found that water also interacts
with faujasite, forming a shell-like layer inside the supercages located
at a mean distance of 2.8 Å from the pore-wall oxygens. For water-saturated
faujasite, this shell has a surface density comparable to liquid water.
The ion-exchange sites and ordered water found inside the supercage
are embedded in this layer. We included the water shell contribution
in Rietveld refinements by modeling it as a hollow sphere scatterer
inside the faujasite supercages, and the refined water and cation
quantities have agreed with nominal values.
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