ABSTRACT
We report here the Raman spectrum and lattice dynamics study of a well-crystallized ß-V(2)O(5) material prepared via a high-temperature/high-pressure (HT/HP) route, using α-V(2)O(5) as the precursor. Periodic quantum-chemical density functional theory calculations show good agreement with the experimental results and allow one to assign the observed spectral features to specific vibrational modes in the ß-V(2)O(5) polymorph. Key structure-spectrum relationships are extracted from comparative analysis of the vibrational states of the ß-V(2)O(5) and α-V(2)O(5) structures, and spectral patterns specific to the basic units of the two V(2)O(5) phases are proposed for the first time. Such results open the way for the use of Raman spectroscopy for the structural characterization of vanadium oxide-based host lattices of interest in the field of lithium batteries and help us to greatly understand the atomistic mechanism involved in the α-to-ß phase transition of vanadium pentoxide.
ABSTRACT
A catalyst composed of a Pd(5)Cu mixed oxide supported over Al(2)O(3)-CeO(2) with general formula Pd(5)CuO(x)/Al(2)O(3)-CeO(2) (Al/Ce atomic ratio=1/1) has been prepared by a wet impregnation method and tested in the methanol conversion. The structural and morphological characterization of the catalyst evidences that it is a mesoporous material thermally stable up to 873 K. At that temperature the specific surface area value is 170 m(2)/g, and a CeO(2) cubic phase is identified together with ill-defined diffraction peaks tentatively assigned to Cu-Pd clusters, suggesting that the active phase is well dispersed over the support. Infrared studies prove that methanol conversion takes place over the catalyst to a high extent yielding syngas as main product in the range 473-723 K and methane at higher temperatures. Oxygenated intermediates containing methoxy, carbonile or formiate species are not detected, which evidences that methanol conversion to methane very probably takes place according to a via-carbide mechanism.
