Transition metal oxides spectroscopy

Wang L S 2000 Photodetachment photoelectron spectroscopy of transition metal oxide species Photoionization and Photodetaohment Advanced Series in Physical Chemistry 10, ed C Y Ng (Singapore World Scientific)... 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

A. A. Davydov, Infrared spectroscopy of adsorbed species on the surfaces of transition metal oxides, Wiley, Chichester, 1990. 

Methane-to-methanol conversion by gas-phase transition metal oxide cations has been extensively studied by experiment and theory see reviews by Schroder, Schwarz, and co-workers [18, 23, 134, 135] and by Metz [25, 136]. We have used photofragment spectroscopy to study the electronic spectroscopy of FeO" " [47, 137], NiO [25], and PtO [68], as well as the electronic and vibrational spectroscopy of intermediates of the FeO - - CH4 reaction. [45, 136] We have also used photoionization of FeO to characterize low lying, low spin electronic states of FeO [39]. Our results on the iron-containing molecules are presented in this section. 

Further resolution of the details of oxidative dehydrogenation requires the measurement of a catalyst s degree of reduction carried out during steady state reaction. We note that UV-visible spectroscopy offers a way to perform this measurement since many of the transition metal oxides which are active as oxidation catalysts exhibit striking color changes between their oxidized and reduced states. 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

Bruckner, A. and Kondratenko, E. (2006) Simultaneous operando EPR/UV-vis/laser-Raman spectroscopy - A powerful tool for monitoring transition metal oxide catalysts during reaction, Catal. Today, 113, 16. 

A.A. Davydov and C.H. Rochester, Infrared Spectroscopy of Adsorbed Species on the Surface of Transition Metal Oxides, Wiley, New York, 1990. 

Applications of In Situ Mossbauer Spectroscopy to the Study of Transition Metal Oxides... 

This work summarizes some applications of in situ Mossbauer spectroscopy to the study of certain aspects of the electrochemistry of iron and iron containing transition metal oxides. A number of illustrations of the use of this technique to the investigation of a wide variety of interfacial phenomena may be found in two recent monographs. (2 ... 

SCHERSON ET AL. Mossbauer Spectroscopy and Transition Metal Oxides 261... 

Figure 1.13 Raman spectra for a number of transition metal oxides supported on y-AI203 [75,102], Three distinct regions can be differentiated in these spectra, namely, the peaks around 1000 cm-1 assigned to the stretching frequency of terminal metal-oxygen double bonds, the features about 900 cm 1 corresponding to metal-oxygen stretches in tetrahedral coordination sites, and the low-frequency (<400 cm-1) range associated with oxygen-metal-oxygen deformation modes. Raman spectroscopy can clearly complement IR data for the characterization of solid catalysts. (Reproduced with permission from The American Chemical Society.)...

Electron paramagnetic resonance (EPR) spectroscopy. This is also known as electron spin resonance (ESR) spectroscopy and is the electron analogue of NMR. In the case of EPR, however, the magnetic moment is derived from unpaired electrons in free radical species and transition metal ions. The paramagnetism of many transition metal oxidation states has already been mentioned as a drawback to the observation of their NMR spectra, but it is the raison d etre behind EPR the technique is thus limited, in the case of metals, to those which are paramagnetic or which have free radicals as ligands. 

The excitation spectra coincides with the position of the charge-transfer spectra as measured by diffuse reflectance spectroscopy. In the case of supported transition-metal oxides, quenching of phosphorescence occurs on adsorption indicating that the luminescence centers are located at the surface, in contrast to mixed transition-metal oxides where these centers are in the bulk (160b). In many cases (71b,e, 160b,c,d), the quenching is reversible at room temperature and probably occurs via the formation of a weak complex. 

The first Raman spectra of bulk metal oxide catalysts were reported in 1971 by Leroy et al. (1971), who characterized the mixed metal oxide Fe2(MoC>4)3. In subsequent years, the Raman spectra of numerous pure and mixed bulk metal oxides were reported a summary in chronological order can be found in the 2002 review by Wachs (Wachs, 2002). Bulk metal oxide phases are readily observed by Raman spectroscopy, in both the unsupported and supported forms. Investigations of the effects of moisture on the molecular structures of supported transition metal oxides have provided insights into the structural dynamics of these catalysts. It is important to know the molecular states of a catalyst as they depend on the conditions, such as the reactive environment. 

Several major areas of interest can be recognized, namely (1) the state and location of metal cations and clusters in zeolites, (2) the nature of carbocations and unsaturated hydrocarbon species (exclusively in zeolites), and (3) the nature of oxide-supported highly dispersed transition metal oxide species. The first and the third of these areas show that UV-vis spectroscopy is a useful laboratory method for analyzing the local environment of metal cations in cases where long-range order is absent. 

The lithiated transition metal oxide LiVMoOe has been synthesized by solid state reaction. This is the first report of this compound to be studied as an anode material. The synthesized LiVMo06 powder has been studied by means of X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) spectroscopy. The electrochemical characteristics of the prepared electrodes assembled in coin cells were also investigated in terms of half-cell performance. It is observed that the cell exhibits three stages of discharge plateaus in the ranges 2.1-2.0 V, 0.6-0.5 V and 0.2-0.01 V, respectively. 

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