Metal catalysts , Raman

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). 

Raman spectroscopy has been used for a long time in order to study supported and promoted metal catalysts and oxide catalysts [84] since many information can be obtained (1) identification of different metal oxide phases (2) structural transformations of metal oxide phases (3) location of the supported oxide on the oxide substrate and... 

Surface-enhanced Raman spectroscopy (SERS) has also been employed to characterize metal catalyst surfaces [103], The low sensitivity and severe conditions required for the signal enhancement have limited the use of this technique [104], but some interesting work has been published over the years in this area, including studies on model liquid-solid interfaces [105],... 

Laser Raman spectroscopy, 24 293-341 see also Raman spectroscopy molecular precursors for tailored metal catalysts, 38 298... 

Characterization Data for Oxide-Supported Metal Catalysts Employed by Research Groups Studying the Adsorption of Hydrocarbons by Infrared (IR) or Raman (Ra) Spectroscopy... 

Sheppard, N. and Nguyen, T.T. (1978) The vibrational spectra of carbon monoxide chemisorbed on the surfaces of metal catalysts - a suggested scheme of interpretation. Adv. Infrared Raman Spectrosc., 5, 67. 

The oxidation states of the elements in a catalyst can in some cases be determined by Raman spectroscopy. During some reactions on catalysts containing elements such as platinum, palladium, rhodium, copper, and silver, Raman experiments were used to detect the presence of oxide species. These cases are discussed in the section on Raman investigations of metal catalysts during operation. 

Bulk Mixed Oxide Catalysts. - Raman spectroscopy of bulk transition metal oxides encompasses a vast and well-established area of knowledge. Hie fundamental vibrational modes for many of the transitional metal oxide complexes have already been assigned and tabulated for systems in the solid and solution phases. Perhaps the most well-known and established of the metal oxides are the tungsten and molybdenum oxides because of their excellent Raman signals and applications in hydrotreating and oxidation catalysis. Examples of these two very important metal-oxide systems are presented below for bulk bismuth molybdate catalysts, in this section, and surface (two-dimensional) tungstate species in a later section. 

As a metal catalyst an Ni-Mn-Co alloy (70 25 5 wt%) was used. About 2% of the carbon yield was well crystallized diamond and the residue was most probably in an amorphous form, as was evident from X-ray powder dilfraction and Raman spectroscopic measurements. 

Sheppard, N., Nguyen, T.T. (1978). The Vibrational Spectra of Carbon Monoxide Chemisorbed on the Surface of Metal Catalysts - a Suggested Scheme of Interpretation, In Advances in Infrared and Raman Spectroscopy, R.J.H. Clark, R.E. Hester, (Ed.), pp. 67-147, Heyden Son Inc, ISBN 0-85501-185-8, Philadelphia, The United States of America... 

WA (1) not applicable for supported metal sulfides because they generally will become oxidized from combined exposure to laser heat and ambient oxygen (2) not applicable for metallic catalysts because they do not give rise to Raman signals. 

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