Metal deposition Raman spectroscopy

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

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). 

Metal dissolution is the inverse process to the deposition so its principles can be derived from preceding considerations. It should, however, be borne in mind that the preferred sites for deposition need not be the same as those for the dissolution. This is particularly true if the reactions are far from equilibrium. Therefore, rapid cycling of the potential between the deposition and the dissolution region can lead to a substantial roughening of the electrode surface, which can be used in techniques such as surface-enhanced Raman spectroscopy (see Chapter 15 ), which require a large surface area. 

Although several metal-containing heterocyclic compounds (such as porphyrins, phthalocyanines, naphthenates) are present in oil fractions most of the bench-scale research has been based on relatively rapid Ni, V, or Ni/V deposition procedures in which experimental FCC formulations have been artificially metal contaminated with solutions of Ni and/or V naphthenate dissolved in benzene (or toluene) (24). Metal levels in these novel FCC are usually above 0.5% that is well above the concentration that today exist on equilibrium FCC, see Figure 1. High metal concentration facilitate the study and characterization of Ni and V effects by modern characterization techniques such as X-ray photoelectron spectroscopy (XPS), Laser Raman spectroscopy (LRS), X-ray diffraction (XRD), electron microscopy, secondary ion mass spectrometry (SIMS), and 51V nuclear magnetic resonance (NMR). 

Extensive characterisation studies have been performed with various techniques (XAFS, XPS, 31P CP/MAS-NMR, IR and Raman spectroscopies)13 to characterise Aul after deposition, and its decomposition and conversion into metal particles upon thermal treatment. The transformation of hydroxide supports into oxides was also followed. The amorphous hydroxides contain a larger number of surface hydroxyl groups and surface defects than do the corresponding oxides, and they interact more efficiently with Aul, which dissociates on the surface, releasing the... 

The average oxidation state of a metal in a catalyst during reaction was found to be related to the presence of carbonaceous deposits on the surface. As the feed for propane ODH was depleted in O2, the catalyst was readily reduced (Mul et al., 2003) and amorphous carbon-containing deposits formed. This behavior was corroborated by UV-vis DRS (Mul et al., 2003 Puurunen and Weckhuysen, 2002) and by combination of UV-vis DRS and Raman spectroscopy (Kuba and Knozinger, 2002 Nijhuis et al., 2003). 

Reflection spectroscopy, Raman spectroscopy, and ellipsometry complement the various electrochemical methods to study metal deposition. The optical methods can be used for a direct monitoring of the deposition process. The great advantage of optical spectroscopy... 

Silver deposition is an example of a metal deposition, which can be monitored by Raman spectroscopy. A Raman spectrometer is now usually a Raman microscope using confocal... 

In this work different deposition teehniques were evaluated for the addition of metal nanoparticles to a contaminated area for in situ surface enhanced Raman spectroscopy. Also metallic colloids were added to solutions for Raman characterization at 7 meters of standoff distance. The goal was to combine SERS and a Raman telescope for remote detection of materials at trace levels. 

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