Cylindrical internal reflectance

Several nickel catalysts for the carbonylation of methanol have been reported,54"57 and an IR study has been described.58 The carbonylation of MeOH to form MeOAc and HOAc was studied using phosphine-modified Nil2 as the metal catalyst precursor. The reaction was monitored using a high-pressure, high-temperature, in situ Cylindrical Internal Reflectance FTIR reactor (CIR-REACTOR). 

The stability of phosphine-substituted Co clusters derived from Co4(CO)10(/r4-PPh)2 was examined under hydroformylation conditions using cylindrical internal reflectance (CIR) spectroscopy.148 [(CO)4Fe(//-PtBu2)Rh(CO)L], PPN[(CO)3CoO/-P(CMe3)2)Rh(CO)(HP(CMe3)2)], and... 

Moser, W. R., Reaction Monitoring by High-Pressure Cylindrical Internal-Reflectance and Optical-Fiber Coupled Reactors. In Moser, W. R., Slocum, D.W. (Eds.), Homogeneous Transition Metal-Catalyzed Reactions, American Chemical Society, Washington DC, 1992, Advanced Chemistry Series 230, p. 5. 

Final justification for using terms such as inner- or outer-sphere awaits direct spectroscopic confirmation. Electron Spin Resonance, Mossbauer, and Fourier Transform Infrared-Cylindrical Internal Reflection Spectroscopic techniques are being used to establish the structure of surface complexes (see, e.g., McBride, Ambe et al., and Zeltner et al., this volume). The potential for using EXAFS (extended x-ray absorption fine structure) to establish the type of surface complex for Pb + adsorbing onto goethite is currently being undertaken in our laboratory. 

Characterization of Anion Binding on Goethite Using Titration Calorimetry and Cylindrical Internal Reflection-Fourier Transform Infrared Spectroscopy... 

Titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy are two techniques which have seldom been applied to study reactions at the solid-liquid interface. In this paper, we describe these two techniques and their application to the investigation of salicylate ion adsorption in aqueous goethite (a-FeOOH) suspensions from pH 4 to 7. Evidence suggests that salicylate adsorbs on goethite by forming a chelate structure in which each salicylate ion replaces two hydroxyls attached to a single iron atom at the surface. 

To put things into perspective, we. can broadly classify these analytical methods into bulk, dry surface, and in situ interfacial techniques. This chapter focuses on the last category, illustrating two in situ techniques used to study anion binding at the goethite (a-FeOOH)-water interface titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. In fact, CIR-FTIR could prove to be extremely powerful, since it allows direct spectroscopic observation of ions adsorbed at the mineral-water interface. 

Cylindrical. Internal Reflection - Fourier Transform Infrared (CIR-FTIR) Spectroscopy... 

The ATR technique is now routinely used for IR spectroscopy as it allows measurement of spectra for a variety of sample types with minimal preparation. The crystals employed are generally prismatic in shape, allowing contact of a flat surface with the sample. The ATR method was first adapted for HP IR spectroscopy by Moser [29-33], who realised that a conventional autoclave could easily be adapted for in situ IR spectroscopy by fitting an ATR crystal of cylindrical cross section. The technique developed by Moser is thus known as cylindrical internal reflectance (CIR) spectroscopy and high pressure cells based upon the CIR method have been commercialised by Spectra-Tech. A typical CIR cell is illustrated in Figure 3.8. 

The rate for the Ir reaction was measured at temperatures up to 120 °C and CO pressures up to 6 bar in PhCl by IR using a cylindrical internal reflectance cell... 

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

Holmen, B.A. Tejedor-Tejedor, M.S. Casey, WA. (1997) Hydroxymate complexes in solution at the goethite/water interface. A. Cylindrical internal reflectance Fourier transform infrared spectroscopic study. Langmuir 13 2197... 

Tejedor-Tejedor, M.L Yost, E.C. Anderson, M.C. (1990a) Characterization of benzoic acid and phenolic complexes at the goethite/ aqueous solution interface using cylindrical internal reflectance Fourier transform infrared spectroscopy. Part 5 Methodology. Langmuir 6 979-987... 

Historically, high-pressure IR spectroscopy has been one of the most important methods to measure intermediates or resting-state species in catalytic cycles. In 1%8, Wilkinson observed HRh(PPh3)2(CO)2 in the Rh/PPh3 catalyst system by IR spectroscopy where an IR cell was connected via a tube to the autoclave. A related study was performed more recently by Moser et who applied their cylindrical internal reflectance IR cell. They determined the rate-... 

ATR studies of the biocorrosion of submerged copper surfaces have been reported. The IRE of a cylindrical internal reflectance cell (CIRCLE) was coated with a thin copper layer via a vacuum deposition technique (105). The copper layer reduces the sampling depth of the radiation outward from the surface of the IRE. Therefore, the intensity of the water bending band will vary with copper layer thicknesses of 4.1 nm or less. The copper layers were shown to be stable to exposure to water alone, but the presence of acidic polysaccahrides in the water caused a reduction in the copper layer thicknesses (106.107). The adsorption of a model compound, Gum Arabic, onto the coated IRE was detected by increases in the C-O stretching band of the pyranose units near 1050 cm"1 (106). 

Using a cylindrical internal reflectance (CIRcle) cell and GC-IR data collection software, it was determined for both lysozyme and BPN, that most of the enzyme adsorption occurred within ten seconds after injection. Nearly an order-of-magnitude more BPN adsorbed on the hydrophobic surface than the hydrophilic one, while lysozyme adsorbed somewhat more strongly to the hydrophilic Ge surface. Over time periods of about one day, the lysozyme layer continued to increase somewhat in thickness, while BPN maintained its initial coverage. 

Fig. 5.2.2. Liquid sampling according to the principle of cylindrical internal reflection (cylindrical attenuated total reflection = CATR). The CIRCLE (Spectra-Tech Inc.) device...

Sabo et al. [35] developed an LC/FTIR interface for both normal and reversed phase chromatography using an attenuated total reflectance cell. The cylindrical internal reflectance flow cell contained in a ZnSe crystal, had a nominal volume of 24 pi and an equivalent transmission cell path length of 4-22 pi over the usable range. On-the-fly spectra of the components from a 100 pi sample of a solution containing 2% of acetophenone and ethyl benzoate and 1% of nitrobenzene gave clearly identifiable spectra. Nevertheless, relative to other LC/FTIR systems this was not a very sensitive device. 

Holmen B. A., Tejedor-Tejedor M. I., and Casey W. H. (1997) Hydroxamate complexes in solution and at the goethite-water interface a cylindrical internal reflection Fourier transform infrared spectroscopy study. Langmuir 13, 2197-2206. 

Figure 10. Cylindrical internal reflectance (CIR) infrared spectra of humic and fiilvic acid size fractions A) 3K-1K molecular weight and B) 100-30K molecular weight isolated from water samples from Lake Bradford, Florida. The major bands are assigned as 1) C=0 asymmetrical stretch, 2) metal-bonded carboxyl asymmetrical stretch, 3) free carboxyl asymmetrical stretch, 4) carboxyl sym metrical stretch, and 5) C-C stretch.

Characterization of Aquatic Humic and Fulvic Materials by Cylindrical Internal Reflectance Infrared Spectroscopy... 

Cylindrical internal reflectance (CIR) techniques have been applied to humic and fulvic acids that were size fractionated by using hollow-fiber ultrafiltration methods with cutoffs of 0.1pm and 100,000, 30,000,... 

Cylindrical internal reflectance spectra were obtained on size-fractionated materials isolated from a small glaciated bog. Band assignments were made on the basis of their behavior under changing pH and comparison to model compounds. The bands appearing at about 1630 and 1390-1340 cm were assigned to the asymmetric and symmetric stretches of carboxylates bound to metal cations. The increased intensities for these bands in the smaller size fractions were found to be strongly correlated with increased cation content, consistent with this interpretation of the infrared spectra. 

Cylindrical internal reflectance infrared spectroscopy presents many advantages over conventional infrared techniques for the study of aquatic humic and fulvic materials. Samples can be studied in their natural state and in the aqueous environment from which they are isolated. Sample alterations due to drying and exposure to high pressures in the pellet forming process are avoided. In addition. 

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