In situ UV-Vis

Equilibria between Peroxo and Hydroperoxo species in the TS-I/H2O2/H2O System In Situ UV-Vis DRS... 

Summarizing, the in situ UV-Vis, XANES, and EXAFS studies of Bonino et al. [49] and of Prestipino et al. [50] on hydrated and anhydrous peroxo/hy-droperoxo complexes on crystalhne microporous and amorphous meso-porous titanosilicates have shown, for the first time, the equilibriiun between r] side-on and end-on complexes. The amount of water is the key factor in the equilibrium displacement. In this regard please note that, owing to the hydrophobic character of TS-1, substrates such as olefins are the dominant species in the channels. This fact assures a relatively local low concentration of water, which in turn guarantees a sufficient presence of the active end-on... 

In 1993, we examined formation processes of PVP-protected AuPt bimetallic nanoparticles by in-situ UV-Vis spectroscopy during the reduction [53]. Figure 8 shows the in-situ UV-Vis spectra during the simultaneous reduction of Au(III) and Pt(IV) ions. In the case of PVP-protected AuPt bimetallic system, Au(III) ions are... 

Figure 8. In-situ UV-Vis spectra during the formation of PVP-protected AuPt (1 1) bimetallic system in the region of l<350nm (a) and 1>350 nm (b). (a) Sampling from the solution of the metal ions in ordinary conditions for preparation at 100 °C with refluxing (b) the solution of the metal ions in a quartz UV cell was heated up to 80 °C without refluxing. (Reprinted from Ref [53], 1993, with permission from Elsevier.)...

Figure 29. In situ UV/Vis spectra for propylene epoxidation on Au/Ti-Si02 [88] (bottom BaS04 referenced, and top Ti-Si02 referenced) (a) under Ar at 298 K before propylene epoxidation, (b) under C3Hs/H2/02/Ar at 423 K for 120 min, (c) under C3H JH2/O2/ Ar at 423 K for 270 min, (d) under Ar at 298 K after propylene epoxidation. Offsets are used for clarity.

In situ UV-Vis Diffuse Reflectance Spectroscopy was performed under reactive atmosphere ( -butane/oxygen). These experiments confirmed that submitting the catalyst to the reaction mixture favors the development of a more oxidized active surface, and that the extent of transformation depends on the reaction temperature and on the catalyst P/V ratio. For instance, catalyst P/V 1.06 was less oxidized than catalyst P/V 1.00 at a temperature lower than 340°C. X-ray Photoelectron spectra of catalysts recorded after reaction at 380°C confirmed that catalyst P/V 1.00 was considerably more oxidized (average oxidation state for surface V 4.23) than the P/V 1.06 catalyst (average oxidation state 4.03). 

Wichterlova, B., Sazama, P., Breen, J.P. et al. (2005) An in situ UV-vis and FTIR spectroscopy study of the effect of H2 and CO during the selective catalytic reduction of nitrogen oxides over a silver alumina catalyst, J. Catal. 235, 195. 

If no references for the degradation products or impurities are available in the laboratory, the sample should be exposed to stress conditions such as heat (50-80 °C), ultraviolet light (2000 lux), acid and base (0.1-1 M HC1 and NaOH), and oxidant (3% H2O2). After incubation in the allotted time, the purity and identity of the analyte peak/spot should be proved by using DAD or MS detection (for LC), MS (for GC), or in situ UV-Vis measurement using a densitometry or TLC-MALDI MS (for TLC). 

Ni(sacsac)P(nBu3)Cl (sacsac = pentane-2,4-dithionate) was activated by AlEt2Cl to form a catalytically active species for the oligomerization of ethene and propene. This study is noteworthy in that it uses in situ UV-VIS spectroscopy to monitor the course of the polymerization. In this reaction, the aluminum reagent serves both to activate the transition metal and to scavenge any moisture present. 

During in situ UV-vis spectroelectrochemical work, it is easier to obtain spectra by using a single-beam instrument. At the start of the experiment, the analyst sets the absorbance to zero with the in situ cell placed in the path of the beam, so the cell then acts as a spectroscopic blank or ( reference ). Any changes in absorption will relate to the changes in the amounts of each of the redox states within the cell, rather than from the cell itself. 

The most common errors encountered in situ UV-vis spectroelectrochemistry result from total internal reflection (TIR) (causing ringing ) and carrying out analyses at wavelengths beyond the band edge. 

J. van den Broeke, G. Langergraber, A. Weingartner, On-line and in-situ UV/vis spectroscopy for multi parameter measurements a brief review. Spectroscopy Europe, 18(4), 15-18 (2006). 

Coreduction of Au and Pt ions by refluxing alcohol in the presence of PVP gives the colloidal dispersions of Au-core/Pt-shell structured bimetallic nanoparticles, as mentioned before. The formation of this bimetallic nanoparticles was traced by in situ UV-Vis spectra (68). The spectral change is shown in Figure 9.1.15, in which the peaks ascertained to be the metal ions disappear at first, and then the broad tailing peaks due to the colloidal dispersions appear. More precisely speaking, the tetrachloroauric(III) acid (at —320 nm) is reduced first, followed by reduction of hexachloroplatinic(IV) acid (at —265 nm). This order of reduction is consistent with the standard redox potential of the two metal ions. After the reduction of two... 

UV-Vis spectroscopy — Electronic absorption in the UV-Vis range by species generated during electrochemical reactions or being present at the electrochemical interface between the electronically conducting electrode and an ionically conducting phase (electrolyte solution, molten electrolyte, ionic liquid, solid electrolyte) can be studied with in situ UV-Vis spectroscopy in various modes [i-iii] ... 

Gao, X., Jehng, J.-M. and Wachs, l.E. (2002) In situ UV-vis-NlR diffuse reflectance and raman spectroscopic studies of propane oxidation over Zr02-supported vanadium oxide catalysts. Journal of Catalysis, 209 (1), 43-50. 

Weckhuysen, B.M., Verberckmoes, A.A., Debaere, J., Ooms, K., Langhans, 1. and Schoonheydt, R.A. (2000) In situ UV-Vis diffuse reflectance spectroscopy-on line activity measurements of supported chromium oxide catalysts relating isobutane dehydrogenation activity with Cr-spedation via experimental design. Journal of Molecular Catalysis A Chemical, 151 (1-2), 115-31. 

The in situ UV-VIS spectroscopic measurement showed that upon adsorption of propene/benzene=l/6 mixture on HP at 295 K, bands at 210, 260 and 340 nm appeared (Fig. 8), whose intensities did change neither -with time nor upon evacuation at room temperature. When evacuation was performed at 373 K the band at 340 nm increased gradually, while at 473 K new bands appeared at 400-500 nm indicating the surface transformation became more complex. 

Often, the Rf value of the separated substances is compared with the Rf values of references. Not a long time ago, this information, together with the similar color, was usually enough to identify a substance. Today, modem densitometers are capable of measuring, more accurately, migration distances (therefore the Rf value) and to scan the in situ UV-Vis spectmm of the spot. 

ESMS [3]. In situ UV/vis spectra were measured photochemical cell through opti( flbers. 

In situ UV/vis spectra of TEOA-DMF solution containing under COj during irradiation (365 nm). Time interval is 20 s... 

Figure 21.5 The exterior and cross-section of the in situ UV-Vis cell [30],...

---