Cells, spectroscopic

After introduction of the working electrode to the spectroelectrochemical cell, continuous potential cycling was performed to obtain a clean surface before each 

SFC Study of the Potential-Dependent Structure ofWater at a Pt Electrode/Electrolyte Solution Interface 

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

we demonstrate the usefulness of SFG spectroscopy in the study of water structure at electrode/electrolyte solution interfaces by showing the potential dependent SFG spectra in the OH-stretching vibration region at a Pt/thin film electrode/0.1 M HGIO4 solution interface in internal reflection mode. 

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Figures 7.9(a) and 7.9(b) show two different approaches to the samphng of the dissolution baths prior to analysis. Figure 7.9(a) shows the most commonly installed system, which uses a series of spectroscopic cells, one to coincide with the hath being sampled. The system uses a peristaltic pump to withdraw the sample through the pump tubing and into...

The primary contributions to pressure drop, in approximately decreasing order, will be (1) inline filters (2) needle valves (3) check valves (4) the spectroscopic cells and (5) capillary tubing. Methods for detailed calculations can be found in Ref [21]. Our experience is that total recycle pressure drop is a small fraction of a bar with normal flow rates. 

Some controversy surrounds the usage of the term in situ. Some researchers even go so far as to suggest that unless a reactor and spectroscopic cell/probe are one and the same unit, the measurement cannot be in situ. The results of Section 4.3.1 suggest otherwise. If the fluid elements in the cell are compositionally similar to the fluid elements in the CSTR and are at similar temperature and pressure, then they are indistinguishable. The measurements are in situ. With proper care regarding transport effects, and reaction considerations, an experimental apparatus with a configuration like Figure 4.1 provides in situ spectroscopic capability for dark reactions. 

Many catalytic reactions require high pressures of reactant gases. Thus, an in-depth understanding of such catalytic systems requires truly in situ NMR and IR measurements and it has been necessary to develop appropriate High Pressure-spectroscopic cells the development and use of HP-NMR and HP-IR cells are reviewed in chapters 2 and 3 respectively. The use of both of these complementary methods/HP-techniques is probably best illustrated in chapters 5 - carbonyla-tion reactions, chapter 6 - hydroformylation and chapter 7 - alkene/CO copolymerisation, which deal with the recent advances in each of these important areas. 

I hope this volume will transfer some important aspects of NMR and IR, including the use of HP-spectroscopic cells for measurements under actual reaction con-... 

The contrast factors have been measured interferometrically [87] and with an Abbe refractometer, respectively. The sample is contained in a fused silica spectroscopic cell with 200 pm thickness (Hellma). The sample holder is thermostated with a circulating water thermostat and the temperature is measured close to the sample with a PtlOO resistor. The amplitude of the temperature modulation of the grating is well below 100 pK and the overall temperature increase within the sample is limited to approximately 70 mK in a typical experiment [91], which is sufficiently small to allow for measurements close to the critical point. 

Place your sample in a 1-cm length quartz spectroscopic cell. The control (blank) spectroscopic cell should contain absolute ethanol. Read the absorbance of your sample against the blank, according to the instructions of your spectrophotometer, at 325 nm. Record the absorption at 325 nm on your Report Sheet (5). 

Meunier FC. The design and testing of kinetically-appropriate operando spectroscopic cells for investigating heterogeneous catalytic reactions. Chem Soc Rev. 2010 39 4602. 

Among the requirements that have to be considered in the design of spectroscopic cells for Raman experiments in controlled environments are the following ... 

Thus, activity and kinetics data and activation energy values measured with such a spectroscopic cell have to be consistent with those obtained with corresponding conventional catalytic reactors. 

A criterion for the suitability of a spectroscopy cell for investigations of working catalysts can be formulated as follows the activity or selectivity data and activation energy values have to be in agreement with the catalytic performance data measured with a conventional fixed-bed reactor. Table 1 is a comparison of the conversion and selectivity values characterizing an alumina-supported molybdenum-vanadium oxide catalyst during propane ODH obtained with a conventional fixed-bed reactor and with a spectroscopic cell that fulfills this requirement (Banares and Khatib, 2004). Similar considerations have also been reported earlier for other methods, such as X-ray diffraction (Clausen et al., 1991). 

Lunsford and coworkers (Xie et al., 1999) reported kinetics data characterizing the catalytic NO decomposition measured in their Raman cell. Other attempts were made by Volta and coworkers (Abdelouahab et al., 1992), but only low conversions were reached for alkane oxidation because of significant temperature gradients (Volta et al., 1992). The cell designed by Stair (2001) appears to be suitable for simultaneous determination of spectra and catalytic activity. Several groups have addressed the issue of obtaining accurate catalytic performance data when the reactor is a spectroscopic cell (Banares and Khatib, 2004 Guerrero-Perez and Banares, 2002 Kerkhof et al., 1979 Mestl, 2002). 

The coupling of a microreactor array in combination with an X-ray camera was used by Grunwaldt et al. (2007) to record the XAFS spectra of ten catalysts simultaneously. In this feasibility exercise, the arrangement comprised a spectroscopic cell with ten sample compartments (2 or 5 mm in thickness) that were filled with meshed and sieved catalyst particles. There was little detail provided about the heating and gas flow arrangement, but the cell could be heated (although the preliminary data were all recorded after flowing either a Ff2 helium or Cb—helium mixture at room temperature). 

Normally the rate of this secondary reaction is slow, and UCle is not contaminated with UF4, but in larger-scale preparations, if heat is not adequately dissipated, the rate of the secondary reaction can become considerable. In these circumstances the UCle will be contaminated with UF4. For larger-scale preparations apparatus must therefore be designed to dissipate rapidly the heat released. It should also be noted that with this preparative method it is often convenient to prepare the UCle in situ, e.g., within a spectroscopic cell. This can completely eliminate handling and consequent contamination of the UCle-... 

Hannemann, S., Casapu, M., Grunwaldt, J.-D., Haider, P., Triissel, P., Baiker, A. and Welter, E. (2007) A versatile in situ spectroscopic cell for fluorescence/ transmission EXAFS and X-ray diffraction of heterogeneous catalysts in gas and liquid phase. J. Synchrotron Rad., 14, 345—354. 

Fig. 2. High pressure reactors and spectroscopic cells as used at the Max-Planck-Institut fiir Kohlenforschung for exploratory studies on chemical synthesis in seCOj...

The transition metal ion-containing films were prepared carefully by ion-exchange as described elsewhere (10-16). These films were mounted in appropriate stainless steel or pyrex glass reactors/spectroscopic cells. Both reactors, described in detail elsewhere, had infrared (KBr) or uv-vis (quartz) transmitting windows for spectroscopic studies. They were equipped with vacuum valves for evacuation and gas admission, a heating system and a temperature monitor. 

With the NMR tube, chemists were offered a lighter and subtler perturbation. The reagent now consisted only of radiofrequencies (RF). Their resonant absorption by the sample in the NMR tube yielded a comprehensive inventory of the groups of atoms present. The NMR tube did not alone replace the test tube, because it came at the heels of other spectroscopic cells, such as for electronic absorption (UV-visible) or in vibrational (IR and Raman) spectroscopy. 

Initially, photochemical studies were performed in a miniature spectroscopic cell which was designed with a low volume (ca. 1 mL), to minimize stored potential energy and to permit safe operation on the open bench. This modular... 

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