Drift cell

Characterization. In-situ diffuse reflectance FTIR (DRIFT) experiments were carried out with undiluted samples of the zeolites in a Spectratech DRIFT cell and a Nicolet Magna 550 spectrometer. Most experiments were carried out in a flow mode, passing 0.84 ml/s of a gas mixture containing inert (He, Ar or N2) and N2O, NO, CO or mixtures of these gases continuously through the cell at atmospheric pressure. Each spectrum was recorded by addition of 256 scans and a resolution of 8 cm. ... 

For the DRIFTS study, the Nafion-Ti02 slurries were sonicated for 2 hours, dried at ambient conditions for 5 hr, and ground with a pestle and mortar until a fine powder catalyst was formed. 30 mg of the resulting catalysts were placed on top of 80 mg of inert CaF2 powder (325 mesh, Alfa Aesar) in a DRIFTS cell s sample holder. The sample holder was enclosed by a dome with two IR transparent ZnSe windows and a third CaF2 window for UV illumination. For the ATR study, the Nafion-Ti02 slurries, which were sonicated for two hours, were cast directly on the surface of the ATR ZnSe crystal to form a continuous solid film. The films were enclosed with a stainless steel cover equipped with a CaF2 window for UV illumination. 

Figure 52.1. Single beam IR spectra of the Pl/Ti02 catalyst on the DRIFT cell before and after introducing ethanol, and during UV illumination.

Figure 52.2. Difference spectra of the Pt/Ti02 catalyst on the DRIFTS cell during UV illumination.

Figure 52.5. Difference spectra of a 1 1 Nafion Ti02 weight ratio catalyst on the DRIFTS cell during UV illumination. Difference spectra was obtained by subtracting the spectram at 0 min (i.e., before the reaction starts) from the subsequent spectra.

The tubular reactor consists of a stainless steel tube (3/8 OD) in which approximately 300 mg of 2% Rh/Al203 is held in place with glass wool and 22 mg of catalyst is loaded in DRIFTS cell. The temperatures are monitored with a K type thermocouple connected to an omega temperature controller. Both pulse and step reaction studies were carried out at 250 °C. 

DRIFT spectroscopy was used to determine Av0h shifts, induced by adsorption of N2 and hexane for zeolite H-ZSM-5 (ZSM-a and ZSM-b, Si/Al=15.5 and 26), H-mordenite (Mor-a and Mor-b, Si/AI— 6.8 and 10) and H-Y (Y-a and Y-b, Si/Al=2.5 and 10.4) samples. Catalysts were activated in 02 flow at 773 K in situ in the DRIFTS cell and contacted than with N2 at pressures up to 9 bar at 298 K or with 6.1% hexane/He mixture at 553 K, i.e., under reaction conditions. Catalytic activities of the solids were measured in a flow-through microreactor and kapp was obtained as slope of -ln(l-X0) vs. W/F plots. The concentration of Bronsted acid sites was determined by measuring the NH4+ ion-exchange capacity of the zeolite. The site specific apparent rate constant, TOFBapp, was obtained as the ratio of kapp and the concentration of Bronsted acid sites. 

The device resembles a cylindrical differential mobility analyzer (DMA) in that a sample flow is introduced around the periphery of the annulus between two concentric cylinders, and charged particles migrate inward towards the inner cylinder in the presence of a radial electric field. Instead of being transmitted to an outlet flow, the sample is collected onto a Nichrome filament located on the inner cylinder. The primary benefit of this mode of size-resolved sampling, as opposed to aerodynamic separation into a vacuum, is that chemical ionization of the vapor molecules is feasible. Because there is no outlet aerosol flow, the collection efficiency is determined by desorption of the particles from the filament, chemical ionization of the vapor, separation in a mobility drift cell, and continuous measurement of the current produced when the ions impinge on a Faraday plate. 

Infrared spectroscopy of adsorbed CO is a useful characterization tool for dendrimer-templated supported nanoparticles, because it directly probes particle surface features. In these experiments, which are performed in a standard infrared spectrometer using an in-situ transmission or DRIFTS cell, a sample of supported DENs is first treated to remove the organic dendrimer. Samples are often reduced under H2 at elevated temperature, flushed with He, and cooled to room temperature. Dosing with CO followed by flushing to remove the gas-phase CO allows for the spectrum of surface-bound CO to be collected and evaluated. Because adsorbed CO stretching frequencies are sensitive to surface geometric and electronic effects, it is potentially possible to evaluate the relative effects of each on nanoparticle properties. 

Diffuse reflectance IR spectroscopy has become an attractive alternative to mulls with the introduction of DRIFT cell by Griffiths,29 later modified by Yang.30 Since materials are dispersed in a nonabsorbing medium and not subjected to thermal or mechanical energy during sample preparation, DRIFT spectroscopy is especially suitable for the qualitative/quantitative analysis for polymorphs, which are prone to solid-state transformations. The Kubelka-Munk (K-M) equation,31 which is analogous to Beer s law for transmission measurements, is used to quantitatively describe diffusely-reflected radiation ... 

Enamine basicity has been investigated exclusively by the ICR technique, one of the most salient features of which is the low working pressures usually employed (between 10- 7 and 10- 4 torr). Drift-cell instruments allow the ion-molecule reaction to develop with thermalization of the species involved in the equilibrium in a few milliseconds at a pressure of ca 10- 4 torr. Trapped-ion cell instruments afford reaction times of up to... 

Ions exiting the drift tube are mass analyzed in mass spectrometer MS2, an important feature if reactions are occurring in the drift cell. Ions are generally detected after MS2 by ion counting techniques. The mass spectrometers MSI and MS2 are typically quadrupole mass filters, and either one or the other can be run in RF-only mode for better signal but without mass selection, if desired. 

Fig. 2. Perspective cross sectional view of the temperature controlled drift cell after Kemper and Bowers design [22] (a) cooling line, (b) cell body, (c) buffer gas inlet, (d) cell end cap, (e) drift guard ring, (f) ion entrance hole, (g) ion focusing lens, (h) ceramic ring, (i) ion exit hole, (j) ceramic rod holding guard rings, (k) ceramic rods holding cell assembly...

Fig. 5. a Mass spectra of l-serine obtained after ions spent -200 ps in the drift cell at the temperature indicated. With increasing temperature first the trimer (ser)3H+ and then the dimer (ser)2H+ disappear from the spectrum Relative intensities of peaks corresponding to sodiated species (marked with ) are not reproducible, b 334 K ion arrival time distribution (ATD) of dimer ions exiting the cell (m/z=211). c 464 K ATD of serine monomer (m/z=106)... 

Kemper PR, Bowers MT (2002) Instrumental paper on TOF-drift cell-quad setup (to be published), see also [17,18]... 

Schlager H., Fabian R. and Arnold F., A new cluster ion ion source / ion drift cell apparatus for atmospheric ion studies - First mobility and reaction rate coefficient measurements. In Proc. 3rd Intern. Swarm Seminar, 3-5 Aug. 1983, Innsbruck, 257-262 (1983). 

We have recently developed a gas-phase ion chromatography technique and applied it to carbon cluster cations " " and anions""". A pulse of mass-selected cluster ions is injected into a high-pressure drift cell filled with 2-5 torr of helium. The ionic mobilities of different isomeric structures depend on their different collision cross-sections with He, and the isomers are therefore separated while drifting through the cell, under the influence of a weak electric field. The absolute value of the ionic mobility for a given cluster together with computer simulations often allows unambiguous determination of the cluster... 

The DRIFTS studies were carried out at different temperatures on a Nicolet 20 SXB FTIR spectrometer equipped with a commercial DRIFTS catalytic chamber and associated hardware from Spectratech . The DRIFTS cell is a temperature-controlled flow-through reactor. Upon calcination, samples were cooled to room temperature under nitrogen. Subsequently, 25 microliters (liq.) of the chosen alcohol were injected and spectra were collected at 373, 473, 623 and 773 K during the heating cycle. A spectral resolution of 4 cm was used. 

Coupled measurements of the catalytic activity by monitoring the gas composition at the DRIFT cell outlet, indicate a slight decrease of the activity for the INi sample and a slight increase for DPNi within the 15 h of reaction, in agreement with the results obtained during the same period with the conventional catalytic test (Fig. 1). 

Fig. 1.21. Schematic layout of the ion mobility instrument employed in metal cluster ion studies. The setup consists of different cluster sources housed in a source chamber, a time-of-flight mass spectrometer, a helium filled drift cell, and a quadru-pole mass filter for final ion detection (from right to left). Also displayed is an ion trajectory simulation of cluster ions of a mass of 500 amu drawn through the helium filled (7 mbar) drift cell at 300 K. The simulations show that under these conditions roughly 1% of the ions hnally escape through the 0.5 mm diameter exit hole [137]...

The metal supported catalysts were characterized by FTIR spectroscopy, TEM analyses, surface area and metal dispersion determinations. The 5% Ru/Nb205 catalysts, discharged after the activity tests, were subjected to pulse NO chemisorption in a ZnSe DRIFTS cell at 423 and 523 K. 

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