Supports discs

FT-IR spectra were recorded at RT on a Perkin-Elmer 1760-X spectrophotometer equipped with a cryodetector, at a resolution of 2 cm-" (number of scans -100). In the 1070-960 cm- region, band integration and curve fitting were carried out by Curve fit, in Spectra Calc. (Galactic Industries Co.). Powdered materials were pelleted in self-supporting discs of 25-50 mg cm-2 and 0.1-0.2 mm thick, placed in an IR cell allowing thermal treatments in vacuo or in a controlled atmosphere. 

FTIR spectra were collected with a Nicolet 740 spectrometer and a custom built in situ gas flow cell. The spectrometer was equipped with a MCT-B detector cooled by liquid nitrogen. Approximately 15 mg of the MgO catalyst sample was pressed into a self-supported disc and placed in a sample holder located at the center of the cell. The temperature in the cell was measured with a thermocouple placed close to the catalyst sample. Transmission spectra were collected in a single beam mode with a resolution of 2 cm 1. Prior to introduction... 

The FT-IR measurements were carried out in a Nicolet IRTF spectrometer. Samples (self-supported discs) were activated in situ under vacuum (10 6 mbar) at 450°C before adsorption of probe molecules. Adsorption was carried out at room temperature the physisorbed species were removed at RT (C02) and 150°C (2,6-dimethylpyridine) under vacuum. 

The ESR measurements were conducted after evacuation of the catalysts at various temperatures (RT to 723 K) and after NO adsorption at RT. ESR spectra were recorded at 77 K on a RADIOPAN SE/X 2547 spectrometer. The patterns were obtained at vESR = 8.9 GHz FTIR study was performed using a VECTOR 22 (BRUKER) spectrometer The self supported discs of 10 mg cm 2 of the catalysts were activated under vacuum at 723 K Pyridine was admitted at RT and after saturation the samples were degassed at RT, 423, 523, and 623 K in vacuum for 30 min. 

FTIR spectra woe recorded at RT with a Nicolet 5ZDX spectrometer, uang a resolution of 4 cm and taking 128 scans for ev spectrum. Thin self-supporting discs (ca. 10 mg cm V prepared by pres g the powdos, were handled in standard greaseless cells, where they could be subjected to thermal or adsorption treatments. 

X-ray dififaction studies were carried out with Phillips PW 1140 X-ray diffractometer, using Ni-filtered Fe K radiation. FTIR spectra of the catalysts were recorded on Nicolet-740 FTIR spectrometer. Self supporting discs were prepared from KBr and the catalyst mbrture applying pressure. These discs were used for recording FTIR spectra. 

A, had cell B, speed control for the motor drive C, support bar (a hole in this served as the confining chamber) D, support disc used to secure the load cell to the apparatus. (This initial load on the load cell—i.e., before compression—was regulated by adjusting the tension in these screws.) E, displacement transducer F, motor-driven micrometer screw G, power supplies for the load cell and the displacement transducer H, recorder. 

For IR measurements, the sample was pressed into self-supporting discs ( 10 mg.cm ). The spectra of the adsorbed species were obtained by subtracting tire spectrum of the wafer from the spectrum obtained after adsorption. 

XRD patterns were recorded on a Philips PW 1710 instrument using Cu K i radiation (A. = 0.15418 A, 40 kW, 25 mA). N2 sorption experiments at 77 K were carried out with a Sorpty 1750 instrument (Carlo Erba Strumentazione) and specific surface areas (SS) calculated using the BET method (Table 1). Absorption/transmission IR spectra were run at RT on a Perkin-Elmer FT-IR 1760-X spectrophotometer equipped with a Hg-Cd-Te cryodetector. For IR analysis powders were pelletted in self-supporting discs (10-15 mg cm ), activated in vacuo at increasing temperature up to 823 K, heated in dry O2 at the same temperature and cooled down in oxygen or subsequently reduced in H2 at 623 K and outgassed at the same temperature. CO and NO (Matheson C.P.) were used as probes. 

The most common method which has been used to record the IR spectmm of silica has been to compact a high surface area sifica (200 to 300 m /g) into a self-supporting disc which contains from 5 to 10 mg of SiOa per cm. By using this preparation technique the disc can then be conveniently mounted in a suitable evacuable chamber where subsequent vacuum activation can be carried out in order to remove adsorbed water or other contaminants, and adsorption experiments at the gas-solid interface can easily be carried out. 

This paper will only be concerned with the surface chemistry of silica in vacuum and/or in the presence of an adsorbate. The IR spectrum of a typical self-supporting disc of a pyrogenic or fumed sifica after heating under vacuum for 1 h at 150 C is shown in Figure 25.1 A. Pyrogenic or fumed silicas [some trade names are AerosU and Cab-O-Sil] are made by the flame hydrolysis of SiCLt at 1000°C. These non-porous silicas have a low bulk density and adsorbed water can be removed by evacuation at 20°C. However, the spectral properties are identical when evacuation is carried out at 150 C evacuation at the latter temperature is preferred in order to remove any trace impurities which may be present. The spectrum is characterized by a sharp absorption band at 3747 cm with a broad tail to low wavenumber having a maximum near 3550 cm . The sharp peak is due to the OH... 

FIGURE 25.1 A, IR spectrum of a self-supporting disc and B, a thin film of Si02 after heating under vacuum at 150°C for 1 h. 

The P=0 and SiOP modes could never be detected using a self-supporting disc of Si02, and this example serves to illustrate the utility and methodology behind the thin film, or TF technique. 

The reaction at room temperature with the accessible SiOH groups on silica is over in less than 60 seconds when excess TiCla is in contact with a self-supporting disc of Si02 [11]. 

An unexpected result was the progressive apparent dechlorination of SiOTiCla. We have verified that this phenomenon was not related to the presence or absence of TiCU either physically adsorbed or in the gas phase. We could also observe the growth of the same IR bands between 1000 and 600 cm using a self-supporting disc. Therefore, the dechlorination of TiCU on silica and the eventual incorporation of Ti as a random mixed metal surface oxide is probably entropy driven. Although the initial chemisorption follows reaction (3) and (4), further dechlorination probably results in the formation of SiCl surface species. The vibrations of this near 7(X) cm would be impossible to detect with a thin film given the low extinction coefficient [15], and in any case, they would be masked by the much stronger SiOTi vibrations. Finally, the results have implications for mixed oxide catalysts which are prepared by chemical vapor deposition. Structural models which are based on the notion that only reactions like those depicted in schemes (3) and (4) occur are probably not valid. 

X 10 , 3.1 X 10 and 6.8 x 10 sec " for angular velocity of a supporting disc 240, 270, 300 and 330 rpm, respectively. However, although Johnson-Mehl-Avrami equation satisfactorily describes overall kinetics, it is hard to give any unambiguous physical interpretations of the derived values of Avrami exponent, n which varies from 2.14 to 3.57. 

The supported ionic liquid membranes (SILMs) were prepared by depositing the ionic liquids [hmim][Tf2N] and [H2NC3H6mim][Tf2N] on top of cross-linked nylon support discs in a shallow glass container. A sufficient amount of ionic liquid to cover the membrane was used. The membrane was allowed to absorb the ionic liquid for at least 4 hours, and then the SILMs were removed from container and blotted dry. Further details concerning this procedure were published earlier [19]. 

Supported disc-reagents were prepared for acylation of several amines in a flow system (113), affording very good conversions into the corresponding amides (114). 

The most common technique in practice, to obtain a good spectrum of the fundamental vibrations of a powdered insulating material with the transmission/absorption IR technique, is to prepare a layer appropriately diluted and sufficiently thin. To do this the most used technique is that of the KBr pressed discs. KBr in fact is an easily available powdered material which does not absorb in the medium IR region (down to near 400 cm i.e. it cuts out the far IR). It can be easily mixed homogeneously with the powder to be investigated, and pressed, thus obtaiiung diluted self-supporting discs very useful for IR transmission. Other materials (such as e.g. Csl or polyethylene for far IR studies) allow the production of similar pressed discs, with cut-off limits at even lower frequencies. Alternatively, the powders can be... 

The in situ characterization of a solid surface by FT-IR is a well known and current method of investigation in a number of laboratories. Nevertheless, each team of scientists may use different analysis techniques. In our case we choose the transmission technique, so that samples are pressed (10 Pa) into self-supported discs (2cm area, 7-lOmg cm ). They are placed in a home-made quartz cell equipped with KBr windows (Figure 4.5). 

The other one, a spherical support, is formed by a spherically faced surface of the support disc, mounted in the back face of the thrust pad. Spherical support configuration is often preferred due to the ability of the pad to tilt not only in the direction of rotation but also in the radial direction. The latter provides some compensation for misalignment between the thrust bearing face and the collar. On the other hand, the radial rib support reduces radial elastic pad distortion and does not require hardening. Spherical pivots must be hardened because of high contact stresses at the pad pivot [7]. 

---