IR transmission cells

IR spectra of the samples were obtained in the range of 4000 cm to 900 cm by a Nicolet 710 (Nicolet Analytical Instmments) FT-IR spectrometer with a MCT detector. All spectra were recorded after 100 scans. A self-supporting disk of catalyst sample was mounted in a transmission IR cell. Prior to the methanol adsorption experiment the sample was dried under vacuum at different temperatures, then exposed to the methanol vapour for 60 minutes and dried under vacuum again. 

In-situ Infrared study of DMC, MPC and DMPD syntheses DMC, MPC and DMPD syntheses were studied in an in situ IR cell which was capable of operating up to 30 MPa. The solid catalyst sample was pressed into a self-support disk and placed between two Cap2 rods in the transmission IR cell. Table 1 lists reaction conditions for these synthesis reactions. Liquid reactant mixture (0.2 cm ) was brought into the IR cell by injection into a known amount of gaseous reactants flowing into the reactor cell. For the DMPD synthesis, the liquid reactant mixture was brought into IR cell via helium flow as a carrier. The... 

The catalyst for the in situ FTIR-transmission measurements was pressed into a self-supporting wafer (diameter 3 cm, weight 10 mg). The wafer was placed at the center of the quartz-made IR cell which was equipped with two NaCl windows. The NaCI window s were cooled with water flow, thus the catalyst could be heated to 1000 K in the cell. A thermocouple was set close to the sample wafer to detect the temperature of the catalyst. The cell was connected to a closed-gas-circulation system which was linked to a vacuum line. The gases used for adsorption and reaction experiments were O, (99.95%), 0, (isotope purity, 97.5%), H2 (99.999%), CH4 (99.99%) and CD4 (isotope purity, 99.9%). For the reaction, the gases were circulated by a circulation pump and the products w ere removed by using an appropriate cold trap (e.g. dry-ice ethanol trap). The IR measurements were carried out with a JASCO FT/IR-7000 sprectrometer. Most of the spectra were recorded w ith 4 cm resolution and 50 scans. 

Fixed pathlength transmission flow-cells for aqueous solution analysis are easily clogged. Attenuated total reflectance (ATR) provides an alternative method for aqueous solution analysis that avoids this problem. Sabo et al. [493] have reported the first application of an ATR flow-cell for both NPLC and RPLC-FUR. In micro-ATR-IR spectroscopy coupled to HPLC, the trapped effluent of the HPLC separation is added dropwise to the ATR crystal, where the chromatographic solvent is evaporated and the sample is enriched relative to the solution [494], Detection limits are not optimal. The ATR flow-cell is clearly inferior to other interfaces. 

One cm3 of the reactant/product/catalyst mixture was sampled periodically during the reaction for the transmission infrared analysis (Nicolet Magna 550 Series II infrared spectrometer with a MCT detector). The concentrations of reactants and products were obtained by multiplying integrated absorbance of each species by its molar extinction coefficient. The molar extinction coefficient was determined from the slope of a calibration curve, a plot of the peak area versus the number of moles of the reagent in the IR cell. The reaction on each catalyst was repeated and the relative error for the carbamate yield measured by IR is within 5%. 

Infrared transmission spectra were measured on self supported wafers (2 cm2, 20 mg), in a quartz IR cell allowing sample heating under vacuum and introduction of standardised volumes of gas. The samples were activated under vacuum (106 torr) by heating (1 K.min 1) up to 673 K. 

Within the IR spectroscopy arena, the most frequently used techniques are transmission-absorption, diffuse reflectance, ATR, specular reflectance, and photoacoustic spectroscopy. A typical in situ IR system is shown in Fig. 7. Choosing appropriate probe molecules is important because it will influence the obtained characteristics of the probed solid and the observed structure-activity relationship. Thus, the probe molecules cover a range from the very common to the very rare, in order to elucidate the effect of different surfaces to very specific compounds e.g. heavy water and deuter-ated acetonitrile, CDsCN). The design of the IR cell is extremely important and chosen to suit the purposes of each particular study. For catalytic reactions, the exposure of catalytic metals must be eliminated in cell construction, otherwise the observed effect of the catalyst may not be accurate. 

A powerful characteristic of the cell described above is the opportunities it affords for the determination of the compositions of both the lower (denser) and upper (lighter) phases. In particular, the combination of ATR and transmission IR spectroscopy shows the distribution of the catalyst between the two phases. For example, in the homogeneously catalyzed formylation of morpholine with carbon dioxide and hydrogen by a ruthenium catalyst, a two-phase system was found at a... 

For IR measurements, the zeolite powders were pressed into self supporting wafers which were activated by heating in He flow (20 ml/min) up to 773 K with a rate of 10 K/min. During all treatments, the samples were analyzed in situ by means of transmission absorption IR spectroscopy using a Bruker IFS88 FTIR spectrometer The IR cell was constructed as continuously stirred tank reactor (volume=l. 5 cmJ) equipped with 1/16" gas in- and outlet... 

A new apparatus for transmission IR measurement has been built based on the design of Basu and Yates. The IR cell consists of a stainless steel sphere with six 2.75 inch conflate flange ports. The IR beam enters and exits the cell through two differentially pumped KBr windows. The cell is pumped with a roughing pump to maintain a base pressure < 2.0 - 5.0 x 10 Torr. The front part of the IR cell is connected to a six-way cross with ports for gas dosing, pumping, and... 

IR spectroscopy was mainly used to characterize the sorbed species. The zeolite powder was pressed into self supporting wafers and analyzed in situ during all treatments (i.e., activation, sorption, reaction) by means of transmission absorption IR spectroscopy using a BRUKER IPS 88 FTIR spectrometer (resolution 4 cm" ). For the sorption experiments, an IR cell equipped with IR transparent windows which could be evacuated to pressures below 10" mbar was used [11]. The activated zeolite wafer was contacted with a constant partial pressure (0.001 mbar) of the adsorbate at 308 K until adsorption-desorption equilibrium was reached (which was monitored by time resolved IR spectroscopy). For the coadsorption experiments, the catalysts were equilibrated with 0.001 mbar of both adsorbates admitted in sequentional order. The spectra were normalized for the sample thickness by comparing the intensities of the absorption bands of the adsorbate with the integral intensity of the lattice vibration bands of the zeolite between 2090 and 1740 cm". The surface coverage was quantified by calibration with gravimetric measurements (under conditions identical to the IR spectroscopic experiments). 

Transmission IR studies were performed with a conventional cell made... 

In a similar manner to the lightpipe in GC-IR, a flow cell interface can be used where the eluent flows into a transmission flow cell with IR windows at each end and the IR beam passes through the cell perpendicular to the flow and continuously records IR spectra. This only works if the solvents do not absorb so strongly in the IR region of interest and mask the analyte transmission/absorption, or if the mobile phase absorption spectrum is subtracted (which only works well when the LC method is isocratic). In fact, the solvents used in normal phase HPLC are more compatible with IR than the more polar ones used in reversed phase HPLC. 

---