Sorption pressed wafers

Besides the possibility to study sorption kinetics in angle crystals which nuy not be pressed into self-supporting wafers, IR microscopy requires only tiny amounts of sample, ca. 10 mg in comparison to 10 mg in the conventional IR technique. 

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). 

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