Sorption zeolite powder

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). 

Zeolite powder has the lowest flowability of all detergent powder components. Bridging in the silos and screwers is a common event. An improvement can be obtained by modifying the surface by sorption of different additives (e.g.. Silanes [57]), or modifying the surface as early as the induction period, as was discussed above. 

Small amounts of water within a zeolite can have a large effect on some experiments, so complete dehydration is often necessary. A zeolite which is to be exposed to alkali-metal vapor, for example, must not be given an opportunity to resorb water fi-om other parts of its vessel after dehydration but before metal vapor sorption. The resulting metal hydroxide or oxide (additional products) could lead to the destruction of the zeolite. To compound the problem, the experimental conditions are often not described in detail in a report in the literature, so the reader can only be suspicious of a link between the reported result and inadequate dehydration. For some work, involving large amounts of powder, this problem may sometimes be of minor importance. Where tiny samples are involved, it is crucial. 

Parise JB, Chen J (1997) Studies of ciystalhne solids at high pressure and temperature using the DIA multianvil apparatus. Eur J Solid State Inorg Chem 34 809-821 Parise JB, Coibin DR, Abrams L (1995) Stractural changes upon sorption and desorption of Xe from Cd-exchanged zeolite rho A real-time synchrotron X-ray powder diffraction study. Microporous Mater 4 99-110... 

In the preceding chapter it had already been discussed that it is less the synthesis itself which may be the bottleneck in high-throughput zeolite science but rather the analysis of the solids formed in a high-throughput program. There are several standard characterization techniques which are typically employed to characterize zeolitic materials. These include powder XRD for phase identification, X-ray fluorescence analysis (XRF) or atomic absorption spectrometry to analyze elemental composition, sorption analysis to study the pore system, IR-speclroscopy, typically using adsorbed probe molecules to characterize the acid sites, NMR spectroscopy and many others. For some of these techniques parallelized solutions have been developed and described in the literature, other properties are more difficult to assess in a parallelized or even a fast sequential fashion. 

Zeolites of type Y are prepared by either primary or secxindary synthesis. Structures include zeolite Y in t)oth the cubic and hexagonal forms, SAPO-37 and faujasitic frameworks containing Ga or Zn. These materials are characterised using solid state NMR, X-ray powder diffracticai, infrared jectrosccpy, surface aneilysis and sorption. Catalysts are then evaluated for the conversion of n-hexane, cyclohexane and gas-oil. Results are interpreted in terms of the effectiveness of catalytic sites in alkane activaticxi and in the effect of both density and distribution of active sites. 

Synthetic zeolites produced by scientists at Union Carbide Corp. from sodium-bearing systems were shown by powder x-ray methods to have the same framework topology as that of the mineral faujasite (2, 19), and furthermore, the sorption characteristics were consistent with the geometry of the framework. Types Y and X zeolite were distinguished on the basis of various chemical and physical properties (18) such that the former ranges from 48 to 76 A1 atoms per cell and the latter from 77 to 96. Most measurements have been made on Y with about 58 atoms per cell and X with about 88 A1 atoms per cell. The range for Y encompasses the Al-content for natural faujasite which is near 59 atoms per cell, though some variation may occur in faujasite specimens. 

X-ray powder diffraction (XRPD), thermo gravimetric (TGA) analysis, solid-state nuclear magnetic resonance (NMR), and measurements of adsorption isotherms are key methods for characterizing zeolite-like behavior. However, a simple proof for observing structural changes during the sorption processes is XRPD. 

Dry mixing technology brought to center stage surface properties and powder particle interaction forces. The consequences were zeolite surface charges and sorption properties became as important as, for example, lEC. 

Propene and propane sorption uptake by a powder sample ofZIF-8 (Zn-methylimidazolate). Reproduction from Li K, Olson DH, SeidelJ, Emge TJ, Cong H, Zeng H, et al. Zeolitic imidazolate frameworks for kinetic separation of propane and propene. J Am Chem Soc 2009 31 10368-9, with permission. 

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