Na-X zeolite

Deuterium NMR has recently been used to study molecular motion of organic adsorbates on alumina (1.) and in framework aluminosilicates (2). The advantage of NMR is that the quadrupole interaction dominates the spectrum. This intramolecular interaction depends on the average ordering and dynamics of the individual molecules. In the present work we describe NMR measurements of deuterated benzene in (Na)X and (Cs,Na)X zeolite. 

A Na-X zeolite (cubic symmetry) has an XRD pattern as shown below. Calculate the lattice constant a of this zeolite from the 20 positions of the reflections. The wavelength of the x-rays is X = 0.154056 nm (Cu Ka radiation). 

Tphe isomerization of olefins over acidic catalysts has been carefully A studied in the past few years. Hightower and Hall (1, 2) have studied the isomerization of n-butenes over silica-alumina. They were able to interpret their results in terms of a simple model involving the 2-butyl carbonium ion as a common intermediate. More recently Lombardo and Hall studied the isomerization of the same olefins over Na-Y-zeolite. They showed that the reaction was first order in conversion as well as time (3), that the isomers could be directly interconverted (4), and that activity sharply increased with water addition reaching a saturation value (5). There are, however, reports in the literature which are at variance with this idea. Dimitrov et al. (7, 8) explained their results for n-butene isomerization on Na-X-zeolite in terms of a free radical type mechanism. As discussed more thoroughly elsewhere (4) others have argued about the nature of catalytic activity on zeolites (9-13). 

Thermodielectric experiments were performed using the Na-X zeolite (Si/Al = 1.25 provided by Laporte, London, UK). Within the framework of the cavities of the Na-X zeolite, the following were adsorbed water(withadielectricconstante=78.5at25°C), acetone... 

The home-made heat-flow calorimeter used consisted of a high vacuum line for adsorption measurements applying the volumetric method. This equipment comprised of a Pyrex glass, vacuum system including a sample holder, a dead volume, a dose volume, a U-tube manometer, and a thermostat (Figure 6.3). In the sample holder, the adsorbent (thermostated with 0.1% of temperature fluctuation) is in contact with a chromel-alumel thermocouple included in an amplifier circuit (amplification factor 10), and connected with an x-y plotter [3,31,34,49], The calibration of the calorimeter, that is, the determination of the constant, k, was performed using the data reported in the literature for the adsorption of NH3 at 300 K in a Na-X zeolite [51]. 

Figure 8.27 shows an actual Nyquist plot (negative of the imaginary part of the complex impedance, Zj versus the real part of the complex impedance Zr) obtained by measuring the impedance of a NilNa-X INi02 battery, which is composed of a wafer (with a diameter of 12mm) in which were sandwiched films of Ni powder (0.5 g), Na-X zeolite powder (0.5 g), and Ni02 powder (0.5 g) [132],... 

A number of papers dealing with this topic have been published since the first review paper appeared in 1987, like the experimental evidence for the self-consistency of the NMR diffusion data obtained by using the H- and NMR spectroscopy to investigate the selfdiffusion of CHF2CI in Na X zeolite by varying the intensity of the external magnetic field... 

Goldfarh D and Kevan L (1986), Reduction and oxidation effects on rhodium species in Na-X zeolite studied hy electron spin echo and electron spin resonance spectroscopies , J Phys Chem, 90, 2137. 

Sherry (56, 57) showed that the ion-exchange properties of Na-Y and Na-X zeolite were consistent with 16 Na atoms in the sodalite cage. Since Na scatters x-rays rather similarly to H20 molecules, the presence of 16 Na atoms is consistent with the electron density measurements. 

The epoxy-alcohol (15) (76%) was obtained from (14), using the cyclo-pentadienyl-vanadium catalyst [(CsH5)V(CO)4] in solution at 50°C. Under similar reaction conditions, a catalyst prepared by exchange of V and Cu with an Na-X-zeolite resin furnished a mixture of (15) and (16) in 46% and 40% yields respectively. ... 

Related Ru systems have been prepared on Na X-zeolite. While these were active for the hydroformylation of ethene at 10 MPa and 200 °C, appreciable amounts of products from competing ethene dimerization or Fischer-Tropsch reactions were also observed and significant Ru elution occurred. 

Fig. 2 a System for surface temperature infrared (STIR) measurements, b Transient temperature response upon methanol sorption into Na-X zeolite as a function of the square root of time [17]... 

Fig. 12 Diffusivities of linear alkanes in different zeolites obtained at 475 K as a function of the carbon number a self-diffusivities derived from PPG NMR in Na-X zeolite, b self-diffusivities measured by QENS in ZSM-5, c transport diffusivities obtained by NSE in 5A [48]...

Table 5. Approximate assignments of observed iattice vibrational frequencies of Na-X zeolite [246] based on calculations [113]...

Cs-Na-X zeolite and Cs-B carbon show 96% selectivity to ethyl benzene... 

Shigemoto N., Hayshi H., Miyaura K. Selective formation of Na-x zeolite from coal fly ash by fusion with sodium hydroxide prior to hydrothermal reaction. /. Mater. Sci., 1993 28 4781-4786. 

Gusev, V.Y., and Fomkin, A.A., Thermodynamics of high-pressure Tian-Calvet adsorption calorimetry and the heats of adsorption of Xe on Na-X zeolite over the temperature range 229-467K, Adsorpt. Sci. Technol., 8(2), 75-85 (1992). 

Papurello et al. [29] reported the use of with Na-X zeolites combined with a ZnO guard bed (heated at 300 °C) before feeding the reformer unit in order to guarantee a durable and stable operation. 

Fig. 9 Calorimetric differential molar heats of adsorption of various probe molecules versus coverage for Na-X zeolite ammonia (x from [65], activation at 673 K, adsorption at 308 K), water ( , activation at 593 K, adsorption at 298 K), methanol ( , activation at 623 K, adsorption at 298 K), benzene (+, activation at 623 K, adsorption at 298 K), and p-xylene (0, activation at 623 K, adsorption at 303 K)...

As a final example. Fig. 9 presents the differential heats of adsorption of ammonia, p-xylene, benzene, methanol, and H2O at about 300 K on a Na-X zeolite sample pretreated at about 623 K in vacuo. This figme clearly indicates how the choice of a polar or non-polar probe molecule results in different interactions and thus different heats. 

---