Conduction in zeolite

Sancho T, Soler J, Pina MP. Conductivity in zeolite-polymer composite membranes for PEMFCs. J Power Sources 2007 169 92-97. 

Unfortunately HU As is the only proton-conducting hydrate for which available oxygen diffusion coefficient data allow direct verification of the vehicle mechanism. For other compounds there is just an indication that this may be the mechanism. These are e.g. diffusion bottleneck considerations for ionic conduction in zeolites or the exceptionally high temperature factors for the water oxygen in and some heteropoly-... 

Fig. 4. Activation energies for cation conduction in zeolite [Breck ( 4)].

Numerical values for solid diffusivities D,j in adsorbents are sparse and disperse. Moreover, they may be strongly dependent on the adsorbed phase concentration of solute. Hence, locally conducted experiments and interpretation must be used to a great extent. Summaries of available data for surface diffusivities in activated carbon and other adsorbent materials and for micropore diffusivities in zeolites are given in Ruthven, Yang, Suzuki, and Karger and Ruthven (gen. refs.). 

Zeolite-bentonite hybrid catalysts have been prepared from ZSM-5 and Beta zeolites supplied by Zeolyst International and bentonite. The zeolite to bentonite ratio was 35/65. The Si02 to A1203 ratio of ZSM-5 and Beta was 23 and 25, respectively. The preparation of the material was conducted in the following way. The zeolite and the bentonite were bound together through mixing in a 6 1 aqueous solution at 60°C for 2h,... 

The majority of intrazeolite photooxygenations have been conducted in NaY,84 85 however, one study in the pentasil zeolite ZSM-5 demonstrates that steric confinement effects can play important roles.84 A comparison of the reactions of a series of tri-substituted alkenes in isooctane, NaY, and in ZSM-5 is given in Fig. 21. The reactions... 

The aluminosilicate versions of SSZ-31 and NCL-1 have been prepared with Si/Al ratios from 20 to The borosilicate was most conveniently prepared by using zeolite boron Beta as the source of boron. Recently, it was shown that a sodium borate source could be used with boron Beta seeds if the crystallization was conducted in sealed quartz tubes (39). In related work, a high silica Beta was converted... 

In the 1970s more-active zeolite catalysts were developed so that the cracking reaction could be conducted in the transport riser. Recently, heavier crude feedstocks have resulted in higher coke production in the cracker. The extra coke causes higher temperatures in the regenerator than are desired. This has resulted in the addition of catalyst cooling to the regeneration step, as shown in Fig. 17-25. 

Catalyst Preparation. For most of the experiments conducted in this study, nickel or vanadium impregnated non-zeolitic particles were blended with metals-free high activity cracking component. This allowed us to examine the effects of the metals on the non-zeolitic component. The high activity zeolitic particles were prepared by in-situ zeolite synthesis on kaolin-based microspheres... 

The role of zeolites as solid electrolytes is linked to water adsorption in the zeolite secondary porosity (see Section 8.2.7), which can be evidenced in the use of natural or synthetic zeolites as solid electrolytes, since the cationic conduction of zeolites is highly enhanced by the adsorption of water in the secondary porosity [112],... 

This instrument has allowed several studies that provide information not obtainable by other means to be conducted. Four examples are presented as follows The first example concerns the question of the mechanism of emission of potassium ions from potassium zeolite [7]. Earlier studies had made the assumption that this was an S-L type of ion formation mechanism [8], implying that there was a neutral potassium atom flux accompanying the flux of atomic potassium cations. Experiments performed on this instrument clearly showed that this is not the case there was no detectable neutral atomic potassium flux accompanying the cation flux. Thus this instrument was used to answer a long-standing question with an experiment conducted in one afternoon and allowed the conclusion to be reached that the mechanism is potassium ions in the solid state subliming into the gas phase. 

The data for the ion exchange isotherms were obtained from batch experiments conducted in a constant temperature agitated system utilizing tightly sealed polypropylene bottles. Conventional chemical analyses were used to obtain the cation distribution data in both zeolite and exchange solution phases. Most of the exchanges were carried out at ambient temperature for 24-72 hours. Preliminary tests had shown that equilibrium was essentially reached within a few hours. 

---