Solid state ion exchange

Zeolite-supported Co catalyst was synthesized by solid-state ion exchange using the procedure described by Kucherov and Slinkin[16, 17], CoO... 

Solid-state ion exchange dynamics of cadmium in zeolite Y... 

Keywords solid-state ion exchange, high-temperature X-ray diffraction, zeolite Cd-Y. 

Fig. 5 shows the time dependence of the solid-state ion exchange process. The process has pseudo first order kinetics in the investigated conversion range for both (i) the distribution and crystallinity loss of the CdCl2 salt and (ii) the formation of new Cd,H-Y phase. The rate constant obtained for the decay of... 

The high temperature XRPD technique can be used to investigate the dynamics of solid-state ion exchange of zeolites. Data suggest that the rate of Cd2+ ion transport in the zeolite Y micropores controls the rate of the solid-state ion exchange. 

Selective catalytic reduction of NOx by NH3 on V-Mo-zeolite prepared by solid-state ion exchange method... 

V-Mo-Zeolite catalysts prepared by solid-state ion exchange were studied in the selective catalytic reduction of NOx by ammonia. The catalysts were characterized by chemical analysis, X-ray powder diffraction, N2 adsorption (BET), DRIFT, UV-Vis and Raman, spectroscopy and H2 TPR. Catalytic results show that upon addition of Mo to V-ZSM-5, catalytic performance was enhanced compared to V-ZSM-5. 

H2 TPR measurements are used to probe the reducibility and may reveal more information on the nature of vanadium and molybdenum species. The assignment of the TPR peaks has been based on the literature study [9, 10] but also by using two reference samples V1-Z15 and Mol-Z15 prepared by solid-state ion exchange. TPR thermograms of V-Mo-Zeolite systems can be divided into two zones of H2 consumption (/) Mo-Zeolites exhibit two reduction peaks at 600 and 850°C corresponding to the reduction of Mo6+ into Mo4+ through the Mo5+ step and to the reduction of Mo4+ into Mo°, respectively while (ii) V-Zeolites led to a broad asymmetric feature around 710°C, which has been previously attributed to the reduction of V5+ into V3+. Finally, the TPR profiles of V-Mo-Zeolite catalysts seem more like a superposition of both Mo and V-catalysts TPR profiles. 

The catalyst samples were prepared in our laboratory. The synthesized Na-ZSM-5 zeolite was modified by conventional or solid state ion-exchange [11] to form H-, Fe-, Cu-, Ni- and Ti-ZSM5 samples, while the mesoporous catalysts (Fe- and Ti-MCM-41) were synthesized by isomorphous substitution [12], as well as the hydrotalcites containing Fe-, Cu-, Cr- or Ca-oxide in the Mg,Al-LDH structure [13]. 

The dispersion and solid-state ion exchange of ZnCl2 on to the surface of NaY zeolite by use of microwave irradiation [17] and modification of the surface of active carbon as catalyst support by means of microwave induced treatment have also been reported [18]. The ion-exchange reactions of both cationic (montmorillonites) and anionic clays (layered double hydroxides) were greatly accelerated under conditions of microwave heating compared with other techniques currently available [19.]... 

The solid-state ion-exchange reactions, which do not have such limitations, are proving to be an interesting, practical, and low-energy alternative to the preparation of clay catalysts. 

Another example is the synthesis of supported oxide catalysts by spreading of one oxide across the surface of another (support) oxide in physical mixtures. Also, the phenomenon of solid-state ion exchange in zeolites may be discussed within the framework of the wetting and spreading concept. 

Figure 9 NOx reduction efficiency of overexchanged Fe-MFI catalysts prepared by using ( ) a conventional ion exchange in an aqueous slurry(9,0,M) ci sublimation technique and (A,A) a solid-state ion exchange. The feed gas composition for (A,9,0,M) was NO, 2,000 ppm i-C4Hio, 2,000 ppm O2, 3% H2O 0 or 10% GHSV = 42,000 k, and that composition for (A, A) was NO, 1,000 ppm i-C Hu), 1,000 ppm O2,3% H2O 0 or 0.7% GHSV = 30,000 k. (Closed symbols) in the dry feed stream (open symbols) in the wet feed stream (adopted from refs. 55,136 and 139)...

Figure 14 NO removal activity of Co-MFI catalysts prepared by different methods (9,0) chemical vapor deposition, Co-MFI-226 ) solid-state ion exchange, Co-MF 1-196 and wet ion exchange, Co-MFI-88. Reaction...

It is of relevance that very little isotope exchange is detected, in Fig. 20, for a physical mixture of HY with a neutralized Pd/NaY. As the physical mixture was rereduced after mixing, some solid-state ion exchange between Pd/NaY and HY will have taken place the Pd-proton adducts formed in this stage will account for the observed low rate of exchange. 

Figure 8. Far-infrared spectra of zeolites prepared by solid state ion exchange. Reproduced with permission from reference 28.

The far infrared experiments also showed that the effectiveness of solid state ion exchange depends on the starting form of the zeolite. NH4Y allows effectively complete ion exchange on reaction with metal halide salts, due to the initial formation of NH4CI. With HY, on the other hand, it is difficult to achieve exchange levels beyond 50% due to the immediate formation of HCl which dealuminates the zeolite to a considerable extent. 

INTRODUCTION OF NOBLE METALS INTO SMALL PORE ZEOLITES VIA SOLID STATE ION EXCHANGE... 

A novel method for the preparation of metal containing small pore zeolites is described. The metal is introduced at elevated temperatures by solid state ion exchange. The zeolites obtained by the new method are highly shape selective. As an example, the competitive hydrogenation of an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l) over various platinum, palladium and rhodium containing 8-membered ring zeolites was studied. 

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