Zeolite thermal behavior

In Japan, clinoptilolite is the commonest zeolite formed from altered pyroclastics. Four modes of occurrence have been found, replacement of vitric materials and precipitation in interstitial voids being predominant. By chemical analyses, clinoptilolite is classified into 3 types, Ca-, Na-, and K-type. In a ternary diagram of Ca(Mg), Na, and K, the field of clinoptilolite is not overlapped by that of heulandite. The x-ray powder profiles of clinoptilolites resemble that of heulandite, but their thermal behavior differs. When heated to 250°C, heulandite changes to heulandite-B this transition is not observed in clinoptilolite. Furthermore, the thermal behavior of Ca-clinoptilolite differs from alkali-clinoptilolite. This may be attributed to the difference of dehydration between Ca-clinoptilolite and alkali-clinoptilolite, which seems to depend on the atomic ratio of Ca and alkalies. 

Therapy, adjuvants Thermal activation, clinoptilolite Thermal analysis, ETS-4 Thermal behavior, clinoptilolite Thermal desorption Thermal stability, FAU Thermal stability, MOR Thermal stability, zeolites Thermal treatment, MFl... 

Tartaglione et al. [62] have recently studied the thermal behavior of melt-compounded PP/sepiolite composites (3 wt% loading) and the effect of the clay surface modification. In inert atmosphere, the catalytic activity of sepiolite on PP pyrolysis was confirmed, except for the begiiming of the degradation process (less than 20% of mass loss) where the presence of the clay improved the polymer stability (Figure 12.21a). This was explained by the adsorption of PP volatile products by the sepiolite external surface and internal zeolitic channels. 

Figure 17 shows a crossover between two thermal behaviors in both bulk EG and EG confined in a zeolite beta 3D network and AIPO4-5 nanotubes. When alcohol is trapped in cages with a pore diameter less than 0.6 nm, the severe confinement induces strong behavior at all T studied. Note that the relaxation times for EG in sodalite are significandy slower than those in silicalite or H-ZSM-5. The behavior of supercooled liquids is typically characterized by two relaxations ... 

Dehydration with rearrangement of extra-framework cations without considerable changes in the geometry of the framework and in the cell volume. Zeolite A, faujasite, natural chabazite, and mordenite provide examples of this thermal behavior. 

Hydrocracking, 30 48-52 behavior, thermal, 29 269 catalytic, 26 383 deethylation, 30 50 demethylation, 30 50 metallocarbene formation, 30 51-52 of f -decane, 35 332-333 primary coal liquids, 40 57 procedure, 40 66-67 product distribution, 30 49 reactions, over perovskites, 36 311 suppression by sulfur, 31 229 zeolite-supported catalysts, 39 181-188... 

Tschatifeser, P. and Parker, S.C. (1995) Thermal expansion behavior of zeolites and AIPO4S. J. Phys. Chem., 99, 10609-10615. 

A thermal oxidation of 2,3-dimethyl-2-butene, 16, occurs in NaY when the temperature of the oxygen-loaded zeolite in raised above — 20°C [35], Similar thermally initiated oxidations were not observed for the less electron rich tram-or cix-2-butene. Remarkably, pinacolone was conclusively identified as one of the products of the reaction of 16, This ketone is not a product of the photochemical Frei oxidation (vide supra) and underscores the very different character of these two reactions and the complexity of the oxygen/16 potential energy surface, A rationale for the different behavior could lie in the different electronic states of the reactive oxygen-CT complex in the thermal and photochemical reactions. Irradiation could produce an excited triplet-state CT complex ( [16 O2] ) and/ or ion pair ( [16 02 ] ) with different accessible reaction channels than those available to a vibrationally excited ground-state triplet complex ( [16 "02]) and/... 

These results indicate that dealumination by thermal treatment seems easier for zeolites with a low Si/Al ratio, in good agreement with the behavior of the acidic hydroxyl groups shown in Figure 5. 

The spectral behavior of CO bonded to metal atoms (metal carbonyls) has been used to characterize the surface of solids (61). For instance, it is known that metal carbonyl interacts with surface site of metal oxides and zeolites to form a Lewis-type adduct where a CO ligand of the metal carbonyl interacts (via the oxygen atom) with surface OH groups or with co-ordinatively unsaturated metal ions (surface Lewis acid sites) (62,63). On the other hand, thermal treatment of the metal carbonyl support adducts lead to loss of CO with formation of subcarbonyls, which are anchored to the support (64,65). Papile et al. (66) reported the characterization... 

The temperature-dependent irreversibility demonstrates that the ion-exchange behavior of NaX towards bivalent cations depends strongly upon the thermal history of the sample. The rather pronounced differences in behavior of transition-metal ions, also observed in synthetic zeolite 4 A (9) is in very sharp contrast with the nearly identical, either hydrated or crystallographic, dimensions of these ions (10). Obviously, this observation raises important questions as to the value of the current interpretation (nearly) exclusively in terms of physical dimensions of ions and pore width. In contrast, the similarity of behavior in mont-morillonite is remarkably close the AG0 value for the replacement of Na by either Ni, Co, Cu, or Zn is —175 cal ( ll)/equivalent, irrespective of the nature of the cation (11). Therefore, the understanding of their difference in behavior in zeolites must take other effects into consideration. 

Qynthetic and natural zeolites are becoming increasingly important as catalysts, carriers of catalysts, and adsorbents. Zeolites are especially suited to these purposes because their properties can be modified by cation exchange. The literature describes several studies which show characteristic changes in physicochemical properties resulting from cation exchange— e.g., catalytic activity (1,2), acidic properties (3), adsorption behavior (4), structure of solid (5,6), and thermal stability (7,8). 

Few systematic investigations of the behavior of the thermal stability of cation exchanged Y zeolites as a function of modul (Si02/Al203 mole ratio), cation type, degree of exchange, and activation conditions have been published. This work uses the results of IR and ESR spectroscopy to explain the behavior of thermal stability of modified Y zeolites. 

Recent work (l, 2, 3) by the junior author and his colleagues on thermally cycled gas compression by adsorption/desorption of N20 and other gases in zeolites created a need for a theory derived from first principles. Such a theory would be capable of accounting for the detailed physical behavior over a wide range of pressures, and thereby establish a reliable formalism to predict behavior and design apparatus. More important, however, is the need for a unifying theory to support and accelerate further work on all aspects of zeolite research and their applications. 

By comparing these results to those obtained using the vanadium porphyrin precursor, it can be concluded that vanadium from the porphyrin tends to stay on the matrix after thermal pretreatments (see Fig. 4), whereas vanadium from the naphthenate is preferentially associated with the zeolite after steaming, Fig. 9. These observations are in agreement with the report (1) that vanadium impregnated from vanadyl naphthenate migrated to the zeolite from the matrix surface during steam treatment. This different behavior of the two precursors... 

The choice among the variety of different types of zeolites and related materials in a practical situation will depend on the characteristics of the reacting system and the types of selectivity effects to be expected. The pore size, the deactivation behavior and the chemical and thermal stability of the zeolite material determine whether or not a particular catalyst is attractive. The necessary condition for shape-selectivity effects to occur is that the pore size has to meet the dimensions of the reacting molecules. The radius of the crystallites as well as the strength and the number of the acid sites may then be adapted to the actual requirements during synthesis. 

Photochemical activation (15) and thermal activation (11,16, 17) of iron carbonyl complexes In various zeolites have been reported. Part of our study Is to use Mossbauer spectroscopy to Investigate the behavior of Fe(C0)5 on several zeolites when activated photochemically and thermally. Another part of our study Is to Investigate the novel preparation method of Scherzer and Fort (18) that Introduces iron Into (in their study) zeolite NH Y as an anionic complex. Finally, we will report the preparation of ferrocene sublimed onto zeolite ZSM-5. The photochemical and thermal activation of these systems will be reported as well as preliminary results of the photochemical isomerization of olefins by Fe(C0)5 zeolites and the thermal activation of Fischer-Tropsch catalytic systems. It also should be noted here that our Mossbauer studies involve an in-situ pretreatment cell which can be heated to 500°C under various gaseous atmospheres. 

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