Zeolites as functionalization

Figure 2. Differential molar heats of chemisorption of ammonia at 423 K on MFI zeolites as function of the amount adsorbed Al-Sil, Fe-Sil, In-Sil, a silicalite/a.

Figure 5.22 RON value and composition of the gasoline fraction produced in the catalytic conversion of a PE pyrolysis oil over REY zeolite, as functions of the temperature.46...

Figure 8. Formation of COS on NaA and NaCaA zeolites as function of time.

The MSI Cerius2 3.8 software package was used to study physical sorption of N2 and O2 on LiLSX zeolite as function of pressure of the sorbing species. Calculations are based on the application of a Monte Carlo simulation algorithm in the Grand Canonical Ensemble [58,59]. The interaction-potential parameters used in the forcefield expression of this investigation are published in [60], together with details of the simulation setup. 

Figure 8 (a) Heat of adsorption (Q) of n-alkanes in zeolites as a function of carbon number (lines of best fit are drawn through data), (b) Heat of adsorption (Q) of n-alkanes in zeolites as function of mean pore diameter (a spline has been fitted to the data as a guide to the eye)... 

These results being quite untypical for zeolites give rise to a number of fundamental questions i) what makes the zeolite to function as an active catalyst ii) what makes N2O to function as a selective oxidant iii) what is the reaction mechanism. We shall shortly discuss the situation with these issues because of their importance for our further consideration. 

The acidic character of 5A zeolite as a function of the calcium content has been explored by different techniques propylene adsorption experiments, ammonia thermodesorption followed by microgravimetry and FTIR spectroscopy. Propylene is chemisorbed and slowly transformed in carbonaceous compounds (coke) which remain trapped inside the zeolite pores. The coke quantities increase with the Ca2+ content. Olefin transformation results from an oligomerization catalytic process involving acidic adsorption sites. Ammonia thermodesorption studies as well as FTIR experiments have revealed the presence of acidic sites able to protonate NH3 molecules. This site number is also correlated to the Ca2+ ion content. As it has been observed for FAU zeolite exchanged with di- or trivalent metal cations, these sites are probably CaOH+ species whose vas(OH) mode have a spectral signature around 3567 cm"1. 

Figure 2. (A) v(OH) ( ) and the v(=CH) ( ) wavenumbers of MBOH adsorbed on zeolites as a function of Sanderson electronegativity (B) Intensity of v(OH) band created by dissociated H2S as a function of Sanderson electronegativity...

Role of alkali and NH cations in the crystallization of ZSM-5 Introduced in an aqueous (alumino) silicate gel (sol), the bare alkali cations will behave in various ways firstly, they will interact with water dipoles and increase the (super) saturation of the sol. Secondly, once hydrated, they will interact with the aluminosilicate anions with, as a result, the precipitation of the so formed gel (salting-out effect). Thirdly, if sufficiently small, they also can order the structural subunits precursors to nucleation species of various zeolites (template function-fulfilled by hydrated Na+ in the case of ZSM-5 (11,48)). ... 

Contrary to the commodity chemical business, the key to win in the specialty products market does not lie in squeezing out profits by means of economies of scale or process optimization. Rather, it lies in the ability for fast new product launches in order to capture the largest market share as soon as possible. Since superior product quality and performance is what really differentiates one specialty product from another, the product properties need to be adjusted as required by business needs. For example, the ability to manipulate functional chemicals in detergent products such as enzymes and zeolites, as well as backbone chemicals like surfactants, is often the key to success for both the detergent manufacturers and chemical suppliers [3], This trend has created an urgent need for an efficient and effective product and process development for these products. 

Among the new application areas that could become large volume applications are the use of molecular sieves as functional powders, in odor removal, as plastic additives and in composites. The use of zeolites in solid-state applications is highly speculative. If ever practically realized that application would most probably represent a relatively small volume of the total zeolite consumption. 

Infrared spectroscopy has proven to be a very informative and powerful technique for the characterization of zeolitic materials. Most infrared spectrometers measure the absorption of radiation in the mid-infrared region of the electromagnetic spectrum (4000-400 cm or 2.5-25 xm). In this region of the spectrum, absorption is due to various vibrational modes in the sample. Analysis of these vibrational absorption bands provides information about the chemical species present. This includes information about the structure of the zeolite as well as other functional... 

At a given temperature adsorption isotherms measure the number of adsorbed molecules as a function of pressure for the fluid that is in contact with the zeolite. The simplest form is the Langmuir isotherm which treats the zeolite as a collection of equivalent adsorption sites in the absence of adsorbate-adsorbate... 

The use of zeolites can overcome many of these limitations and provide new controlled entries into these oxidized hydrocarbons and new materials. For example, some of the most valuable industrial intermediates are terminally oxidized hydrocarbons, snch as n-hexanol or adipic acid, that are not readily available in free-radical chain processes. The ability of zeolites to function as shape-selective catalysts can, in principle, be used to restrict access, by reactant or transition state selectivity, to sites not normally attacked by oxidants [3]. 

The synthesis was repeated in 1984 [136], and, because of the stability of phthalocyanines and their catalytic utiHty, these materials have continued to attract attention. Metal phthalocyanines have been used to catalyze selective oxidations under mild conditions, and have been studied as functional models of enzymes. Their formation from dicyanobenzene within a zeolite involves the condensation of the ligand precursors and the supply of two reducing equivalents, which are frequently suggested to be provided by intrazeoHtic water ... 

Figure 33a. Alkali zeolites as a function of their compositions in Al-Si-(Na,K)2 coordinates assuming Na-K end-members. Nat = natrolite Anal = analcite Ph = phillipsite Er = erionite F = feldspar S = stilbite ...

Figure 33b. Calcic zeolites as a function of their compositions in Al-Si-Cax coordinates assuming Calcium end members. F = feldspar G = gismon-dine La = lawsonite Sc = scolectite Ph = phillipsite Ch = chabazite ...

Cince the catalytic activity of synthetic zeolites was first revealed (1, 2), catalytic properties of zeolites have received increasing attention. The role of zeolites as catalysts, together with their catalytic polyfunctionality, results from specific properties of the individual catalytic reaction and of the individual zeolite. These circumstances as well as the different experimental conditions under which they have been studied make it difficult to generalize on the experimental data from zeolite catalysis. As new data have accumulated, new theories about the nature of the catalytic activity of zeolites have evolved (8-9). The most common theories correlate zeolite catalytic activity with their proton-donating and electron-deficient functions. As proton-donating sites or Bronsted acid sites one considers hydroxyl groups of decationized zeolites these are formed by direct substitution of part of the cations for protons on decomposition of NH4+ cations or as a result of hydrolysis after substitution of alkali cations for rare earth cations. As electron-deficient sites or Lewis acid sites one considers usually three-coordinated aluminum atoms, formed as a result of dehydroxylation of H-zeolites by calcination (8,10-13). 

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. 

Figure 1. Thermal stability (°C) of cation-exchanged zeolites as a function of the degree of exchange (a) (a,b) and modul (c)...

Curves of isosteric heats as functions of amount sorbed were obtained for Ar and Xe in Ba-, Na-, and K-enriched forms of zeolite L, for Kr in H-enriched forms of zeolite L, or erionite, and offretite, and for Kr in H-, Li-, Na-, K-, Cs-, Ba-, and La-enriched forms of L. Some results are shown in Figures 6a, b, and c, respectively. The abcissae give the amounts sorbed, rj, in cm3 at STP per cm3 of intracrystalline free volume, using the micropore volumes W0 of Table III to evaluate rj. This scale provides satisfactory means of comparing the sorbents. 

Feolite catalysts modified by transition metals are interesting and difficult subjects to study. In one of the first studies of zeolites as catalysts, Rabo and co-workers (1) used a zeolite catalyst containing 0.5% platinum for isomerization of n-paraffins. In this reaction the metal-zeolite system acted as a typical representative of the bifunctional catalysts. Studies of zeolites modified by transition metals ( 2, 3, Jf) showed that their polyfunctional properties are determined by the structural and chemical properties of the zeolite and by the state of the metal in it. In this paper we discuss new data on the metal state after reduction as well as the catalytic functions of zeolite catalysts containing nickel and platinum. 

Figure 1. Radical-forming activity of 90% exchanged Y zeolite as a function of activation temperature with TNB ( ) and perylene (O) as adsorbates...

The application of zeolitic materials cls catalysts in paraffin isomerization is discussed. Particular attention is given to catalyst preparation variables such as sodium removal for zeolite Y and mordenite. Dual function catalysts based on these zeolites are compared with respect to activity. A reaction mechanism for paraffin isomerization over zeolitic dual function catalysts, on the basis of literature and own data, is presented. 

Figure 3a is a schematic of the functionalized zeolite beta. Figure 3b plotted the catalytic conversion of HEX and PYC over 6 A zeolites as a function of time. For sulfonated zeolite (Z-S03H), more than 60 % HEX was converted in 4 hours, and nearly complete conversion was observed over 12 hours. On the other hand, PYC, which has a large molecular size and cannot enter the microporosity, showed less than 8 % conversion over extended reaction time with same Z-S03H as catalyst. Both HEX and PYC were also reacted over pure zeolite beta (Z), and the TMMPS functionalized zeolite (Z-SH) before it was treated with H202. Pure zeolite and Z-SH showed low catalytic activity, and only a small fraction of either HEX or PYC was converted. Further evidence of the size selectivity is provided when amines of different sizes are used to poison (neutralize) the acid sites (19). As shown in Figure 3c, the... 

Figure 4. The percent Cu(II) exchange of (0, O) Na Y, fl, Q) NHt y—89% exchanged, and (A) NHt Y—75% exchanged zeolites as a function of the final solution pH, which was altered by varying v/m from 20 cm /g (filled symbols) to 200 cm /g (open symbols) and by varying the Cu(II) solution concentration.

Metallo-phthallocyanine (MePc) complexes are known as mild oxygenation catalysts for alkanes and alkenes and as functional models for enzymes, more in particular for monooxygenases like Cytochrome P450.[44] Among the many possible supports for such complexes, zeolite FAU topologies1451 are excellent materials for their encapsulation. [46 50] The low solubility of Me Pc complexes in general and their tendency to form adducts even in solution, giving rise to self-oxidation and subsequent self-destruction phenomena, make them the ideal candidates for their distribution as individual species on a solid support. 

Fig. 1. Model of rhodium dicarbonyl complex on dealuminated Y zeolite, as determined by IR and EXAFS spectroscopies and density functional theory. The Rh atom, near the upper center of the figure, has two CO ligands bonded to it, pointing upward, and two oxygen atoms of the zeolite lattice below. An Al atom is located between these two oxygen atoms. The dangling atoms of the cluster model of the zeolite are capped by hydrogen atoms for the calculation (Goellner, Gates, etal., 2000).

In this work, the triflic acid modified Y-zeolite catalyst has been investigated for the atmospheric synthesis of MTBE and ETBE. In particular, the apparent activation energy for MTBE was determined, and this value is compared with those reported in the literature [1,6]. In addition, for both syntheses, the product selectivities are reported as functions of the contact time at the temperature where the catalyst activity is the highest. The catalyst stability for the MTBE synthesis was also examined. 

Heterogeneous catalysts are solid materials that sometimes consist of the bulk material itself, for example, acid zeolite catalysts [10] or fused catalysts [11], Or in other cases of an active component or components deposited, as a rule, on a highly developed area support, for example, silica, alumina, carbon or in some cases a zeolite. The function of the support is to enhance the catalyst properties, for example, the stability of the active component or components, or in some cases to be even included in the catalytic reaction, for example, by providing acidic sites in bifunctional zeolite catalysts [10],... 

The variations of acidic properties in the surface layers and in the bulk solid catalysts after calcination, reduction, or coking were examined by pyridine Nls XPS [4,7] and by the pyridine infrared adsorption techniques, respectively. This provides a means to compare the changes in the characteristic BrBnsted and Lewis acidity functions after those treatment conditions. First of all, TPD of ammonia revealed that both coked and regenerated samples exhibited much decreased acidity as compared with either calcined or reduced samples before the reaction of n-heptane conversion in either N2 or H2 stream [7]. The adsorption of pyridine may cause further perturbation to the Pt4+ or Pt 2+ species in the zeolite as indicated by the increase in binding energies of Pt3d5/2 electrons, as shown in Table 3 and Figure 4,... 

Extensive manifestations of configurational diffusion can be seen in catalytic zeolites. The landmark measurements by Gorring [16] of the diffusion coefficients of alkanes (in potassium T zeolites) as a function of their carbon number are shown in Fig. 4, indicating over two orders of magnitude of change in diffusivity, with a minimum at C-8 and a maximum at C-12 for unexplained reasons. Similarly, spectacular effects for more complex molecules have been observed by Haag and Chen [17] and are shown in Fig. 5. Although we do not yet have a workable correlation between zeo-... 

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