Loading zeolite

In a recent paper Pijpers et al. [2.42] have reviewed the application of XPS in the field of catalysis and polymers. Other recent applications of XPS to catalytic problems deal with the selective catalytic reduction of using Pt- and Co-loaded zeolites. Although the Al 2p line (Al from zeolite) and Pt 4/ line interfere strongly, the two oxidation states Pt and Pt " can be distinguished after careful curve-fitting [2.43]. 

The process which was developed hy DOW involves cyclodimerization of hutadiene over a proprietary copper-loaded zeolite catalyst at moderate temperature and pressure (100°C and 250 psig). To increase the yield, the cyclodimerization step takes place in a liquid phase process over the catalyst. Selectivity for vinylcyclohexene (VCH) was over 99%. In the second step VCH is oxidized with oxygen over a proprietary oxide catalyst in presence of steam. Conversion over 90% and selectivity to styrene of 92% could he achieved. ... 

Silver(I)-loaded zeolites and silica-alumina can be used in carbohydrate coupling. The Ag(I) activates the 1-Br-substituent in this nucleophilic substitution. Because of the size of the reactants only the outer surface of the zeolites is active. 

It is well known that Rh(I) complexes can catalyze the carbonylation of methanol. A heterogenized catalyst was prepared by ion exchange of zeolite X or Y with Rh cations.126 The same catalytic cycle takes place in zeolites and in solution because the activation energy is nearly the same. The specific activity in zeolites, however, is less by an order of magnitude, suggesting that the Rh sites in the zeolite are not uniformly accessible. The oxidation of camphene was performed over zeolites exchanged with different metals (Mn, Co, Cu, Ni, and Zn).127 Cu-loaded zeolites have attracted considerable attention because of their unique properties applied in catalytic redox reactions.128-130 Four different Cu sites with defined coordinations have been found.131 It was found that the zeolitic media affects strongly the catalytic activity of the Cd2+ ion sites in Cd zeolites used to catalyze the hydration of acetylene.132... 

Compound 14 is diamagnetic and represents the first tetrasodium-dication cluster that is stabilized by two sterically congested silyKflu-orosilyl)phosphanide counterions (see Section II,D). It has been also independently synthesized through sodium consumption of 13 in the presence of styrene as catalyst in 24% yield. The electron reservoir of the Na) cluster can serve for reduction processes, that is, it reduces Me3SiCl to hexamethyldisilane (see Section II,F). The fact that 14 is intensely yellow, and not red or blue as observed for Na-loaded zeolites (28), suggests that the residual metal electrons are probably much less delocalized. 

Fig. 13. Uniform bifunctional platinum-loaded zeolite catalyst. Large white dots (Pt) are 0.5 nm in diameter.

It has been reported (Calzaferri et al., 1984) that oxygen from water is evolved upon irradiation of a silver-loaded zeolite (a group of alumino-silicates) suspension according to the following overall stoichiometry ... 

Figure 1.13. (1) Electron microscopy picture of a zeolite L crystal with a length of 1.5 pm. (2-5) True color fluorescence microscopy pictures of dye loaded zeolite L crystals. (2-4) Fluorescence after excitation of only Py+ (2) after 5-min exchange with Py+, (3) after 2 h exchange with Py+, (4) after additional 2 h exchange with Ox+. (5) The same as 4 but after specific excitation of only Ox+. (See insert for color representation.)...

Important transfer and transformation processes of electronic excitation energy that can take place in dye loaded zeolite materials are... 

It is a challenge to couple the antenna systems to a device (e.g., a semiconductor). It has already been shown that it is possible to prepare organized zeolite monolayers on flat surfaces [78, 79]. For coupling, the interface between the chromophore loaded zeolite L antenna systems and the semiconductor becomes very important. Stopcock molecules are expected to function as a bridge between the chromophores in the zeolite L channels and the device surface, which will open a whole new exciting research area. The first successful experiments with slopcock modified crystals have been reported recently [80]. 

A continuous process based on hydrodynamic cavitation can be employed to prepare a wide variety of metal oxides in grain sizes of 1 -10 nm, such as iron oxide, bismuth molybdate, perovskites, platinum-loaded zeolite, and other ceramics and superconductors [170]. The method uses a microfluidiser for mechanically generating hydrodynamic cavitation and the internal pressure of the liquid media is elevated from ambient pressure to between 1000 to 25 000 psi. 

Infrared spectroscopy can be used to obtain a great deal of information about zeolitic materials. As mentioned earlier, analysis of the resulting absorbance bands can be used to get information about the structure of the zeolite and other functional groups present due to the synthesis and subsequent treatments. In addition, infrared spectroscopy can be combined with adsorption of weak acid and base probe molecules to obtain information about the acidity and basicity of the material. Other probe molecules such as carbon monoxide and nitric oxide can be used to get information about the oxidation state, dispersion and location of metals on metal-loaded zeolites. 

Figure 4.40 P MAS NMR chemical shift ranges for Bronsted and Lewis acid sites in trimethyl phosphine (IMP) loaded zeolites.

Isomerization of olefins or paraffins is an acid-catalyzed reaction that can be carried out with any number of strong acids, including mineral acids, sulfated metal oxides, zeolites and precious metal-modified catalysts [10]. Often the catalyst contains both an acid function and a metal function. The two most prevalent catalysts are Pt/chlorided AI2O3 and Pt-loaded zeolites. The power of zeoHtes in this reaction type is due to their shape selectivity [11] and decreased sensitivity to water or other oxygenates versus AICI3. It is possible to control the selectivity of the reaction to the desired product by using a zeoHte with the proper characteristics [12]. These reactions are covered in more detail in Chapter 14. 

Armor, J. N. NO /hydrocarbon reactions over gallium loaded zeolites A review, Catal. Today, 1996, Volume 31, Issues 3-4, 191-198. 

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/... 

Figure 6 Occupation probability p of the -loaded zeolite L at room temperature as a function of Cmv2+. which is the number of moles of per mole of zeolite L...

The two cationic dyes, Py+ as a donor and Ox" as an acceptor, were found to be very versatile for demonstrating photonic antenna functionalities for light harvesting, transport, and capturing, as illustrated in Fig. 7. They can be incorporated into zeolite L by means of ion exchange, where they are present as monomers because of the restricted space. In this form they have a high fluorescence quantum yield and favourable spectral properties. The insertion of the dyes can be visualised by means of fluorescence microscopy. The fluorescence anisotropy of Ox -loaded zeolite L has recently been investigated in detail by conventional and by confocal microscopy techniques [15],... 

Figure 11 Fluorescence and excitation spectra of DPH-loaded zeolite L at 100, 180, 200, 240, and 293 K (top to bottom). The fluorescence spectra have been scaled to the same height as the corresponding excitation spectra. The excitation spectra have not been normalized to the same integral in order to demonstrate the decreasing fluorescence intensity with increasing temperatures.

Figure 12 Temperature dependence of the spectral overlap of DPH-loaded zeolite L. Note that the values are 10 times smaller compared with the overlap integrals in Fig. 10.

Figure 14 (a) Excitation distribution along the channel axis of a zeolite L crystal consisting of 90 slabs (occupation probability p = 0.3) under the condition of equal excitation probability at f = 0 calculated for front-back trapping. Fluorescence of the donors is taken into account. (1) t = 5 psec, (2) f = 10 psec, (3) t = 50 psec, and (4) t = 100 psec after irradiation, (b) Predicted fluorescence decay of the donors in absence of acceptors (dotted curve), in the presence of acceptors at both ends (solid curve), and fluorescence decay of the acceptors (dashed curve), (c) Measured fluorescence decay of Py -loaded zeolite L (ppy = 0.08) (dotted curve), Py -loaded zeolite L (p y = 0.08) with, on average, one Ox acceptor at both ends of each channel (solid curveX and fluorescence decay of the Ox acceptors (dashed curve), scaled to 1 at the maximum intensity. The experiments were conducted on solid samples of a monolayer of zeolite L crystals with a length of 750 nm on a quartz plate. 

A. Fata Morgana Effects in Dye-Loaded Zeolite L Crystals... 

Optical effects due to refraction and total internal reflection have been observed in dye-loaded zeolite L crystals of 2.5 p,m length and 1.4 p-m diameter by means of an optical microscope equipped with polarizers, a narrow band, and cutoff filters [23]. An astonishing effect taking place in an Ox +-loaded crystal is seen in Fig. 15. Looking at the polarized red emission, a homogeneous intensity distri-... 

Figure 15 Polarized fluorescence microscopy images of a 2.5-p,m-long Ox +-loaded zeolite L crystal after excitation at 545-580 nm (cutoff 605 nm). The arrows indicate the transmission direction of the emission polarizer.

Figure 17 Fluorescence microscopy images of a standing 2.5-n.m-long DMPOPOP-loaded zeolite L crystal upon excitation at 330-385 nm and observed with a cutoff filter (410 nm) (a) in air and (b) in a refractive-index-matching solvent.

In Fig. 12 in Ref 25, fluorescence microscopy images of different dye-loaded zeolite L single crystals are shown. Each line consists of three pictures of the same sample, but with different polarizations of the fluorescence observed. In the first one, the total fluorescence of the crystals is shown, and in the others, the fluorescence with the polarization direction indicated by the arrows is displayed. The zeolite was loaded with the following dyes (A) Py+, (B) PyGY", (C) PyB +, (D) POPOP (see Table 1). Most crystals show a typical sandwich structure with fluorescent dyes at the crystal ends and a dark zone in the middle. This situation can be observed when the diffusion of the dyes in the channels has not yet reached its equilibrium situation. It illustrates nicely how the molecules penetrate the crystals via the two openings on each side of the one-dimensional channels. 

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