Zeolite catalysts, preparation

Molybdenum/zeolite catalysts prepared by impregnating zeolites with ammonium hepiamolybdate solution generally give rise to poor dispersion of molybdenum [2]. In contrast, ion exchange would be an ideal method for loading active metal species onto supports. Few cationic forms are available as simple salts of molybdenum of high oxidation... 

As the zeolite catalyst preparation is not trivial, a catalyzed epoxidation reaction serves to demonstrate the feasibility of gas/liquid/solid processing using this industrially well-applied catalyst class [30]. 

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. 

To develope the scientific bases of zeolite catalysts preparation for selective organic and petrochemical synthesis, the elaboration of methods of directed modification of acid properties of these systems seems to be very important, namely, the creation in them of acid sites of different nature and the determination of their irole in multi-route catalytic transformations. 

Catalytic Evaluation In order to investigate support effects in these iron/zeolite catalysts prepared from Fe3(C0)12 by the extraction technique, three catalysts of similar weight percent iron loading were evaluated for their ability to catalyze synthesis gas conversion these catalysts were 15.0% Fe/ZSM-5, 16.4% Fe/Mordenite andl5.0% Fe/13X. All catalysts were evaluated under similar conditions as described in the experimental section. Catalytic data is presented in the accompanying figures in each figure the first three points for each catalyst are data obtained at 280°C, the second three points are data at 300°C. 

The adsorption of CO molecules is often used to probe surface Cu+ sites (107, 236). After evacuation of Cu(II)zeolite samples at 973 K, the EPR signal assigned to the copper(II) species become weak and can hardly be observed, indicating that the Cu " ions were reduced to Cu+ (see Section IV.D.2.a). With the Cu(l)zeolite catalysts prepared in this way, the photoluminescence was observed upon excitation at about 300 nm (Fig. 31). The... 

Catalyst Characterization. Chemical analyses, x-ray diifraction analyses, and gas adsorption procedures were used to characterize the composition, crystallographic character, and surface structure of the nickel and cobalt zeolite catalyst preparations. The chemical and x-ray procedures were standard methods with the latter described elsewhere 11). Carbon monoxide chemisorption measurements provide useful estimates of the surface covered by nickel atoms from the zeolite substrate 10). 

The Co-salophen / zeolite catalyst, prepared by template synthesis method was active in the oxidation of hydroquinone to benzoquinone (Fig. 2) and produced similar oxygen uptake curves as the free complex. It was also possible to reuse the catalyst in a subsequent run with a similar activity as in the first run. 

We have also prepared the Co-salophen/zeolite catalyst, using the template synthesis and the flexible ligand method. The Co-salophen/zeolite catalyst prepared by the template synthesis method proved to be active in the oxidation of hydroquinone and in the aerobic oxidation of 1-octene and the acetoxylation of cyclohexene. The zeolite-encapsulated catalyst was active and produced the same selectivity and yield as the free complex. It was also possible to remove the catalyst and to reuse it in subsequent experiments. 

Sulfur tolerances of Cu- and H-mordenite zeolite catalysts prepared by ion-exchange were examined in a fixed-bed flow-reactor system. Rates of reduction of NO over HM or CuHM with C2H4 and CuNZA with C3H6 are decreased by SO2 included in the feed gas stream. Surface areas and sulfur contents of the deactivated catalysts, their TGA and TPSR patterns and observations by XPS and Raman suggest the formation of a sulfur species on the catalyst surface in the form of sulfate (SO/ ) which causes the loss of NO removal activity of the catalysts. Data from Cu K-edge absorption spectra suggest sulfur electrostatically interacts with Cu ions on the catalyst surface. 

Bai et al. [330] found a remarkable selectivity (88% in the steady-state reaction and 94% in the pulse reaction) in the direct synthesis of phenol from benzene with molecular oxygen over a Re/zeolite catalyst prepared by chemical vapor deposition (Figure 3.62). However, stable performances could be obtained only by continuous feeding of relatively high concentrations of NH3 (around 30%), which is necessary to stabilize the active complex containing interstitial N atoms (see the model of the complex in... 

Ni/H)3 zeolite catalysts prepared by the deposition-precipitation method R. Nares, J. Ramirez, A. Guttierrez-Alejandre, R. Cuevas, C. Louis and... 

The mimic is prepared by sequential ion-exchanges with iron(ll) and Pd(ll) tetrammine cations followed by calcinations and reduction of the Pd(ll) to Pd(0) as previously described(14). A material with 2wt% Fe(ll) and 1wt% Pd(0) is used by immersing the dry zeolite solid in neat substrate alkane and then pressuring the reaction vessel with a 3 1 mixture of oxygemhydrogen. After shaking this mixture at room temperature for 4 hours the products are analyzed by capillary GC. As a control to assess the intrinsic selectivity of such a Pd/Fe system in the absence of steric effects of the zeolite, catalysts prepared with amorphous silico-aluminate supports were run for comparison. In these cases all reactions must take place at the particle surface since there is no interior pore structure available. In addition, comparison of reaction selectivities of this catalysts with our zeolite materials allows us to ascertain that the Fe active sites must be actually inside (and not on the exterior surface) of the zeolite crystallites. 

COMPARISON OF HYDROSULFURIZATION ZEOLITE CATALYSTS PREPARED IN DIFFERENT WAYS... 

The performance of the catalysts was tested in N2O decomposition. This reaction is well catalyzed by Fe-zeolites, and therefore the appropriate model reaction for this type of materials. The performance was compared with two Fe-zeolite catalysts prepared through conventional ion-exchange of NH4-form zeolites. As indicated in Figure 3 (right) the performance of the one-pot catalyst was even superior to the conventionally prepared. The reason for this is ascribed to the minimisation of the FeOx formation, which takes place in the classical preparation (TPR profiles not shown). 

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