Zeolites modification after

Successful complexation of the exchanged transition metals by the tetradentate ligand salen was indicated by the typical yellow/brownish colour of the prepared inclusion compounds. X-ray powder diffraction and scanning electron microscopy reveal that the crystallinity of the zeolite host is virtually retained during the modification steps. Furthermore, no crystals of the salen ligand or of metal-salen complexes are visible on the external surface of the zeolite crystallites after careful piuification via soxhlet extraction with acetone. Analysis of the used solvent by UVATS-spectroscopy revealed that only salen but no metal-salen complexes were removed from the zeolite during extraction. This indicates that the complexes are truly entrapped in the intracrystalline voids of the zeolite. It has been demonstrated [7] that the presence of salen and PdSalen in zeolite Y can be probed by IR-spectroscopy in... 

It seems that practical implementation of this type of selective catalysts will require a medium in which (very) polar products can be removed from the zeolite phase. Unfortunately, no attention has been paid in literature to such issues. On the contrary, some attention has been devoted to host modification after exchange of NaY with other alkali metal cations [37]. The cyclohexene epoxidation activity increases with decreasing size of the charge compensating cation pointing to the influence of steric effects or of electrostatic effects on the activity. In competitive experiments using cyclohexene and 1-octene as feed, the reactivity of the smaller substrate is suppressed, indicating that competitive sorption is involved as well [37],... 

In 2001, Masuda et al. (2001) developed a catalytic cracking deposition (CCD) technique for zeolitic pore size reduction to enhance the H2 separation factor of MFI zeolite membranes. After the CCD modification, the zeolite pore size was reduced to about 0.36—0.47 nm, and the H2/CO2 separation factor of MFI zeolite membranes was enhanced from 1.5—4.5 to more than 100. However, the H2 permeance of the modified membrane was only about one-tenth of the fresh membrane. Using the method developed by Masuda et al., Falconer and co-workers modified B-ZSM-5 and SAPO-34 membranes for the enhancement of H2/CO2 separation factor (Hong, Falconer, Noble, 2005). Similarly, the H2/CO2 separation factor of the modified membrane was increased to 48, while the H2 permeance of the B-ZSM-5 membrane was decreased by more than one order of magnitude. 

After the catalytic runs no modification of mean particle size is observed for this last system. Conversly, Ru CO) deposited on silica-alumina is readily decomposed at 200°C to metallic particles of 1 nm mean size which are also catalysts for the F-T synthesis. The catalytic activity at 200°C is C i one tenth of the Y zeolite supported ones and methane is practically the only hydrocarbon formed. Electron microscopy examination of the catalyst after reaction reveals a drastic sintering of the... 

Figure 1.33. Upper electron microscopy (EM) pictures of the investigated zeolite L samples with different crystal length lz (1) 300 nm (2) 500 nm (3) 850 nm (4) 1400 nm (5) 2400 nm. Lower Fluorescence intensity after specific excitation of only Py+ at 460 nm (scaled to the same height at the maximum of the Py+ emission) of Py+ loaded and Ox+ modified zeolite L crystals with constant Py+ loading (ppy+ = 0.11) as a function of crystal length. The Ox+ modification was two molecules at both ends of the channel, on average.

In addition to the thermal and ion exchange treatments described above, another rich area in the study of zeolite stabilizahon and acidity modification involves a broad class of post stabilization chemical treatments to remove extra-framework aluminum, and silicon, species parhally or completely after steaming. In actual commercial practice, such treatments primarily involve use of mineral acids such... 

The immobilization of Ru-phthalocyanines follows routes similar to those employed for the analogous Fe complexes. Particularly, the perfluorinated Ru phthalocyanines were immobilized in zeolites by ship-in-a-bottle synthesis or by template synthesis, or in MCMs after surface modification. The materials display extremely high activities for the oxygenation of paraffins with r-BuOOH as the oxidant (128,288). 

There is an important problem related to the utilization of spent adsorbents and catalysts, especially natural zeolites, used in chemical, petrochemical and food industries after adsorbing large amounts of organic substances.5-7 As a whole they can be used as raw materials to prepare carbon-mineral adsorbents.8 Therefore, the aim of this work was to elucidate the influence of different factors such as the kind of organic precursors and inorganic matrices, including spent adsorbents, and the preparation and modification techniques on the structural and adsorption properties of carbon-mineral adsorbents. 

DSC up to 875 K without pre-adsorption of 4-methyl quinoline did not resolve significant differences between sample OW-ZSM-5 and sample lOW-ZSM-5 (Figure 3, curve a, c). The DSC curve of the unloaded zeolite shows that water desorption proceeds in several steps characterized by three endothermic processes. The process at 560 K is most likely caused by condensation of hydroxyls preceding water desorption. These three endothermic processes are retained even after modification with 12-tungstosilicic acid (sample 1 OW-ZSM-5). 

The effect of the acidity of polyfunctional zeolite catalysts on their activity in benzene alkylation by propene has been examined.Crystalline zeolites exist with a variety of characteristic pore and channel sizes. In the case of ZSM-5 zeolite, the interconnected channels formed by 10-membered rings of oxygen atoms allows certain benzene derivatives to fit rather closely, diffuse into the pores, and, after undergoing a reaction, diffuse out. This is the origin of the high para selectivity in reactions such as alkylation of toluene by methanol catalyzed by zeolites like ZSM-5 and related modifications. ... 

Deactivation for Y-REO-zeolite with different high REO concentrations was studied. The REO can be incorporated into the Y-zeolite around 12% wt and it can be followed by the cell parameter modification. For both fresh and deactivated samples, below 4% wt of REO the total acidity, and the HTI were increased but beyond this REO concentration the total acidity and the HTI decreased as the REO amount increased. The cell parameter and the total acidity diminished for all samples after the deactivation. This behavior was observed when the HTI was analyzed as a ftmction of cell parameter, REO content and total acidity. It is clear that the control of REO content in FCC catalyst is one of the most important task for high octane gasoline production. 

The concentration of acid sites was determined by temperature programmed desorption (t.p.d.) of NH3. The degree of ion exchange was calculated from the difference in concentration of the strong Brensted acid sites present before and after ion exchange. The structure of the zeolites after synthesis or postsynthetic modification was verified by XRD. 

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