Modified zeolites

Szostak R 1991 Modified zeolites Stud. Surf. Sol. Catal. 58 153-99... 

Bio-oil upgrading over Ga modified zeolites in a bubbling fluidized bed reactor... 

Desilicated samples were obtained by alkaline treatment of calcined H-MCM-22 (Si/Al = 15). For this purpose the zeolite was suspended in 0.05-0.50 M NaOH solutions for 45 min at 323 K, followed by filtering and washing and an additional ion-exchange step to regain the H-form of the modified zeolite. 

The gallium modified zeolites were activated by two successive reduction-oxidation cycles, respectively with hydrogen and air, which, according to the literature [3], lead the catalyst to its most active form. 

We are studying the glycerol transformation in the presence of different catalysts of porous structure such as layered double hydroxides (hydrotalcites, HT and mixed oxides, MO), modified zeolites (ZSM5) and new type of Raney-Ni (RNi) to find optimal conditions for producing valuable components. 

D. Rolison, Zeolite-modified electrodes and electrode-modified zeolites. Chem. Rev. 90, 867—878 (1990). 

B.H. Liu, F. Yan, J.L. Kong, and J.Q. Deng, A reagentless amperometric biosensor based on the coimmobilization of horseradish peroxidase and methylene green in a modified zeolite matrix. Anal. Chim. Acta 386, 31-39 (1999). 

Joy, A., Robbins, R.J., Pitchumani, K. and Ramamurthy, V. (1997). Asymmetrically modified zeolite as a medium for enantioselective photoreactions reactions from sping forbidden excited states. Tetrahedron Lett. 38, 8825-8828... 

Kubica et al45 also investigated the effect of platinum-modified zeolites on the decalin reaction. They found that the addition of Pt enhances the catalyst activity. The initial isomerization was increased 3 times, which can be interpreted in terms of a change in the reaction initiation. In addition to initiation by a PC step over Bronsted acid sites, as proposed for H-form zeolites, a bifunctional initiation path... 

By batch description trials Organo- and inorganically- modified zealot was subjected up to 24 hr in distilled water, tap water and 2% Nalco aqueous solutions in laboratory shaken machine to demonstrate how strongly the examined oxyanions are bound on the modified zeolite. While only slightly chromate desorption in the maximum extent about 20 mg/L was observed, approximately one order higher arsenate desorption was found, corresponding to increased ionic strength in waters. However, in both cases ODA-clinoptilolite exhibited the lowest desorption characteristics. Here, the... 

Figure 1.32. True color fluorescence microscopy pictures of Py+ loaded and Ox+ modified zeolite L crystals of 2400-nm length, after excitation of only Py+ at 470-490 nm. (See insert for color representation.)...

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.

This section describes catalytic systems made by a heterogeneous catalyst (e.g., a supported metal, dispersed metals, immobilized organometaUic complexes, supported acid-base catalysts, modified zeolites) that is immobilized in a hydrophilic or ionic liquid catalyst-philic phase, and in the presence of a second liquid phase—immiscible in the first phase—made, for example, by an organic solvent. The rationale for this multiphasic system is usually ease in product separation, since it can be removed with the organic phase, and ease in catalyst recovery and reuse because the latter remains immobilized in the catalyst-philic phase, it can be filtered away, and it does not contaminate the product. These systems often show improved rates as well as selectivities, along with catalyst stabilization. 

Another way to modify zeolite properties is to change the nature of the nonframework cations. Some examples of how cation exchange can affect properties are noted in Section 2.6. For catalytic applications it is often desirable to create active acidic sites. This can be done by exchanging the cations with NHJ and then calcining the zeolite, removing NH3 and leaving behind protons attached to framework oxygen atoms. 

Allen, P.T. and Drinkard, B.M. (1972) Separation of mixtures with modified zeolites. US Patent 3,698,157. 

Zeolite/polymer mixed-matrix membranes prepared from crosslinked polymers and surface-modified zeolite particles offered both outstanding separation properties and swelling resistance for some gas and vapor separations such as purification of natural gas. Hillock and coworkers reported that crosslinked mixed-matrix membranes prepared from modified SSZ-13 zeolite and 1,3-propane diol crosslinked polyimide (6FDA-DAM-DABA) synthesized from 2,2 -feis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, p-dimethylaminobenzylamine-and 3,5-diaminobenzoic acid displayed high CO2/CH4 selectivities of up to 47 Barrer and CO2 permeabilities of up to 89 Barrer under mixed gas testing conditions [71]. Additionally, these crosslinked mixed-matrix membranes were resistant to CO2 plasticization up to 450 psia (3100kPa). 

Hathaway, P.E. and Davis, M.E. (1989) Base catalysis by alkali modified zeolite. f Catal, 119, 497-507. 

Uu, H.-C. (1985) Modified zeolite catalyst composition and process for alkylating toluene with methanol to form styrene. U.S. Patent 4, 499,318. 

Kawai, T Tsutsumi, K. Adsorption characteristic of surfactants and phenol on modified zeolites from their aqueous solutions. Colloid Polymeric Science, 1995 273, 787-792. 

To prepare alkali- or alkaline earth-modified zeolites or mesoporous moleeular sieves, identieal general methodologies are used. Thus, alkaline earth eation-exehanged zeolites are prepared by exehange of the zeolite in the sodium form in aqueous solution of alkaline earth metal salts, followed by washing and ealeination. Alkaline earth metal oxides loaded in zeolites are also prepared by impregnation of alkaline earth metal salts sueh as nitrates, aeetates, or ethoxides followed by ealeination (70,215,216). 

A. Catalytic Activities of Alkaline Earth-Modified Zeolites... 

Because BaO/NaX zeolite catalysts exhibited the best performance, further investigations have been carried out recently to characterize the oxidative methylation of toluene catalyzed by BaO-modified X- and Y-zeolites, mordenite, ZSM-5, sil-icalite, and ALPO4-5 (230). The authors found that activity and basicity of BaO-modified zeolites and zeolite-like catalysts depend on both the structural type and composition. Thus, for samples of the same structural type (BaO/NaX zeolite. 

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