Zeolite base properties

Controlled removal of the template is especially important when zeolite based membranes are involved consisting of a continuous MFI layer on a ceramic or sintered metal support (ref. 14). In these novel composite ceramic membranes the formation of cracks during template removal would be detrimental. The unique properties (ref. 14) of metal-supported MFl-layer membranes prove that indeed crack formation can be essentially prevented. 

Alumina is an amphoteric catalyst, which can difficult to characterize via chemical and physic methods. The transformation of cyclopentanol/cyclohexanone mixture allows us to estimate at the same time the acid-base properties of aluminas. From this transformation, it was shown that aluminas can be classified into two families only basic aluminas, such as theta, which were more basic than MgO, and acido-basic aluminas, eta, gamma and delta, which possess an acidic character less pronounced than dealuminated HMOR zeolite... 

The present work reports the results obtained in the Friedel-Crafts acylation of different aromatic substrates catalyzed by zeolite Beta obtained according to a novel method based on the crystallization of silanized seeds, as a way to perturb the subsequent crystal growth step and to modify the zeolite textural properties [5], The catalytic behavior of this material is compared with that of the conventional Beta zeolite. 

Ethylbenzene plants, 23 330-331 Ethylbenzene-styrene complex, 23 328 Ethylbenzene synthesis molecular sieves in, 16 845 zeolite-based alkylation in, 23 331-333 Ethyl benzoate, 3 635 Ethyl P-D-glucopyranoside, 4 701 7-Ethylbicyclooxazolidine, antimicrobial used in cosmetics, 7 831t Ethyl bromide, physical properties of, 4 351t... 

In the present work ir, esr and microcalorimetry techniques were used to characterize the acid-base properties of acid ZSM-5 and ZSM-11 samples. Complementary studies by TEM, EDX-STEM and XPS were also carried out to determine the size and shape of zeolite particles and the A1 distribution within a particle. Catalytic properties for methanol conversion were also determined. 

The most commonly employed crystalline materials for liquid adsorptive separations are zeolite-based structured materials. Depending on the specific components and their structural framework, crystalline materials can be zeoUtes (silica, alumina), silicalite (silica) or AlPO-based molecular sieves (alumina, phosphoms oxide). Faujasites (X, Y) and other zeolites (A, ZSM-5, beta, mordenite, etc.) are the most popular materials. This is due to their narrow pore size distribution and the ability to tune or adjust their physicochemical properties, particularly their acidic-basic properties, by the ion exchange of cations, changing the Si02/Al203 ratio and varying the water content. These techniques are described and discussed in Chapter 2. By adjusting the properties almost an infinite number of zeolite materials and desorbent combinations can be studied. 

There are, however, two limitations associated with preparation and application of zeolite based catalysts. First, hydrothermal syntheses Umit the extent to which zeolites can be tailored with respect to intended appUcation. Many recipes involving metals that are interesting in terms of catalysis lead to disruption of the balance needed for template-directed pore formation rather than phase separation that produces macroscopic domains of zeoUte and metal oxide without incorporating the metal into the zeohte. When this happens, the benefits of catalysis in confined chambers are lost. Second, hydrothermal synthesis of zeoHtic, silicate based soHds is also currently Hmited to microporous materials. While the wonderfully useful molecular sieving abihty is derived precisely from this property, it also Hmits the sizes of substrates that can access catalyst sites as weU as mass transfer rates of substrates and products to and from internal active sites. 

Recently, a combinatorial investigation of alkylation of toluene with methanol to produce styrene with basic zeolites and alkaline earth catalysts was performed (257). The results of tests involving preparation and testing of more than 200 catalysts were modest, and these results emphasize that fine-tuning of the acid and base properties necessary to achieve better alkylation catalysts is not an easy task. 

It is well known that the elements in framework of zeolite molecular sieves greatly influence the properties and behaviors of these materials [1-3], The introduction of heteroatoms into the framework has become one of most active fields in study of zeolites. The investigations were mostly focused on the methods to introduce heteroatoms into the framework (for examples, hydrothermal synthesis and post-synthesis), the mechanisms for incorporations, the effect of heteroatoms on the acid-base properties and the catalytic features of modified samples [1-10]. Relatively less attention was paid to the effect of treatment process on the porous properties of samples although the incorporation of heteroatoms, especially by the so-called post-synthesis, frequently changes the distribution of pore size. Recently, we incorporated Al, Ga and B atoms into zeolites (3 by the post-synthesis in an alkaline medium named alumination, galliation and boronation, respectively. It was found that different trivalent elements inserted into the [3 framework at quite different level. The heteroatoms with unsuitable atom size and poor stability in framework were less introduced, leading to that a considerable amount of framework silicon were dissolved under the action of base and the mesopores in zeolite crystal were developed. As a typical case, the boronation of zeolites (3 and the accompanied formation of mesopores are reported in the present paper. 

Relatively few studies have focused on influence of the acid/base properties of the support on the chemisorption of reactants on supported metal clusters. A NMR study by Tong et al.23 showed that the stretching frequency of CO chemisorbed on zeolite supported Pt particles correlates with the surface local density of states (LDOS) of the Pt. The LDOS also showed a correlation with the faujasite framework acidity, but an explanation of this correlation is lacking. Several infrared studies on similar supported Pt catalysts show that the mode of CO... 

The initial results obtained (258-263) using trivalent ion-exchanged zeolites as catalysts for thermolytic water splitting are quite encouraging. The simple two-step cycle, the good stability, and noncorrosive properties of the zeolite are all positive aspects. Further research toward a zeolite-based system which could operate at even lower temperatures would seem worth pursuing. 

Some excellent reviews exist on benzene alkylation.52 Comparison of Beta with other zeolites (USY 53 or MCM-22 and ZSM-5)54 shows that Beta seems to be the most active catalyst whereas MCM-22 shows the best overall properties combining a good activity with an excellent stability. Similar results are found for the zeolite-based cumene processes where zeolite Beta is used in the process developed by Enichem.52... 

Zeolites containing 3d transition-metal ions were considered in Beran et al. (109-112). The peculiarities of the donor-acceptor interactions of these cations located within six-membered rings with a zeolite lattice were discussed in terms of atomic charges, bond orders, and orbital energies. The redox properties of the cations, the acid-base properties of zeolites, and the dependence of these characteristics on the Si/Al ratio were discussed as well. The authors noted that the forms containing univalent copper and nickel ions should possess the highest electron-donor ability and consequently the... 

The most important feature of zeolites (and zeotypes), in the context of catalysis, is not their range of acid-base properties, since that is also available with amorphous alumino-silicates. It is the presence of a regular structure containing... 

A considerable amount of work had been done to understand the effects of the physico-chemical properties of the catalyst on its activity and selectivity. However, there is a paucity of information on the coke burning behavior ofdifferent FCC catalysts and its effect on catalyst properties. This gap is further widened by the advent of a variety of zeolite based catalysts, with widely different physico-chemical and morphological properties. 

It can be generally concluded that the works of many authors were confined to amorphous or a single zeolite based FCC catalyst. The effect of catalyst properties on regenerability has not received the due importance in the above studies. 

Table-I gives the properties of different steamed catalysts used in the present study. Catalyst AM is the amorphous catalyst while all others (Z1-Z4) are zeolite based catalysts. All the steamed catalysts have been analyzed (in ASAP-2000 of Micromeritics) for the surface area of micro and macro pores. In the present study, all the pores below 30 A are considered as micro pores while those above this are lumped into macro pores. The ratio of surface areas of micro to macro pores (Sz / Sm) is used in the data analysis.

Cobalt, copper and nickel metal ions were deposited by two different methods, ionic exchange and impregnation, on an amorphous silica-alumina and a ZSM-5 zeolite. The adsorption properties towards NH3 and NO were determined at 353 and 313 K, respectively, by coupled calorimetric-volumetric measurements. The average acid strength of the catalysts supported on silica-alumina was stronger than that of the parent support, while the zeolite-based catalysts had (with the exception of the nickel sample) weaker acid sites than the parent ZSM-5. The oxide materials used as supports adsorbed NO in very small amounts only, and the presence of metal cations improved the NO adsorption [70]. 

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