Single-zeolite catalyst

Reactor type Single-channel chip micro reactor Zeolite catalyst layer thickness 3 pm... 

A dual-bed catalyst system has been developed to tackle the key problems in benzene product impurity during heavy aromatics transalkylation processing over metal-supported zeolite catalysts. It was found that by introducing zeolite H-Beta as a complementary component to the conventional single-bed Pt/ZSM-12 catalyst, the cascaded dual-bed catalyst shows synergistic effect not only in catalytic stability but also in adjustments of benzene product purity and product yields and hence should represent a versatile catalyst system for heavy aromatics transalkylation. 

Characterization is an integral tool for the development of new zeolites and for the development and commercialization of zeolitic catalysts and adsorbents. Single techniques are not sufficient as they rarely provide full details of the system. A combination of selective characterization techniques is required. As suggested by Deka [1] even a single acidity characterization method may be insufficient to provide the necessary detailed information to understand the zeolite acid sites. Thus according to Deka the combination of different experimental techniques is required to shorten the time of development for a new catalyst. 

A variant on the ship-in-a-bottle approaches described above is to react a preformed catalyst with the zeolite framework. This is analogous to procedures developed for immobilizing organometallic and coordination compounds on surfaces, but occurs within zeolite pores. These compounds that have reacted with the external surface must be removed, along with those adsorbed on the surface, to produce a true single-site catalyst. Two examples, illustrating different synthetic approaches, are discussed below. 

The simplest supported catalysts are mononuclear metal complexes, exemplified by industrial supported metallocene catalysts, used (with promoters) for alkene polymerization these are the so-called single-site catalysts that are finding wide industrial applications (Kristen, 1999 Kaminsky, 1999 Roscoe et al., 1998). The most common supports are metal oxides and zeolites. The metals in these complexes range from oxophilic (e.g., Zr and Ta) to noble (e.g., Rh). Supported metal complexes are stabilized by ligands—in addition to those provided by the support—such as hydride (H), hydrocarbons, and carbonyl (CO). In a typical supported metal complex, the metal is present in a positive oxidation state. Although some such complexes are relatively stable, most are, befitting their roles as catalysts, highly reactive and air- and moisture-sensitive. 

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. 

The pore diameters of MFI-type zeolites are comparable to the size of many commercially important molecules, such as aromatics or linear or branched hydrocarbons [1]. Thus, the study of the difiusion of reactive molecules in the channel system of zeolite catalysts is of considerable interest for the understanding of the catalyst performance. A variety of methods has been developed and applied to the measurement of diffii-sion coefficients, amongst others gravimetric techniques [2], neutron scattering [3], NMR [4] and Frequency Response [5]. The FTIR technique offers the possibility to study sorption and sorption kinetics under conditions close to those of catalytic experiments. By the use of an IR microscope, single crystals have become accessible to the FTIR technique. 

Figure 2 shows the XANES spectra of the Ti-oxide/Y-zeolite catalysts. The ex-Ti-oxide/Y-zeolite exhibits an intense single preedge peak, indicating that the Ti-oxide species in this catalyst has a tetrahedral coordination [9]. 

Alkylation activity recovery from a completely deactivated USY zeolite catalyst was next examined in a single-pass reaction system employing SC... 

One limitation of the single-events theory consists in considering the surface intermediates, carbocations and/or activated compounds, as if they were free species or radicals. In the important case of small-pore zeolitic catalysts, this limited representation of the catalytic act is no longer valid since the shape selectivity problems, introduced by the geometry and confinement of zeolitic cages, are ignored. 

Styrene (SM) can be synthesized in a single step via alkylation of toluene with methanol which offers significant advantages in raw material costs and energy consumption as compared to the benzene to styrene via ethylbenzene process. This single-step process is carried out at a temperature of 400°C and uses a cesium-boron type X zeolite catalyst. The reaction is [31] ... 

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