Preparation zeolite supported

Chemistry similar to that described above for iridium clusters has also been observed for rhodium clusters. Several authors [16-18] have prepared [Rh6(CO)i6] in NaY zeolite [R1i4(CO)i2] has also been formed [18], and each of these has been decarbonylated with minimal changes in the metal frame, as shown by EXAFS spectroscopy [18]. Thus there appears to be some generality to the method of forming small clusters in zeolite cages by synthesis of stable metal carbonyl precursors followed by decarbonylation. However, the method is limited. Attempts to use it to prepare zeolite-supported platinum clusters that are structurally simple and uniform have apparently not been successfiil. The literature of platinum carbonyl clusters in zeolites is not considered here because it is still contradictory. 

The microwave technique has also been found to be a potential method for the preparation of the catalysts containing highly dispersed metal compounds on high-porosity materials. The process is based on thermal dispersion of active species, facilitated by microwave energy, into the internal pore surface of a microporous support. Dealuminated Y zeolite-supported CuO and CuCl sorbents were prepared by this method and used for S02 removal and industrial gas separation, respectively [5], The results demonstrated the effective preparation of supported sorbents by micro-wave heating. The method was simple, fast, and energy-efficient, because the synthesis of both sorbents required a much lower temperature and much less time compared with conventional thermal dispersion. 

Pradhan, A.R., Macnaughtan, M.A., and Raftery, D. (2002) Preparation of zeolites supported on optical microfibers. Chem. Mater., 14, 3022-3027. 

In the preparation of faujasite zeolite-supported Pt-Re catalysts, bimetallic PtRe clusters have been reported to be predominantly formed when a carbonyl rhenium precursor (Re2(CO)io) is contacted with zeolite in which platinum has been previously introduced and reduced. The preexisting Pt clusters may act as nucleation sites. After reduction, these Pt-Re systems show a high selectivity to CH4 in the hydrogenolysis of n-heptane [58]. 

High nuclearity carbonyls Rh4(CO)i2 and Rhs(CO)i6 have been extensively used as precursors for the preparation of supported rhodium catalysts. Early studies reported the use of a great variety of supports that includes metal oxides [159-166], zeolites [101, 167], polymers [168] and modified-silica surface [169]. 

Table 10.6 shows the catalytic performances of the selective benzene oxidation on the zeolite-supported Re catalysts under steady-state reaction conditions [107]. Catalyhc activity and selectivity largely depended on the types of zeolites and the preparation methods. The Re catalysts prepared by CVD of MTO exhibited higher catalyhc achvity and phenol selechvity than those prepared by the convenhonal impregnation method as supports (Table 10.6). Physical mixing of MTO with the supports provided poor phenol synthesis.

A bifunctional platinum supported on -zeolite catalyst was also prepared for comparison with the molybdenum catalysts. The -zeolite support (Si/Al ratio = 12.5) was ion exchanged three times with NH4N03 (aq., 1 M), before drying, calcining in air (813 K, 3 h) and impregnating... 

Zeolite-supported Re catalysts have been synthesized by chemical vapor deposition (CVD) ofMTO (CH3Re03) (3) on various zeolites such as HZSM-5, H-Beta, H-USY and H-Mordenite. HZSM-5 samples with different A1 contents were prepared by a hydrothermal synthesis method. For comparison, conventional impregnated catalysts were also prepared by an impregnation method using an aqueous solution of NH4Re04. All catalysts were pretreated at 673 K in a flow of He before use as catalyst. 

Several supported Pt catalysts were prepared. The supports used are Mg hydrotalcite (HT), SiC>2, amorphous Si02-Al203 (ASA) and LTL zeolite. The support characteristics are shown in Table 1. 

Impregnation and ion-exchange methods for preparation of supported catalysts are discussed in detail in Section 2.2.1.1. Only ion exchange in the solid state as a novel method to prepare zeolite catalysts is described here. 

Different ways have been proposed to prepare zeolite membranes. A layer of a zeolite structure can be synthesized on a porous alumina or Vycor glass support [27, 28]. Another way is to allow zeolite crystals to grow on a support and then to plug the intercrystalline pores with a dense matrix [29], However, these two ways often lead to defects which strongly decrease the performance of the resulting membrane. A different approach consists in the direct synthesis of a thin (but fragile) unsupported monolithic zeolite membrane [30]. Recent papers have reported on the preparation of zeolite composite membranes by hydrothermal synthesis of a zeolite structure in (or on) a porous substrate [31-34]. These membranes can act as molecular sieve separators (Fig. 2), suggesting that dcfcct-frcc materials can be prepared in this way. The control of the thickness of the separative layer seems to be the key for the future of zeolite membranes. 

Series of zeolite-supported iron-containing catalysts with weight percent iron (% Fe) varying from 1 to 17% Fe have been prepared from Fe3(CO) 2 and the synthetic zeolites ZSM-5, mordenite and 13X by an extraction technique. The zeolites ZSM-5 and mordenite were used in the acid form, 13X in the sodium form. 

It is concluded from the characterization studies, that the extraction technique which we have employed for the preparation of zeolite-supported iron catalysts results in the formation of highly dispersed, small particle-sized Y-Fe2°3 on the support surface and, in addition, a small amount ( 1%) of iron present as a spe-... 

Fourth, by careful choice of the zeolite support in the preparation of a bifunctional catalyst for synthesis gas conversion, the product distribution, particularly for hydrocarbons, may be controlled. This conclusion is of importance in the design of catalysts for the production of liquid transportation fuels from synthesis gas. 

Recent research on the elementary steps during preparation of zeolite-supported metals has helped to understand the genesis of these particles in considerable detail. For the best studied systems the goal of preparing catalysts by design has been achieved (69-77). 

Basaldella El, Kikot A, Quincoces CE, and Gonzalez MG. Preparation of supported Cu/ZSM-5 zeolite films for DeNO(x) reaction. Mater Lett 2001 51(4) 289-294. 

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