Catalyst preparation active metal

During the last few decades, many efforts have been realized for enhancing the MSR process, and some research fields are stiU ongoing. One of these is devoted to improve Ni-based catalyst performance by modifying the type of support, introducing promoters and additives and trying to identify the type of catalyst more durable. Moreover, deeper studies are also addressed toward the effect of catalyst preparation, active metal properties, and the support role on the catalyst performance. 

Catalysts. A batch of y-alumina extrudates was prepared. Active metals were incorporated by impregnating the extrudates with corresponding solutions of the metal salts. The characteristics of the catalysts are presented in Table III. 

Aluminum oxide itself catalyzes the metathesis reaction of propylene, although its activity is low. Catalysts that are obtained from oxides are active at temperatures ca 100 K higher than catalysts prepared from metal carbonyls. Compounds deposited on silica are catalytically active at temperatures which are higher by ca 200 K than compounds supported on aluminum oxide. However, because of the Si02 support these catalysts are more resistant to poisoning by polar compounds. Heterogeneous catalysts must be activated at 390-870 K before use. Catalysts obtained from metal carbonyls and alkyl compounds require lower temperatures of activation. Supported allyl complexes of Mo, W, and Re need no activation. 

A preparation of designed catalyst is one of the interest subjects to understand the catalysis. Efforts have been paid for the development of unique preparation method[1] those are metal cluster catalysts derived from metal carbonyls, tailored metal catalysts through organometallic processor and ultra-fine metal particle catalysts prepared by metal alkoxides, etc. These preparation methods are mainly concentrated to design the active sites on support surfaces. However, the property of support itself is also a dominant factor in order to conduct smoothly the catalytic reaction. It is known that some supports are valuable for the improvement of selectivity. For example, zeolites are often used as catalysts and supports for their regular pore structures which act effectively for the shape selective reaction[2]. In order to understand the property of support, the following factors can be pointed out besides the pore structure structure, shape, surface area, pore size, acidity, defect, etc. Since these are strongly correlated to the preparation procedure, lots of preparation techniques, therefore, have been proposed, too. Studies have been still continued to discover the preparation method of novel materials as well as zeolites[3]. 

Fig. 6. Dependence of the hydrogenation activity on the Fe2p/Si2p XPS intensity ratios for Fe-Cu(7 3)/Si02 precursor (O) and the reduced catalyst ( ) prepared from metal sulfates.

Catalysis. Ion implantation and sputtering in general are useful methods for preparing catalysts on metal and insulator substrates. This has been demonstrated for reactions at gas—soHd and Hquid—soHd interfaces. Ion implantation should be considered in cases where good adhesion of the active metal to the substrate is needed or production of novel materials with catalytic properties different from either the substrate or the pure active metal is wanted (129—131). Ion beam mixing of deposited films also promises interesting prospects for the preparation of catalysts (132). 

There are, however, continuing difficulties for catalytic appHcations of ion implantation. One is possible corrosion of the substrate of the implanted or sputtered active layer this is the main factor in the long-term stabiHty of the catalyst. Ion implanted metals may be buried below the surface layer of the substrate and hence show no activity. Preparation of catalysts with high surface areas present problems for ion beam techniques. Although it is apparent that ion implantation is not suitable for the production of catalysts in a porous form, the results indicate its strong potential for the production and study of catalytic surfaces that caimot be fabricated by more conventional methods. 

Ethylene Oxide Catalysts. Of all the factors that influence the utihty of the direct oxidation process for ethylene oxide, the catalyst used is of the greatest importance. It is for this reason that catalyst preparation and research have been considerable since the reaction was discovered. There are four basic components in commercial ethylene oxide catalysts the active catalyst metal the bulk support catalyst promoters that increase selectivity and/or activity and improve catalyst life and inhibitors or anticatalysts that suppress the formation of carbon dioxide and water without appreciably reducing the rate of formation of ethylene oxide (105). 

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

Since the catalytically active phase is frequently quite expensive (e.g. noble metals) it is clear that it is in principle advantageous to prepare catalysts with high, approaching 100%, catalyst dispersion Dc. This can be usually accomplished without much difficulty by impregnating the porous carrier with an aqueous solution of a soluble compound (acid or salt) of the active metal followed by drying, calcination and reduction.1... 

Metal-assisted enantioselective catalytic reactions are one of the most important areas in organic chemistry [1-3]. They require the appropriate design and the preparation of chiral transition metal complexes, a field also of major importance in modern synthetic chemistry. These complexes are selected on both their ability to catalyze a given reaction and their potential as asymmetric inducers. To fulfill the first function, it is absolutely required that the catalysts display accessible metal coordination sites where reactants can bind since activation would result from a direct interaction between the metal ion... 

Both PtRu/MgO catalysts prepared from cluster precursor and organometallic mixture were active for ethylene hydrogenation. The apparent activation energy of the former catalyst obtained from the Arrhenius plot during -40 to -25°C was 5.2 kcal/mol and that of the latter catalyst obtained during -50 to -30°C was 6.0 kcal/mol. The catalytic activity in terms of turn over frequency (TOP) was calculated on the assumption that all metal particles were accessible for reactant gas. Lower TOP of catalyst prepared from cluster A at -40°C, 57.3 x lO" s" was observed probably due to Pt-Ru contribution compared to that prepared from acac precursors. 

Industrially, the perfluoroalkyl iodides by telomerization are mostly made by a batch system using peroxide initiators. However, the difficulty of mass production, and the production of hydrogen-containing byproducts in the process are disadvantageous [4]. In this study, a continuous process for the preparation of perfluoroalkyl iodides over nanosized metal catalysts in gas phase and the effects of the particle size on the catalytic activities of different the preparation methods and active metals were considered. 

As can be seen in table 1, with different preparation methods and active metals, the average size of the copper particle for the catalysts A and D were 20.3 nm and 50.0 nm. While those of the catalysts B and C were 51.3 nm and 45.4 run, respectively. CuO, non-supported metal oxide, made by impregnation is sintered and cluster whose particle size was 30 pm. The water-alcohol method provided more dispersed catalysts than the impregnation method. 

Catalyst Active Metal Preparation Method Loading amount of metal (wt%) Particle Size (nm)... 

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