Carriers, catalyst

Although supported Pd catalysts have been the most extensively studied for butadiene hydrogenation, a number of other catalysts have also been the object of research studies. Some examples are Pd film catalysts, molybdenum sulfide, metal catalysts containing Fe, Co, Ni, Ru, Rh, Os, Ir, Pt, Cu, MgO, HCo(CN) on supports, and LaCoC Perovskite. There are many others (79—85). Studies on the weU-characteri2ed Mo(II) monomer and Mo(II) dimer on siUca carrier catalysts have shown wide variations not only in catalyst performance, but also of activation energies (86). 

Van Hardeveld and Hartog describe the effect of metal particle size on the properties of a metal on carrier catalyst. They have related the adsorptive and catalytic properties of metal crystals to crystal size and to the structure of the crystal surface. 

The screening of carriers, catalyst composition, particle sizes and shapes showed indeed, that a much more active catalyst could be made with Cs as a secondary promoter for the beds downstream the intermediate absorption tower. The best candidates were selected, and some m3 of each recipe were produced as 9-mm and 12-mm Daisy extrudates in a successful commercial-scale test production. The activities were as expected from the previous development work, and a 30 day activity test also confirmed it to be stable during this period. 

Uses Solvent for liquids, gases, vinyl resins, wire enamels polyacrylic fibers gas carrier catalyst in carboxylation reactions organic synthesis (manufacture of aldehydes, amides, amines, esters, heterocyclics). 

Another possibility of transforming indirectly alcohols into alkyllithium compounds consists in nsing the corresponding sulfates. Alkyl sulfates 60 were lithiated using naphthalene (4%) as the electron carrier catalyst in THF at —78 °C yielding two equivalents of the corresponding alkyllithinm 61. Further addition of an electrophile at —78 to 0°C led to the formation, after hydrolysis, of the final prodncts 20 (Scheme 22) ... 

A special case of functionalized aryllithium reagents appears when the corresponding aryl group bears a ketal moiety at the benzylic position due to the lability of the benzyUc carbon-oxygen bonds. However, working under Barbier-type conditions and using naphthalene (10%) as the electron carrier catalyst, the reaction of chlorinated materials 242 afforded, after hydrolysis with water, the corresponding polyfunctionalized products 243 (Scheme 81). ... 

The same process shown in Scheme 88 starting from different 2-substituted oxetanes and using biphenyl as the electron-carrier catalyst under THF reflux has been used to prepare regioselectively substituted primary alcohols. On the other hand, the combination of a DTBB-catalyzed ca 20%) lithiation with triethylaluminium in TFIF at —78 °C has been used for the transformation of strained oxetanes to substituted di- and triquinanes through a rearrangement process . An example is given in Scheme 89 for the transformation of oxetane 299 into the product 302 through radicals 300 and 301. 

Electron donor Photosensitizer Electron carrier Catalyst Ref. 

Catalyst carrier Catalyst code Active component 1 (wt.%) Active component 2 (wt.%)... 

Relatively simple syntheses for the majority of macrobicyclic complexes, compared with conventional techniques for the preparation of macrocyclic compounds, have made such complexes attractive not only for research, but also for practical application as electron carriers, catalysts for electro- and photochemical processes, and some other purposes (e.g., protein redox titrants, biological electrochemical mediators, and ionophore and electrode modifiers). 

Phase Solvent, carrier Catalyst" Temperature, pressure C3H6/O2/H2/ carier, SV ml gcat h C3H6 conversion % PO selectivity % POSTY gpo kgcat h Reactor Notes Referi... 

In syntheses of fine chemicals, heterogeneously catalyzed enantioselective hydrogenations have been gradually developing into a topic of great interest over the past few years, as enantiomerically pure substances are required in pharmaceuticals, biochemistry and food technology. For these purposes, chirally modified metal/carrier catalysts have been used, but the effect of the catalytic system is little known [1-8]. 

Having chosen appropriate chiral auxiliary, solvent and reaction parameters, it is necessary to apply tailor-made metal/carrier catalysts in order to optimize enantioselectivity and catalytic activity. Since the carrier material significantly influences the properties of the active Pt particles. 

This paper deals with the asymmetric hydrogenation of ethyl pyruvate to ethyl lactate showing a high enantiomeric excess in favour of the R-enantiomer over (-)cinchonidine modified Pt/carrier catalysts. Due to their regular structures, zeolites in particular have been used as carrier materials. 

The specific surface areas of the Pt/carrier catalysts were determined by volumetric Nj adsorption at 77 K, and the specific Pt surface areas were derived from volumetric CO chemisorption measurements at 298 K (as described in Ref [8]). The results are shown in Table 1. The values of the pore access diameters are obtained from Ref [9]. 

The hydrogenations were performed at 293 K and an initial hydrogen pressure of 7.1 MPa under constant stirring at 1200 min 10 ml ethyl pyruvate were hydrogenated in a mixture of 20 ml solvent (acetic acid or cyclohexane), 5 mg (-)cinchonidine (chiral auxiliary) and 100 mg Pt/carrier catalyst. 

Figure 5. CO TPD spectra of the prepared Pt/carrier catalysts (P specific desorption pressure)...

Enantiomeric excess and catalytic activity of the asymmetric hydrogenation of ethyl pyruvate over (-)cinchonidine modified Pt/carrier catalysts depend significantly on the specific Pt surface area This is due to the morphology of the Pt particles and to surface chemical Pt/support interaction. Thus, reaction pathway control is possible by varying these parameters. 

R. Gauguin, M. Graulier and D. Pappee, Thermally Stable Carriers, Catalysts for Control of Automotive Pollutants, Ed. J. E. McEvoy, ACS Series 143, American Chemical Society, Washington D.C., 1975, pp 147-160. 

The primary particles forming the carrier itself need to be inert in respect to the chemicals used for impregnation and during reaction. In addition, the shape and structure of the carrier must be defined and uniform and the strength high to guarantee good permeability of the activated carrier (catalyst) bed. Little or no mechanical breakdown must occur due to the overburden pressure in the column. 

The nickel content of carrier catalysts is usually 10-40%. Nickel catalysts are generally reduced at 300-500° but nickel mixed catalysts, containing metals nobler than nickel, can be reduced at lower temperatures, e.g., copper-nickel mixed catalysts168 as low as 200-300°. 

The following nickel-carrier catalysts have been described nickel-kieselguhr,169 nickel-pumice,170 nickel-kieselguhr containing thorium oxide,171 nickel on magnesium oxide, barium oxide, or beryllium oxide,172 nickel on aluminum oxide,173 and nickel-zinc oxide-barium oxide-chromium oxide.174 Other carriers for nickel catalysts are active charcoal, silica, fuller s earth, and oxides such as magnesia, alumina, and bauxite. 

For many hydrogenations the carrier catalyst is stirred into the substance to be hydrogenated and the mixture is hydrogenated the catalyst must then be reduced before hydrogenation of the compound can occur. 

Other classes of catalysts studied at Union Carbide include simple perovskites, metal/molecular sieves, and catalysts based on Pr/Ce oxygen carriers. catalysts containing silver showed unusually high Cj selectivities, demonstrating the concept of enhanced surface reactions. 

S Development of Unstructured Catalytic Packing for Reactive Distillation Processes 1199 Table 8.3 Selected carrier materials suitable for the preparation of polymer/carrier catalysts... 

Table 8.4 Requirements for the Polymerization process of polymer/carrier catalysts...

Preparation of Sulfonated Ion-Exchange Polymer/Carrier Catalysts... 

By precipitation polymerization polymer/carrier catalysts with different properties were prepared. Table 8.6 gives properties of some samples. 

Table 8.6 Properties of the prepared and tested polymer/carrier-catalysts. The degree of cross-linking is 7.5% by weight for all samples, balanced with styrene...

In RD processes isothermal operation of the catalyst bed is not possible. At the top of the column temperatures in the range of 60 °C are common, with higher temperature towards the bottom. Higher temperatures enhance the reaction more than mass transfer. Therefore mass-transport phenomena will have more pronounced effects at higher temperatures. We tested the catalysts at temperatures of 60, 75, and 90 °C. The results are shown in Fig. 8.13 and Fig. 8.15 for polymer/carrier catalysts with different polymer content. GFP-15 is a catalyst with low polymer content GFP-12 has twice the polymer content of GFP-15. GFP-15 was chosen because it shows the classical MTBE kinetic pattern. GFP-12 was tested in an RD column. 

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