Copper unsupported

Minimum baffle spacing is generally one-fifth of the shell diameter and not less than 50.8 mm (2 in). Maximum baffle spacing is hm-ited by the requirement to provide adequate support for the tubes. The maximum unsupported tube span in inches equals 74 dP (where d is the outside tube diameter in inches). The unsupported tube span is reduced by about 12 percent for aluminum, copper, and their alloys. 

Based on the previously described silver complex [Au2Ag2(Q)f,s)4(MeCN)2 , the same reaction with CuCl in acetonitrile but with addition of an equivalent of pyrimidine leads to the polymeric [CuAu(C6F5)2(MeCN)((J.2-C4H4N2)]n [66]. The polymerization of this complex is produced by covalent copper-pyrimidine bonds. The environment of the copper centers also comprises unsupported gold-copper interactions of 2.8216(6) A and one molecule of acetonitrile, leading to a distorted tetrahedral arrangement (see Figure 6.26). 

Powders possessing relatively high surface area and active sites can be intrinsically catalytically active themselves. Powders of nickel, platinum, palladium, and copper chromites find broad use in various hydrogenation reactions, whereas zeolites and metal oxide powders are used primarily for cracking and isomerization. All of the properties important for supported powdered catalysts such as particle size, resistance to attrition, pore size, and surface area are likewise important for unsupported catalysts. Since no additional catalytic species are added, it is difficult to control active site location however, intuitively it is advantageous to maximize the area of active sites within the matrix. This parameter can be influenced by preparative procedures. 

Metallodendrimer Go-20 was used as a catalyst in the 1,4-addition reaction of diethylzinc to 2-cyclohexenone in a variety of solvents. The results obtained showed that this dendritic catalyst provides activities similar to or even higher than those observed for the unsupported aminoarenethiolato copper(I) complexes, depending on the solvent used. Applying Go-20, this reaction could also be performed using a solvent as apolar as hexane, whereas the unsupported complexes are not soluble in this medium. 

The copper surface areas of fresh (S ) and used (S ) catalysts are demonstrated in Table l. The ratio of S1/S0 exhibits the extent of copper surface area reduced after reaction. The copper surface areas reduce after dehydrogenation reaction. This indicates that sintering occurs in reaction process for all of the catalysts. Chromium promoted catalysts have higher fresh copper surface areas than the unpromoted one as shown in Table 1. The previous results [5] indicated that the catalyst with Cr/Cu molar ratio of 1/10 had the highest stability for unsupported catalyst nevertheless, the catalyst with Cr to Cu molar ratio of 1/40 is the most stable one in Si02-supported case. The stability of chromium promoted catalyst decreases when the Cr/Cu molar ratio increases. 

The early conflicting reports on the activity of pure copper metal could not be reconciled without the simultaneous or concurrent measurements of activity, surface area, and surface composition. Moreover, it became evident that it is important to use unsupported copper as the reference material to avoid support-metal interactions that may influence the catalytic properties of the latter. 

Aside from the recently described Cu/Th02 catalysts, copper on chromia and copper on silica have been reported to catalyze methanol synthesis at low temperatures and pressures in various communications that are neither patents nor refereed publications. It is not feasible to critically review statements unsupported by published data or verifiable examples. However, physical and chemical interactions similar to those documented in the copper-zinc oxide catalysts are possible in several copper-metal oxide systems and the active form of copper may be stabilized by oxides of zinc, thorium, chromium, silicon, and many other elements. At the same time it is doubtful that more active and selective binary copper-based catalysts than... 

Elemental copper can be used as an unsupported catalyst for the oxidative dehydrogenation of alcohols to their respective aldehydes. There are two main reaction paths partial oxidation to formaldehyde and total oxidation to carbon dioxide, which is thermodynamically favored. The... 

The activity of the thus prepared Cu(oxide)/SiC>2 catalyst in the oxidation of carbon monoxide is represented in Fig. 9.13. It can be seen that the activity of the fresh catalyst before reduction is rather low. In spite of the very good dispersion (high surface area), the conversion at e.g. 180°C is much lower than that of unsupported copper oxide and the less well dispersed copper oxide. However, reduction and reoxidation leads to a much higher activity, cf. Fig. 9.14. Apparently, then, the activity of copper ions in a copper hydrosilicate is much lower than that of those in an oxide. As the dispersion remains very high in the transformation of the one phase into the other, a high catalytic activity can therefore be achieved. 

Reinhard D, Hall BD, Berthoud P, Valkealahti S, Monot R (1998) Unsnpported nanometer-sized copper clusters studied by electron diffraction and molecular dynamics. Phys Rev B 58 4917-4926 Reinhard D, Hall BD, Berthoud P, Valkealahti S, Monot R (1997) Size-dependent icosahedral-to-fcc stmcture change confirmed in unsupported nanometer-sized copper clusters. Phys Rev Letters 79 1459-1462... 

This review is followed by a consideration of some of the features characteristic of hydrocarbon reactions on catalysts comprising individual metals from Groups VIII and IB of the periodic table. Finally, the activities of a series of unsupported nickel-copper alloys for hydrogenolysis and dehydrogenation reactions are discussed. These latter studies were made to obtain information on the selectivity phenomenon with bimetallic catalysts of known structure. The nickel-copper alloys were characterized by a variety of chemical and physical probes. 

Figure 2.8 Isotherms for total hydrogen adsorption (circles) and weakly adsorbed hydrogen (squares) at room temperature on unsupported nickel and copper catalysts and on a nickel-copper alloy catalyst (6). (Reprinted with permission from Academic Press, Inc.)...

The surface properties of unsupported ruthenium-copper aggregates are considered in this chapter. In a subsequent chapter on bimetallic cluster catalysts, the properties of supported ruthenium-copper and osmium-copper catalysts are considered in detail. 

Recent work conducted in the laboratory of G. Ertl in Munich has extended the investigations on the ruthenium-copper system to include single crystal specimens (18-20). The results of the work are in excellent accord with those obtained in our laboratory on unsupported ruthenium-copper aggregates and on supported ruthenium-copper clusters as well. Our work on supported bimetallic clusters of ruthenium and copper is discussed in detail in the following chapter. 

A most satisfactory comparison of the activities of supported and unsupported catalysts of silver, copper, and nickel may be obtained from the results of experiments made by Faith and Keyes,803 who worked with methanol and ethanol. The fact that uniform methods of catalyst preparation, support, and size, and uniform methods of operations were used adds much to the value of the results. In all cases the catalyst mass was 45 mm. long by 12 mm. in diameter, the alcohol saturator was maintained at 45° C. for ethanol and at 36° C. for methanol, and the temperature of the hottest point in the catalyst mass was determined with a thermocouple embedded in the mass. In the case of ethanol oxidation the highest conversions to acetaldehyde per pass were obtained under the following conditions (1) silver gauze catalyst flow rate 0.57 liters per minute catalyst temperature 515° C., 80.6 per cent conversion to aldehyde 13.3 per cent conversion to carbon dioxide and 3.2 per cent conversion to add, (2) silver oxide supported on asbestos flow rate 0.37 liters per minute catalyst temperature 595° C. (conversions as above) 72.3 per cent 14.5 per cent 2.9 per cent, (3) copper turnings catalyst flow rate 0.62 liters per minute catalyst temperature 512° C. (conversions) 78.0... 

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