Copper based supported metal

The shift of the half-wave potentials of metal ions by complexation is of value in polarographic analysis to eliminate the interfering effect of one metal upon another, and to promote sufficient separation of the waves of metals in mixtures to make possible their simultaneous determination. Thus, in the analysis of copper-base alloys for nickel, lead, etc., the reduction wave of copper(II) ions in most supporting electrolytes precedes that of the other metals and swamps those of the other metals present by using a cyanide supporting electrolyte, the copper is converted into the difficultly reducible cyanocuprate(I) ion and, in such a medium, nickel, lead, etc., can be determined. 

The replacement of vanadia-based catalysts in the reduction of NOx with ammonia is of interest due to the toxicity of vanadium. Tentative investigations on the use of noble metals in the NO + NH3 reaction have been nicely reviewed by Bosch and Janssen [85], More recently, Seker et al. [86] did not completely succeed on Pt/Al203 with a significant formation of N20 according to the temperature and the water composition. Moreover, 25 ppm S02 has a detrimental effect on the selectivity with selectivity towards the oxidation of NH3 into NO enhanced above 300°C. Supported copper-based catalysts have shown to exhibit excellent activity for NOx abatement. Recently Suarez et al and Blanco et al. [87,88] reported high performances of Cu0/Ni0-Al203 monolithic catalysts with NO/NOz = 1 at low temperature. Different oxidic copper species have been previously identified in those catalytic systems with Cu2+, copper aluminate and CuO species [89], Subsequent additions of Ni2+ in octahedral sites of subsurface layers induce a redistribution of Cu2+ with a surface copper enrichment. Such redistribution... 

Copper based catalysts have long been considered as the only effective methanol synthesis catalysts. However, Poutsma et al. (7) showed that palladium catalysts were active in methanol synthesis from CO-H. This latter metal had been previously considered as either almost inactive or active only for methane formation (8). Furthermore it is now known that both activity and selectivity can change drastically with the support. Vannice (9) observed that the methanation activity of a Pd/Al O was enhanced eighty and forty times compared to palladium black or Pd/SiO (or Pd/TiO ) respectively. The support effect on the selectivity was pointed out by many authors even at atmospheric pressure when the reaction temperature... 

This set of experiments establishes that pure copper metal, free of surface impurities, yields less than 10 8 kg of methanol per square meter of the catalyst per hour under the standard conditions outlined above. Such a yield is far below the specific activity of supported" copper-based catalysts, e.g., 3.63 x 10 5 kg CH3OH m 2 hr-1 for the Cu/ZnO = 30/70 catalyst (39), and shows that copper metal is a very poor catalyst for methanol synthesis at 75 atm at 250°C. 

The methanol is dehydrogenated in the gas phase around I90. at atmospheric pressure, in the presence of a copper-based catalyst on a support, promoted by other metals such as Zr, Zn. M etc... 

Cobalt, copper and nickel metal ions were deposited by two different methods, ionic exchange and impregnation, on an amorphous silica-alumina and a ZSM-5 zeolite. The adsorption properties towards NH3 and NO were determined at 353 and 313 K, respectively, by coupled calorimetric-volumetric measurements. The average acid strength of the catalysts supported on silica-alumina was stronger than that of the parent support, while the zeolite-based catalysts had (with the exception of the nickel sample) weaker acid sites than the parent ZSM-5. The oxide materials used as supports adsorbed NO in very small amounts only, and the presence of metal cations improved the NO adsorption [70]. 

Cerium-based catalysts have been successfully used in several processes. For example, ceria (Ce02) is used as an additive [ 1,2] in modem automotive exhaust catalysts. Ceria acts as an excellent oxygen store [3-5] in the catalyst, which is thus rendered a very effective catalyst for combustion [6]. Moreover, addition of ceria to the automotive exhaust catalysts minimises the thermally induced sintering of the alumina support and stabilises the noble metal dispersion [7]. Ceria also enhances nitric oxide dissociation when added to various supported metal catalysts [8], which is another important function of the automotive exhaust catalyst. Recent investigations by Harrison et al have shown that ceria doped with certain lanthanides and promoted with copper and chromium have catalytic activities comparable to that of the noble metal catalysts [9]... 

Chinchen et al. have reported that, as shown in Figure 10, the activity of a variety of copper-based catalysts for methanol synthesis is proportional to the specific copper surface area irrespective of the coexisting metal oxide (support). In other words, the methanol synthesis activities per unit copper surface area are identical. It is considered from the figure that there are two possible ways of improving the activity for methanol synthesis catalysts. These are... 

Hydrogen interaction with copper is an interesting border case since it processes a substantial barrier for the adsorption process and stiU is an interesting metal from a catalytic point of view. The catalyst used in the low temperature water gas shift reaction is based on metallic copper on a Zn/Al203 support whereby CO and water... 

The main OC families are based on the use of nickel, iron, copper, manganese as metal or some mixed metal oxides. The metal oxides are usually mixed with some material support to reduce the diffusion limitations inside the particles (by increasing the particle porosity), to improve the material stability and also increase the heat capacity. The most often used OCs are discussed briefly here. More information can be found in Adanez et al. [9], Hossain etal. [10] andLyngfelt etal. [11]. The main properties ofthe most often used OCs are listed in Table 5.1 [9, 11, 12]. 

A recent development was to prepare carbon based molecular sieves which are funcionalized with inorganic oxides and supported metals. The main objective is to combine the molecular sieving properties of the carbon with surface chemical and physical properties of the inorganic oxides in one composite structure. Sharma and Seshan [9] reported copper modified CMS for the selective removal of oxygen at temperatures below 200 C. At higher temperatures, oxygen can be reversible adsorbed only if present in trace amounts. 

Metal foam (see, for example. Figure 3.5) has already been discussed in the context of heat exchangers. Micro-reactors, highly relevant to the subject of small fuel cells, have also been introduced in earlier chapters. The construction of metal foam based methanol steam micro-reformers to generate hydrogen for polymer electrolyte membrane fuel cells (PEMFCs) has been reported and in Guangzhou, Chinese researchers have looked at laminated micro-reactors in which copper-based catalysts have been supported by metal foams (see Figure 11.11 Yu et al., 2007). 

The parallelism between the two reactions is somehow supported by the similarity of the catalysts, which are active at low temperature in the two reactions. The preferential oxidation (PROX) of CO in the presence of hydrogen represents an important step in the synthesis of pure hydrogen for application in low temperature fuel cells. Noble metals are active for this reaction at very low temperature (100-200°C). Commercial catalysts are typically based on Pt/y-Al203. Supported gold was quite recently discovered to act as an excellent catalyst for PROX as well as for the low temperature (200 K) CO oxidation in waste gases.Copper-based catalysts are also reported to be excellent for the PROX reaction. ... 

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