Copper based supported metal catalysts

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]... 

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]. 

Various methods, many with an eye towards industrial application, have been examined to accelerate Cannizzaro reactions. For example copper-silica catalysts,Na2S, Na2S203 or NaaSOs supported on AI2O3, and ultrasound all have been reported to accelerate certain Cannizzaro processes. An extremely promising development is the use of transition metal catalysts, which may be employed under neutral conditions in the absence of strong base. This permits the use of enolizable aldehydes like (28), which under basic conditions would immediately be consumed via aldol reactions. For example, in the presence... 

Low levels of SOj in the exhaust gas stream are known to lower the catalytic activity of noble metal-supported catalysts, although this effect is considerably less compared to base metal catalysts [19]. Iwamoto et al. [20] observed a sUght decrease of NO removal activity of the Cu- M-5 for NO reduction by C3H5 upon the addition of SOj to the feed gas stream. The conversion of NO at 300°C, however, completely recovered to the initial state upon termination of the SO2 feed. They suggested that the loss of the removal activity of the catalyst is probably due to the alteration of the copper ionic state on the catalyst surface but provided no evidence in support of this hypothesis. 

Neither of the base-metal oxide catalysts tested were active at low temperatures (see Figures 5 and 6), but CuO supported on alumina and silica exhibit rather low formation of acetaldehyde. This corresponds to the results presented by Rajesh and Ozkan (1993) who have tested the activity of catalysts containing either oxides of copper or chromium and also a combination of these two metal oxides supported on y-alumina pellets. The formation of acetaldehyde is slightly higher over CuO-Mn02. Catalysts supported on titania show the lowest light-off temperature for all the base-metal catalysts tested, but also the highest formation of acetaldehyde. 

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... 

---