Hydrogenation catalysts copper/zinc oxides

Hydrogenation. Gas-phase catalytic hydrogenation of succinic anhydride yields y-butyrolactone [96-48-0] (GBL), tetrahydrofiiran [109-99-9] (THF), 1,4-butanediol (BDO), or a mixture of these products, depending on the experimental conditions. Catalysts mentioned in the Hterature include copper chromites with various additives (72), copper—zinc oxides with promoters (73—75), and mthenium (76). The same products are obtained by hquid-phase hydrogenation catalysts used include Pd with various modifiers on various carriers (77—80), Ru on C (81) or Ru complexes (82,83), Rh on C (79), Cu—Co—Mn oxides (84), Co—Ni—Re oxides (85), Cu—Ti oxides (86), Ca—Mo—Ni on diatomaceous earth (87), and Mo—Ba—Re oxides (88). Chemical reduction of succinic anhydride to GBL or THF can be performed with 2-propanol in the presence of Zr02 catalyst (89,90). 

Low-pressure methanol synthesis relies almost exclusively on catalysts based on copper, zinc oxide, and alumina. The catalysts are produced by ICI (now Johnson Matthay), Siidchemie (now Clariant), Haldor Topsoe, in the past also by BASF, and other chemical enterprises and contain 50-70 atomic % CuO, 20%-50% ZnO, and 5%-20% Al203. Instead of alumina, chromium oxide and rare earth oxides have also been used. The mixed oxide catalysts are usually shipped as 4-6 mm cylindrical pellets with specific surface area of 60-100 m2/g. The catalysts are activated in situ with dilute hydrogen, often derived from off-gases from synthesis gas... 

Saito M, et al. Development of copper/zinc oxide-based multicomponent catalysts for methanol synthesis from carbon dioxide and hydrogen. Appl Catal A Gen. 1996 138(2) 311—18. 

The hydrogenation of an unsaturated ester to an unsaturated alcohol may be possible over zinc-chromium oxide as catalyst, although the catalyst is known to be much less active for the usual ester hydrogenations than copper-chromium oxide. Ethyl or butyl (eq. 10.25) oleates were hydrogenated to octadecenol in yields of over 60% with a zinc-chromium oxide at 280-300°C and 20 MPa H2.16 The butyl ester was much preferred to the ethyl ester, since it was difficult to separate the ethyl ester from the alcohol product because of their similar boiling points. 

Keywords Methanol oxidation, hydrogen production, copper-zinc catalysts, fuel cells, activity... 

Kim and Kwon described a microreactor, heated by electricity, which carried a copper/zinc oxide catalyst [46]. About 4 mL min of hydrogen was produced by the reactor. At a reaction temperature of 300 °C and an S/C ratio of 1.1, full methanol conversion was achieved. Subsequently the same group developed a chip-like... 

Hydrogenation is generally carried out at tanperatures of 250-280°C and pressures of 20-25 MPa. Catalysts include zinc oxide in conjunction with aluminum oxide, chromium oxide, or iron oxide, and possibly, other promoters copper chromite whose activity has been reduced by the addition of cadmium compounds and cadmium oxide on an alumina carrier. Selective hydrogenation can also be carried out in a homogenous phase with metallic soaps as catalysts. 

Figure 4.6 Hydrogen yield versus methanol conversion and carbon monoxide content in the dry reformate for a commercial copper/zinc oxide catalyst [154],...

Partial oxidation of methanol is less frequently reported in the open literature. Cubeiro et al. investigated the performance of palladium/zinc oxide, palladium/ zirconia and copper/zinc oxide catalysts for partial oxidation of methanol in the temperature range between 230 and 270 °C (194j. Increasing selectivity towards hydrogen and carbon dioxide was achieved with increasing conversion, while selectivity towards steam and carbon monoxide decreased. The palladium/zinc oxide catalyst showed lower selectivity towards carbon monoxide compared with the palladium/zirconia catalyst. However, the lowest carbon monoxide selectivity was determined for the copper/zinc oxide catalyst. 

Precious metal based water-gas shift catalysts have zero reaction order for carbon monoxide below 300 ° C, which means that the rate of conversion is not affected by the carbon monoxide concentration in the low temperature range [57,303]. This is not the situation for the copper/zinc oxide catalysts described above [304]. However, the products carbon dioxide and hydrogen have an inhibiting effect on the reaction in the low temperature range for both types of catalysts [305, 304]. Many publications in the field of water-gas shift catalysts do not take these effects into consideration, which impairs the applicability of the results considerably. Frequently only carbon monoxide and steam are fed to the catalyst samples and the activity is determined while ignoring the effects of product inhibition. 

Kim and Kwon described methanol conversion of greater than 80% in their electrically heated microreactor, which carried a copper/zinc oxide catalyst [143]. About 4mLmin hydrogen were produced by the reactor. At 300 °C reaction temperature and S/C 1.1, full conversion of the methanol was achieved. However, the weight hourly space velocity of about 13 L (h gcat) was rather low, as is typical for copper/zinc oxide catalysts. 

Emonts et al. described the combination of the resulting 50-kW reformer with a hydrogen separation membrane system (see also Section 7.4) and a 1-kW Siemens PEM fuel cell to give a complete fuel processor/fud cdl system [50]. The breadboard system still required a footprint of 3 m. A flow scheme of the system along with a photograph is provided in Figure 9.3 3 kg of a copper/zinc oxide catalyst were... 

Chinchen, G.C., Denny, P.J., Parker, D.G., Spencer, M.S., and Whan, D.A. (1987a) Mechanism of methanol synthesis from carbon dioxide/carbon monoxide/hydrogen mixtures over copper/zinc oxide/alumina catalysts use of carbon-14-labeled reactants. Appl. Catal, 30, 333-338. 

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