Zinc oxide catalysts

This reaction is first conducted on a chromium-promoted iron oxide catalyst in the high temperature shift (HTS) reactor at about 370°C at the inlet. This catalyst is usually in the form of 6 x 6-mm or 9.5 x 9.5-mm tablets, SV about 4000 h . Converted gases are cooled outside of the HTS by producing steam or heating boiler feed water and are sent to the low temperature shift (LTS) converter at about 200—215°C to complete the water gas shift reaction. The LTS catalyst is a copper—zinc oxide catalyst supported on alumina. CO content of the effluent gas is usually 0.1—0.25% on a dry gas basis and has a 14°C approach to equihbrium, ie, an equihbrium temperature 14°C higher than actual, and SV about 4000 h . Operating at as low a temperature as possible is advantageous because of the more favorable equihbrium constants. The product gas from this section contains about 77% H2, 18% CO2, 0.30% CO, and 4.7% CH. ... 

Miscellaneous Reactions. Ahyl alcohol can be isomerized to propionaldehyde [123-38-6] in the presence of sohd acid catalyst at 200—300°C. When copper or alumina is used as the catalyst, only propionaldehyde is obtained, because of intramolecular hydrogen transfer. On the other hand, acrolein and hydrogen are produced by a zinc oxide catalyst. In this case, it is considered that propionaldehyde is obtained mainly by intermolecular hydrogen transfer between ahyl alcohol and acrolein (31). 

A AlI lation. A number of methods are available for preparation of A/-alkyl and A[,A/-dialkyl derivatives of aromatic amines. Passing a mixture of aniline and methanol over a copper—zinc oxide catalyst at 250°C and 101 kPa (1 atm) reportedly gives /V-methylaniline [100-61-8] in 96% yield (1). Heating aniline with methanol under pressure or with excess methanol produces /V, /V-dimethylaniline [121 -69-7] (2,3). 

High pressure processes P > 150 atm) are catalyzed by copper chromite catalysts. The most widely used process, however, is the low pressure methanol process that is conducted at 503—523 K, 5—10 MPa (50—100 atm), space velocities of 20, 000-60,000 h , and H2-to-CO ratios of 3. The reaction is catalyzed by a copper—zinc oxide catalyst using promoters such as alumina (31,32). This catalyst is more easily poisoned than the older copper chromite catalysts and requites the use of sulfiir-free synthesis gas. 

The dehydrogenation reaction is carried out using either copper or zinc oxide catalyst at approximately 450-550°C. A 95% yield is obtained ... 

Lebedev A one-step process for converting ethanol, derived from carbohydrates, to butadiene, using a mixed alumina/zinc oxide catalyst at approximately 400°C ... 

N2. Sulfur containing odorants (mercaptans, disulfides, or commercial odorants) are added for leak detection. Because neither fuel cells nor commercial reformer catalysts are sulfur tolerant, the sulfur must be removed. This is usually accomplished with a zinc oxide sulfur polisher and the possible use of a hydrodesulfurizer, if required. The zinc oxide polisher is able to remove the mercaptans and disulfides. However, some commercial odorants, such as Pennwalf s Pennodorant 1013 or 1063, contain THT (tetrahydrothiophene), more commonly known as thiophane, and require the addition of a hydrodesulfurizer before the zinc oxide catalyst bed. 

The heated secondary butyl alcohol (SBA) vapors are passed through a reactor containing zinc oxide catalyst at 750—1000°F at atmospheric pressure. The catalyst causes the hydrogen to pop off, forming MEK. The separation of the reactor effluent into MEK, water, hydrogen, and recycled SBA is about the same as Figure 17—2, The overall yield (the percent of SBA that ends up as MEK) is about 85-90%. 

Reaction with carbon monoxide using copper/zinc oxide catalyst yields methanol ... 

Fig. 3. Relation between frequency factors and heats of activation for the hydrogen-deuterium exchange reaction on zinc oxide catalysts (ref. 28a).

Fig. 4. Activation of zinc oxide catalysts in hydrogen -I- 2 % deuterium, flow rate 0.119 cc./sec. 215°C. A, X aSl C., O230°C.

Eucken (88,89) and Wicke (90) have tried to explain the dehydrogenation and dehydration of isopropyl alcohol by an electron interchange between the alcohol and the zinc oxide alumina catalysts used for these conversions. We shall modify the mechanism proposed by Eucken and Wicke, following the theory of chemisorption. Contrary to these authors, we do not believe that the positions of the zinc and oxygen ions on the surface of the zinc oxide catalysts have any appreciable influence upon... 

This alcohol can be reacted with methanol in the presence of a catalyst to produce methyl-r-butyl ether. Although it is currently cheaper to make Ao-butyl alcohol from Ao-butcne (Ao-butylene), it can be synthesized from syngas with alkali-promoted zinc oxide catalysts at temperatures above 400°C (750°F). 

Morpholine-2,5-dione and its substituted analogue, 6-methylmorpholine-2,5-dione, appeared to undergo copolymerisation with lactide in the presence of the zinc oxide catalyst. The copolymers obtained were characterised by an increased content of a-hydroxyacid units. The copolymerisability of the unsubstituted monomer was comparable with that of lactide. However, the N-methylated monomer was much less susceptible than the unsubstituted one to copolymerisation with lactide [178],... 

Bienholz A, Blume R, Knop-Gericke A, Giergsdies F, Behrens M, Claus P. Prevention of catalyst deactivation in the hydrogenolysis of glycerol by Ga203-modified copper/zinc oxide catalysts. J Phys Chem C. 2011 115 999-1005. 

Liu G, et al. The rate of methanol production on a copper-zinc oxide catalyst - the dependence on the feed composition. J Catal. 1984 90(l) 139-46. 

Kniep BL, et al. Rational design of nanostructured copper-zinc oxide catalysts for the steam reforming of methanol. Angew Chem Int Ed. 2004 43(1) 112 15. 

Gunter MM, et al. Redox behavior of copper oxide/zinc oxide catalysts in the steam reforming of methanol studied by in situ X-ray diffraction and absorption spectroscopy. J Catal. 2001 203(1) 133—49. 

Waller D, et al. Copper-zinc oxide catalysts. Activity in relation to precursor structure and morphology. Faraday Discuss Chem Soc. 1989 87 107-20. 

Whittle DM, et al. Co-precipitated copper zinc oxide catalysts for ambient temperature carbon monoxide oxidation effect of precipitate ageing on catalyst activity. Phys Chem Chem Phys. 2002 4(23) 5915-20. 

Quantitative and qualitative changes in chemisorption of the reactants in methanol synthesis occur as a consequence of the chemical and physical interactions of the components of the copper-zinc oxide binary catalysts. Parris and Klier (43) have found that irreversible chemisorption of carbon monoxide is induced in the copper-zinc oxide catalysts, while pure copper chemisorbs CO only reversibly and pure zinc oxide does not chemisorb this gas at all at ambient temperature. The CO chemisorption isotherms are shown in Fig. 12, and the variations of total CO adsorption at saturation and its irreversible portion with the Cu/ZnO ratio are displayed in Fig. 13. The irreversible portion was defined as one which could not be removed by 10 min pumping at 10"6 Torr at room temperature. The weakly adsorbed CO, given by the difference between the total and irreversible CO adsorption, correlated linearly with the amount of irreversibly chemisorbed oxygen, as demonstrated in Fig. 14. The most straightforward interpretation of this correlation is that both irreversible oxygen and reversible CO adsorb on the copper metal surface. The stoichiometry is approximately C0 0 = 1 2, a ratio obtained for pure copper, over the whole compositional range of the... 

Fig. 13. The dependence of the carbon monoxide saturation adsorption (total) and irreversible adsorption (irreversible) on the Cu/ZnO ratio in the binary copper-zinc oxide catalysts...

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... 

By far the most important synthesis gas reaction is its conversion into methanol, using copper/zinc oxide catalysts under relatively mild conditions (50 bar, 100-250°C). Methanol is further carbonylated to acetic acid (see Section 22-7), so that CH3C02H, methyl acetate, and acetic anhydride can all be made from simple CO and H2 feedstocks. Possible pathways to oxygenates in cobalt catalyzed reactions are shown in Fig. 22-6. 

As the nickel-containing catalysts used in the reforming reaction are sensitive to poisons, any sulfur compounds present in the hydrocarbon feedstock have to be removed by hydrodesulfurization, generally with a combination of cobalt - molybdenum and zinc oxide catalysts [413] - [415], (Eqs. 38, 39). In a few cases, especially with... 

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