Zinc-copper catalyst

Li JL, Inui T. Characterization of precursors of methanol synthesis catalysts, copper zinc aluminum oxides, precipitated at different pHs and temperatures. Appl Catal A Gen. 1996 137(1) 105 17. 

Optimized catalysts (copper/zinc oxide) can reduce the process conditions to 50-100 bar and 250 °C. Methanol will then be burned as fuel in combustion engines or in fuel cells, according to [227]... 

In the 1960s, a new catalyst revolutionized the production of methanol, which had been made by the BASF high pressure or zinc oxide-chromia catalyst process since 1923. The new catalyst—copper, zinc oxide, and chromia or other oxide— had been known as a methanol catalyst for a considerable length of time. At ICI, researchers carried out a careful and systematic program of preparing and testing mixed catalyst systems. The new process operated under much milder conditions than the old one. Pressure was reduced from 200 to 50-100 atm and temperature dropped from 350 to 250°C. Virtually all methanol plants built after 1967 employed this technology (69). 

Isobutyl alcohol [78-83-1] forms a substantial fraction of the butanols produced by higher alcohol synthesis over modified copper—zinc oxide-based catalysts. Conceivably, separation of this alcohol and dehydration affords an alternative route to isobutjiene [115-11 -7] for methyl /-butyl ether [1624-04-4] (MTBE) production. MTBE is a rapidly growing constituent of reformulated gasoline, but its growth is likely to be limited by available suppHes of isobutylene. Thus higher alcohol synthesis provides a process capable of supplying all of the raw materials required for manufacture of this key fuel oxygenate (24) (see Ethers). 

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. ... 

Because the synthesis reactions are exothermic with a net decrease in molar volume, equiUbrium conversions of the carbon oxides to methanol by reactions 1 and 2 are favored by high pressure and low temperature, as shown for the indicated reformed natural gas composition in Figure 1. The mechanism of methanol synthesis on the copper—zinc—alumina catalyst was elucidated as recentiy as 1990 (7). For a pure H2—CO mixture, carbon monoxide is adsorbed on the copper surface where it is hydrogenated to methanol. When CO2 is added to the reacting mixture, the copper surface becomes partially covered by adsorbed oxygen by the reaction C02 CO + O (ads). This results in a change in mechanism where CO reacts with the adsorbed oxygen to form CO2, which becomes the primary source of carbon for methanol. 

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). 

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). 

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 U.S. Department of Energy has funded a research program to develop the Hquid-phase methanol process (LPMEOH) (33). This process utilizes a catalyst such as copper—zinc oxide suspended in a hydrocarbon oil. The Hquid phase is used as a heat-transfer medium and allows the reaction to be conducted at higher conversions than conventional reactor designs. In addition, the use of the LPMEOH process allows the use of a coal-derived, CO-rich synthesis gas. Typical reactor conditions for this process are 3.5—6.3 MPa (35—60 atm) and 473—563 K (see Methanol). 

The catalyst is a mixture of copper, zinc oxide, and chromium(lll) oxide. Ethanol is produced in large quantities throughout the world by the fermentation of carbohydrates. It is also prepared by the hydration of ethene in an addition reaction ... 

Microanalysis of a Copper-Zinc Oxide Methanol Synthesis Catalyst Precursor... 

Himelfarb, P. B., Simmons, G. W., Klier, K., Herman, R. G., "Precursors of the Copper-Zinc Oxide Methanol Synthesis Catalysts," J. Catal., in press. 

Present catalysts are developed for process plant service where transient conditions are not a concern. Typical shift catalysts, such as copper-zinc oxide, are reduced in place and must be isolated from air. There is a need for smaller, high surface area catalyst beads on low-density monolith substrate to be developed without reducing activity. This need applies to all fuel processor catalyst, not just the shift catalysts. There is also a need to demonstrate that the low-temperature, PROX catalysts have high selectivity toward CO and long term stability under operating conditions. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

With the same excess of catalysts hydrogenations of the esters over Raney nickel could be carried out at temperatures as low as 25-125° at 350atm with comparable results (80% yields). However, benzene rings were saturated under these conditions [55]. In addition to nickel and copper, zinc and chromium oxides, rhenium obtained by reduction of rhenium heptoxide also catalyzes hydrogenation of esters to alcohols at 150-250° and 167-340 atm in 35-100% yields [42]. 

Adjustment of the C0 H2 ratio is effected by the shift reaction (iv) which proceeds over a chromium-promoted iron catalyst at 700-800°F (370-425°C) or over a reduced copper/zinc catalyst at 375" 50°F (190-230 C) and the fraction of crude gas sent through the shift reactor is calculated from the initial gas composition and specific downstream requirements. The latter are i1 lustrated by... 

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

Manganese can also be a catalyst. Manganese [as Mn(III)] in superoxide dismutase from Thermus thermophilus (Stallings et al., 1984, 1985) is surrounded by three histidines, one aspartate oxygen, and water in a trigonal bipyramidal arrangement. The fifth coordination site is occupied by a water molecule. In copper, zinc-superoxide dismutase (Cu,Zn = SOD), as described later, there are two metals (copper and zinc). Each bonds to and are separated by this same histidine group. 

Synthesis from Citronellol. Citronellol is hydrated to 3,7-dimethyloctan-l,7-diol, for example, by reaction with 60% sulfuric acid. The diol is dehydrogenated catalytically in the vapor phase at low pressure to highly pure hydroxydihydrocitronellal in excellent yield. The process is carried out in the presence of, for example, a copper-zinc catalyst [68] at atmospheric pressure noble metal catalysts can also be used [69]. 

Among the characterized metal homoenolates, only zinc homoenolate of alkyl propionate undergoes substitution reactions with electrophiles under suitable conditions. Two types of metal catalysts, copper(I) and metals of the nickel triad (e.g. Pd), have successfully been used to effect allylation, arylation, and vinylation reactions. 

The low-pressure methanol synthesis process utilizes ternary catalysts based on copper, zinc oxide, and another oxide, such as alumina or chromia, prepared by coprecipitation. Cu-Zn0-Al203 and Cu-Zn0-Cr203 are usually the most important industrial catalysts. A significant advance was made when a two-stage precipitation was suggested in which ZnAl2C>4, a crystalline zinc aluminate spinel, was prepared prior to the main precipitation of copper-zinc species.372 This alteration resulted in an increase in catalyst stability for long-term performance with respect to deactivation. Catalyst lifetimes industrially are typically about 2 years. 

One process (182) esterifies the acetic acid with ethanol (or methanol) and then converts the ester to alcohol by hydrogenolysis in the vapor phase over a copper—zinc catalyst. 

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