Copper-on-alumina catalysts

Without doubt, copper deposited on high surface area aluminas constitute an important class of catalysts for many of the above reactions. Because of the widespread importance of deactivation in such a variety of catalytic systems, the study of deactivation of copper on alumina catalysts using a classical oxidation-reduction reaction, such as carbon monoxide oxidation, may provide fundamental background for the elucidation of aspects of the more complex reactions. 

Consequently, the present work has focused to the structural changes accompanying deactivation of copper on alumina catalyst employed for CO oxidation, showing also the effect of the presence of copper-chromite phase on such deactivation. 

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. 

Oxychlorination Process to produce vinyl chloride monomer from ethylene, hydrogen chloride, and oxygen over a copper chloride on alumina catalyst. 

In the traditional plant concept, the gas from the secondary reformer, cooled by recovering the waste heat for raising and superheating steam, enters the high-temperature shift (HTS) reactor loaded with an iron - chromium catalyst at 320 - 350 °C. After a temperature increase of around 50 - 70 °C (depending on initial CO concentration) and with a residual CO content of around 3 % the gas is then cooled to 200-210 °C for the low-temperature shift (LTS), which is carried out on a copper - zinc - alumina catalyst in a downstream reaction vessel and achieves a carbon monoxide concentration of 0.1-0.3 vol%. 

Cyclododecanol is dehydrogenated to cydododecanone around 200°C, in the liquid phase, in the presence of a catalyst consisting of copper on alumina. For a 75 per cent conversion, cydododecanol selectivity is 98 molar per cent The reactor effluent is first rid of the hydrogen formed by flash and fractionated in two successive light-ends and heavy-ends separation columns (7 kPa absolute, 25 to 30 trays each). 

Figure 2 shows the behavior of the activity with time on stream of low (5wt%) and high (30wt%) metal concentration Cu and Cu-Cr catalysts. At low metal concentrations, it can be seen that copper catalyst is affected by a pronounced deactivation whereas the Cu-Cr catalyst is not. Accordingly, it can be suggested that active copper sites in CuCr O are less prone to deactivation, i.e., more stable, than active copper on alumina. In the case of the high con-... 

A cobalt-impregnated, copper-zinc oxide on alumina catalyst has been reported for the carbonylation of ethanol to ethyl acetate (74). A catalyst comprising CuO-ZnO-Al20s impregnated with Co(NOs)2 was found to be more active toward formation of ethyl acetate from ethanol and carbon monoxide, in comparison with an analogous catalyst in the absence of Co. The use of Re was also reported. 

Even the industrial copper/zinc/alumina-based catalysts have been modified to achieve higher productivity or longer catalyst life. ICI recently announced its third-generation copper/zinc/alumina catalyst, described as a "step change" over the previous catalysts [16, 17]. This development was made through optimized formulation and particle and pellet size. Researchers at the University of New South Wales, Australia claimed another new breakthrou on this type of the catalyst [16]. A 100% improvement in performance over the previous catalysts was claimed. 

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). 

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Dutch State Mines (Stamicarbon). Vapor-phase, catalytic hydrogenation of phenol to cyclohexanone over palladium on alumina, Hcensed by Stamicarbon, the engineering subsidiary of DSM, gives a 95% yield at high conversion plus an additional 3% by dehydrogenation of coproduct cyclohexanol over a copper catalyst. Cyclohexane oxidation, an alternative route to cyclohexanone, is used in the United States and in Asia by DSM. A cyclohexane vapor-cloud explosion occurred in 1975 at a co-owned DSM plant in Flixborough, UK (12) the plant was rebuilt but later closed. In addition to the conventional Raschig process for hydroxylamine, DSM has developed a hydroxylamine phosphate—oxime (HPO) process for cyclohexanone oxime no by-product ammonium sulfate is produced. Catalytic ammonia oxidation is followed by absorption of NO in a buffered aqueous phosphoric acid... 

In a typical oxychlorination reaction, preheated gas streams at temperatures of 180—200°C are fed onto a fixed- or fiuidized-catalyst bed containing 2—10% copper impregnated on an activated alumina. The reaction occurs during a 15—22 s residence time on the catalyst bed at a temperature of 230—315°C. Typical yields to 1,2-dichloroethane range from 92—97%. 

Ethylamines. Mono-, di-, and triethylamines, produced by catalytic reaction of ethanol with ammonia (330), are a significant outlet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, siUca, or sihca—alumina. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethylamine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give W-ethylpiperidine [766-09-6] (332). 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

Park PW, Ledford JS (1998) The influence of surface structure on the catalytic activity of cerium promoted copper oxide catalysts on alumina oxidation of carbon monoxide and methane. Catal Lett 50(1—2) 41 48... 

In situ dynamic surface structural changes of catalyst particles in response to variations in gas environments were examined by ETEM by Gai et al. (78,97). In studies of copper catalysts on alumina, which are of interest for the water gas shift reaction, bulk diffusion of metal particles through the support in oxygen atmospheres was shown (78). The discovery of this new catalyst diffusion process required a radical revision of the understanding of regeneration processes in catalysis. 

Copper high Miller index, 26 12 Copper oxide, 27 184-187, 199 as adsorbent, 21 44 on alumina, 27 80-85 -manganese oxide, 27 91, 92 oxidation of CO over, 24 86 -platinum catalyst, 27 86-88 propylene oxidation, 30 141 Coprecipitation, perovskite preparation, 36 247-250... 

The following examples describe in situ studies of copper metal catalysts supported on alumina in different gas environments. 

A similar oxidation-reduction mechanism in the carbon monoxide oxidation reaction on oxide catalysts has been proposed by Benton (71), Bray (72), Frazer (73), and Schwab (74). In this reaction also, Mooi and Selwood (57) found that a decrease in the percentage of iron oxide, manganese oxide or copper oxide on the alumina support first increased the rate, and then at lower percentages decreased the rate, of carbon monoxide oxidation, indicating that valence stabilization is again operative in these cases. 

Copper chloride is universally applied as catalyst. - Known as the modified Deacon catalyst, CuCl2 is supported on alumina and contains KC1. Under operating conditions a CUCI2-CU2CI2-KCI ternary mixture, possibly in the molten state, is... 

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