Cobalt/alumina acidity

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

The conversion of CO to CO2 can be conducted in two different ways. In the first, gases leaving the gas scmbber are heated to 260°C and passed over a cobalt—molybdenum catalyst. These catalysts typically contain 3—4% cobalt(II) oxide [1307-96-6] CoO 13—15% molybdenum oxide [1313-27-5] MoO and 76—80% alumina, JSifDy and are offered as 3-mm extmsions, SV about 1000 h . On these catalysts any COS and CS2 are converted to H2S. Operating temperatures are 260—450°C. The gases leaving this shift converter are then scmbbed with a solvent as in the desulfurization step. After the first removal of the acid gases, a second shift step reduces the CO content in the gas to 0.25—0.4%, on a dry gas basis. The catalyst for this step is usually Cu—Zn, which may be protected by a layer of ZnO. 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

Partial seizure activity can be induced by the localised application of chemicals such as cobalt or alumina to the cortex or the injection of chemicals such as PTZ or kainic acid directly into particular brain areas like the hippocampus. 

Also, manganese added to cobalt on activated carbon catalysts resulted in a decrease in bulk carbide formation during reduction and a decrease in the subsequent deactivation rate.84 Magnesium and yttrium added to the support in alumina-supported cobalt catalysts showed a lower extent of carburization. This was explained by a decrease in Lewis acidity of the alumina surface in the presence of these ions.87... 

For the most highly developed processes, maf coal conversion can be as high as 90 to 95 % with a C4+ distillate yield of 60 to 75 wt % and a hydrogen consumption of 5 to 7 wt %. When an external catalyst is used, it is typically some combination of cobalt, nickel, and molybdenum on a solid acid support, such as silica alumina. In slurry hydrogenation processes, catalyst life is typically fairly short because of the large number of potential catalyst poisons present in the system. 

Metal molybdates421 and cobalt-thoria-kieselguhr422 also catalyze the formation of hydrocarbons. It is believed, however, that methanol is simply a source of synthesis gas via dissociation and the actual reaction leading to hydrocarbon formation is a Fischer-Tropsch reaction. Alumina is a selective dehydration catalyst, yielding dimethyl ether at 300-350°C, but small quantities of methane and C2 hydrocarbons423 424 are formed above 350°C. Heteropoly acids and salts exhibit high activity in the conversion of methanol and dimethyl ether.425-428 Acidity was found to determine activity,427 130 while hydrocarbon product distribution was affected by several experimental variables.428-432... 

OxideofOoba.lt, the ores of which, after grinding and roasting, to drive off as much as possible the excess of arsenic and sulphur, are dissolved in hydrochloric add, sometimes with the addition of a small quantity of nitric acid. The copper, lead, silver, arsenic, antimony, el cetera, are precipitated by sulphide of hydrogen, and to the filtered solution carbonate of lime is added in (he form of chalk, by which all the iron, alumina, and a trace ot cobalt are thrown down, the nickel and cobalt remaining in solution. To this solution which must ho hot and neutral, a solutien of bleaching powder is added in sufficient quantity to precipitate the cobalt, and the menstruum is then well boiled to remove the chlorine as fast as possible. The oxide of nickel is afterwards precipitated from the filtrate by the addition of hydrate of lime, and ebullition. 

Each c.c. of free space corresponds with 20 sq. cms. of catalyst surface. E. I. Orloff observed the oxidation of ammonia when mixed with air and passed over a heated copper gauze 4NH3-f-302 =2N2+6H20, with traces of nitrous and nitric acids—aniline, toluidine, and pyridine were oxidized in a similar way. W. W. Scott and W. D. Leech found that the conversion efficiency of cobalt oxide at 600°-800° is 79 3 per cent. This is augmented when about 3 per cent, of bismuth, or 10 to 12 per cent, of alumina, is used as... 

These experiments indicate that at low calcination temperatures the cobalt ions are present on the catalyst surface and neutralize the Brdnsted acid sites of the molybdate surface layer. At the higher calcination temperatures, the cobalt ions move into the alumina lattice. The BrGnsted acid sites reappear, indicating that the situation on the molybdate surface is restored. 

However, the molybdenum-alumina and the high calcined cobalt-molybdenum-alumina samples still show an important difference. The pyridine spectra of MoCo-124 indicate a second Lewis acid site, characterized by the 1612 cm-1 band. This band differs from the weak Lewis acid sites of the alumina support (1614 cm- ) because the position is significantly different. It also appears that the strength of the bond between pyridine and the catalyst is stronger, for the 1612 cm-1 band is still present after evacuation at 250°C, while the weak Lewis band (1614 cm-1) of the alumina has disappeared at this desorption temperature. Obviously the second Lewis band for the MoCo-124 catalyst is introduced by the interaction of cobalt with the surface molybdate layer. This interaction is... 

The molybdate surface layer in the molybdenum-alumina samples is characterized by the presence of BrGnsted acid sites ( 1545 cm- ) and one type of strong Lewis acid sites (1622 cm l). Cobalt or nickel ions are brought on this surface on impregnation of the promotor. The absence of BrtSnsted acid sites is observed for both cobalt and nickel impregnated catalysts, calcined at the lower temperatures (400-500°C). Also a second Lewis band is observed at 1612 cnrl.The reflection spectra of these catalysts indicate that no cobalt or nickel aluminate phase has been formed at these temperatures. This indicates that the cobalt and nickel ions are still present on the catalyst surface and neutralize the Brdnsted acid sites of the molybdate layer. These configurations will be called "cobalt molybdate" and "nickel molybdate" and are shown schematically in Figure 11a. 

For the high temperature calcined cobalt-molybdenum-alumina catalysts, the presence of a cobalt aluminate phase has been concluded from the reflection spectra. The BrtSnsted acid sites reappear in the spectrum of absorbed pyridine, indicating that the... 

The reappearance of Brdnsted acid sites has been observed for the high calcined nickel-molybdenum-alumina catalysts. The presence of a nickel aluminate phase has been concluded from the reflectance spectra. The second Lewis band (1612 cm l) has a very low intensity, in comparison with the cobalt containing catalysts of a same composition and after the same calcination conditions. 

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