Chromium oxide on alumina

It was later shown that aziridine reacts over mixtures of zinc and chromium oxides on alumina at 400°C to give the same products as those obtained from mixtures of NH3 and acetylene [221]. Aziridine, which would form by addition of NH3 to acetylene followed by IH (Scheme 4-8), was thus postulated to be an intermediate in the formation of acetonitrile (by dehydrogenation), monoethylamine (by hydrogenation) and all other heterocyclic bases (by ammonolysis and subsequent reactions) [221]. 

Several benzologs of furan and thiophene are conveniently formed by procedures of ring closure over dehydrogenation catalysts. o-Ethylphenol is cyclized at 620° over a palladium catalyst to benzofuran (11%). Chromium oxide on alumina at 450° converts o-ethylthiophenol to benzo-thiophene (42%). Alkyl groups in the alpha and beta positions are obtained by suitable variation of structure in the alkyl side chain. For the... 

The second peak in Figure 197 is a very-high-MW peak centered near 6.0 on the logarithmic MW scale (MW = 106 g mol-1). Because of its very high MW, and the low temperature used to calcine the alumina, this peak is probably the result of a di-attached Al-associated site. A similar peak, also assigned to an oxidic chromium species, was observed (Figure 194) by heat treatment of another diarenechromium(O) catalyst. The MW of that peak is consistent with the GPC of polymer made with chromium oxide on alumina. 

Dispersion of supported oxides can be studied by determining the effect of concentration on susceptibility at a single temperature. A susceptibility isotherm for chromium in chromium oxide on alumina at -188 C is shown as the top portion of Figure 2 ( 5). This isotherm shows a sharp decrease in susceptibility as the chromium concentration is increased to 9%. At higher concentrations, a smaller decrease in susceptibility with increasing concentration is observed. The susceptibilities for supported 2 3 does not attain the value for bulk Cr 0 which is about 30 X 10 at 188°C. 

The dealkylation of toluene and xylenes to benzene is carried out not only catalyt-ically but also as a purely thermal reaction in the presence of hydrogen. In the catalytic process, pressures ranges from 35 to 70 bar and temperatures from 550 to 650 °C chromium oxides on alumina are used as catalysts. Thermal dealkylation takes place at temperatures up to 750 °C and pressures of around 45 bar. 

The plant produces liquid hydrogen of a para concentration of 95 or better. Conversion of the normal hydrogen is accomplished in a number of steps in order to approximate continuous conversion during the cooling of the hydrogen gas. The catalyst used for conversion is the well-known chromium oxide on alumina. The liquid is produced under pressure, but in a subcooled condition, to facilitate transport from the plant to the storage tanks. 

Table IV. Polymerization over Nickel Oxide—Chromium Oxide on Silica—Alumina...

The first polymerizations were free radical reactions. In 1933 researchers at ICI discovered that ethene polymerizes into a branched structure that is now known as low density polyethene (LDPE). In the mid- 50s a series of patents were issued for new processes in which solid catalysts were used to produce polyethene at relatively low pressures. The first was granted to scientists at Standard Oil (Indiana) who applied nickel oxide on activated carbon and molybdenum oxide on alumina. Their research did not lead to commercial processes. In the late 40s Hogan and Banks of Phillips were assigned to study the di- and trimerization of lower olefins. The objective was to produce high octane motor fuels. When they tried a chromium salt as promoter of a certain catalyst (Cr was a known reforming... 

Styrene (phenylethene, 10) is an important industrial chemical that is prepared by dehydrogenation of ethylbenzene at 600 °C over zinc oxide or chromium(III) oxide on alumina (Scheme 3.7). Ethylbenzene can be produced from benzene and ethene by a Friedel-Crafts reaction. 

In 1964 a short investigation was made of EPR signals of platinum on alumina by F. Nozaki, D. Stamires and Turkevich.(70) The relation of catalytic activity of transition metal oxides to their EPR properties was studied. Thus in 1967 Kazanski investigated the chromium oxide on silica and its ability to carry out low temperature polymerization of ethylene. 

Chromium oxide catalysts on support polymerize isoprene-like butadiene to solid polymers. Here too, however, during the polymerization process, polymer particles cover the catalyst completely within a few hours from the start of the reaction and retard or stop further polymer formation. The polymerization conditions are the same as those used for butadiene. The reactions can be carried out over fixed bed catalysts containing 3% chromium oxide on Si02-Al203. Conditions are 88°C and 42 kg/cm pressure with the charge containing 20% of isoprene and 80% isobutane [122]. The mixed molybdenum-alumina catalyst with calcium hydride also yields polyisoprene. 

In the 1950s, almost two decades after the launch of LDPE, transition metal catalysts proved capable of producing unbranched linear low density polyethylene (LLDPE) and linear high-density polyethylene (HOPE), both of which had significantly different properties from LDPE. Remarkably, the discovery occuued nearly simultaneously in three different research groups using three different catalyst systems. First was Standard of Indiana s reduced molybdate on alumina catalyst in 1951, followed by Phillips with chromium oxide on silica ( chromox ) catalysts, and Ziegler s titanium chloride/ alkylaluminum halide systems in 1953 (only the latter two were widely commercialized). At about the same time, crystalline polypropylene (PP) was produced in the Phillips labs... 

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. ... 

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