Alumina ethylene hydrogenation

A selective poison is one that binds to the catalyst surface in such a way that it blocks the catalytic sites for one kind of reaction but not those for another. Selective poisons are used to control the selectivity of a catalyst. For example, nickel catalysts supported on alumina are used for selective removal of acetjiene impurities in olefin streams (58). The catalyst is treated with a continuous feed stream containing sulfur to poison it to an exacdy controlled degree that does not affect the activity for conversion of acetylene to ethylene but does poison the activity for ethylene hydrogenation to ethane. Thus the acetylene is removed and the valuable olefin is not converted. 

The co-existence of at least two modes of ethylene adsorption has been clearly demonstrated in studies of 14C-ethylene adsorption on nickel films [62] and various alumina- and silica-supported metals [53,63—65] at ambient temperature and above. When 14C-ethylene is adsorbed on to alumina-supported palladium, platinum, ruthenium, rhodium, nickel and iridium catalysts [63], it is observed that only a fraction of the initially adsorbed ethylene can be removed by molecular exchange with non-radioactive ethylene, by evacuation or during the subsequent hydrogenation of ethylene—hydrogen mixtures (Fig. 6). While the adsorptive capacity of the catalysts decreases in the order Ni > Rh > Ru > Ir > Pt > Pd, the percentage of the initially adsorbed ethylene retained by the surface which was the same for each of the processes, decreased in the order... 

Ethylene stoichiometrically reacts with Pd(CN)2 in benzonitrile at 150 °C to give acrylonitrile in 55% yield. This reaction can be performed catalytically by reacting ethylene, hydrogen cyanide and oxygen at 350 °C over PdCl2/V205/CsCl supported on alumina. The selectivity in acrylonitrile is about 90%, and the productivity about 20 g/g Pd/hour (equation 185).379... 

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

Recent studies by Maret et al. have investigated the process of spillover activation of amorphous alumina (135,136). If the sample was cooled in H2 from 430 to 180°C with the source of spillover present (supported Pt), no induction period was found for ethylene hydrogenation. This implies that... 

For reactions that are the same on metal and other catalytic sites (e.g., hydrogenation or total oxidation), the reaction may seem to proceed in a similar fashion on the metallic source of spillover and on the diluent support. Some careful studies may be able to discriminate between activity on the metal and the spillover-induced sites. As an example, hydrogenation of ethylene occurs on Pt (or Ni) and on silica or alumina activated by spillover. The product (i.e., only ethane) is the same, as the kinetics often are (rate = /c[C2H4]°[H2]1), but the specific mechanism is different. Deuteration is able to discriminate between the relative rate of alkyl reversal. Deuteration of ethylene on an activated silica produces d2-ethane as the initial product (137), contrary to the results for metal-catalyzed ethylene hydrogenation (2). 

K R. Prairie and J, Bailey Experimental and modelling investigations steady - state and dynamic characteristics of ethylene hydrogenation Pt/alumina Chem. Engng. Sci, A2 (1987) 20B5 - 2102. 

Beebe TP Jr, Yates JT Jr (1986) An in situ infrared spectroscopic investigation of the role of eth-yhdyne in the ethylene hydrogenation reaction on palladium/alumina. J Am Chem Soc 108 663... 

Experiments performed in a flow reactor system showed some very unexpected results for the deposition of carbon from the decomposition of ethylene/hydrogen (1 1) mixtures on alumina supported cobalt particles. It was found that the amount of carbon deposited over the temperature range 400 to 700°C was dependent on the time of the reduction step optimum yields being obtained following an 18 hr treatment in hydrogen. 

Ethylene hydrogenation over a Pt catalyst supported on y-alumina catalyst has been extensively investigated. Somoijai and Carazza... 

Catalysis of Ethylene Hydrogenation and Hydrogen-Deuterium Exchange by Dehydrated Alumina... 

These results seemed to be inconsistent with any simple electronic theory of hydrogenation catalysis they were, however, relevant to the general concept that dehydration of oxide catalysts should leave the surface in a strained, catalytically active condition ( , S). A systematic study was therefore undertaken of the activation of pure y-alumina for ethylene hydrogenation and hydrogen-deuterium exchange the effects of pretreatment, drying conditions, and rehydration were investigated. 

The alumina-supported cluster [Al]+[HRuOs3(CO)i3] was catalytically active for 1-butene isomerization. After catalysis, [Al]+[H3RuOs3(CO)i2] was the only detectable metal carbonyl species. This supported catalyst decomposed during ethylene hydrogenation at 340 K to give catalytically active metal particles. 

In addition to the differences in catalytic activity, there are other fundamental differences between the two catalysts. With alumina, surface hydrogen participates both in the adsorption (on sites II) and in the polymerization of ethylene. With silica-alumina this is not the case, at least not in the adsorption of ethylene. Related results have been obtained by Ozaki and Kimura 22) who have recently studied the isomerization of w-butenes on deuterated acid catalysts and in the presence of deuteropropylene on nondeuterated acid catalysts. In the initial stages of the reaction scarcely any deuterium was found in the reactant butene on silica-alumina while it appeared extensively in the reactant and the product on alumina. 

Figure 23 shows the TPD chromatograms of ethylene on alumina after hydrogenation at room temperature at various pressures of hydrogen (Phs) experiments ethylene was initially adsorbed on both... 

In connection with ethylene hydrogenation, adsorption of hydrogen on alumina has also been studied by the TPD technique. Some of the... 

The foregoing observations narrow down the likely mechanism of ethylene hydrogenation on alumina and provide another example of the potential usefulness of the TPD technique. However, once again, further work will be required before aU the important aspects of the reaction mechanism are clarified. 

Carter and coworkers in 1965 (32) examined alumina using infrared spectroscopy as the surface catalyzed ethylene hydrogenation reaction. By knowing the number of molecules in the system, the rate, and the total number adsorbed on active and inactive sites, they were able to conclude that one possible explanation of their results was that the site density was very low. 

PS Acetophenone, benzophenone, enones, diketones, phenylacetaldehyde, sucdnimides, benzoyl peroxide, in chain peroxide linkages, hydroperoxides, polycyclic aromatic hydrocarbons, Fe derivatives, Co salts of fatty acids, AICI3, silica-alumina catalyst Hydrogen, benzene, conjugated double bonds, methane, ethylene, radicals, crosslinks Water, CO2, ketones, unsaturations, hydrtperoxides, radicals, chain scissions, quinomethane structures... 

Nickel oxide/chromium oxide supported on alumina. Selective hydrogenation in ethylene and hydrogen mixtures. 

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