Nickel-chromia catalyst

Chemical exchange between hydrogen and steam (catalyzed by nickel—chromia, platinum, or supported nickel catalysts) has served as a pre-enrichment step in an electrolytic separation plant (10,70). If the exchange could be operated as a dual-temperature process, it very likely... 

Thus, in the first place, by means of the combined thermochemical and comparative methods one obtains values for bond energies of hj drogen, carbon, and oxygen with nickel (Table XI) very similar to those found when using the first variant of the kinetic method for chromia (Table XII). At the same time, as the chemical compositions of nickel and chromia catalysts are different these values do not coincide, which is consistent with the theory. 

A less detailed model led Wheeler [1955] to a value of 2. Wakao and Smith [1962] obtained values between 2.5 and 3.5 for macro-micro pore networks. Feng and Stewart [1973] and also Dullien [1975] obtained a value of 3 for perfectly interconnecting pores with completely random orientation. Experimental values reported by Feng and Stewart [1973] for alumina pellets are 4.6 by Dumez and Froment [1976] for a chromia/alumina catalyst, 5 by De Deken et al. [1982] for a Ni/AhOs steam reforming catalyst, 4.4 to 5.0 by Satterfield and Caddie [1968], from 2.8 to 7.3 and by Patel and Butt [1974] from 4 to 7 for a nickel/molbydate catalyst. Note that the above calculation does not account for dead end pores and that the pores are considered to be strictly... 

Nickel. As a methanation catalyst, nickel is presently preeminent. It is relatively cheap, it is very active, and it is the most selective to methane of all the metals. Its main drawback is that it is easily poisoned by sulfur, a fault common to all the known active methanation catalysts. The nickel content of commercial nickel catalysts is 25-77 wt %. Nickel is dispersed on a high-surface-area, refractory support such as alumina or kieselguhr. Some supports inhibit the formation of carbon by Reaction 4. Chromia-supported nickel has been studied by Czechoslovakian and Russian investigators. 

Carbonates, diaryl, reactions with cyclohepta-amylose, 23 240 Carbon dioxide adsorption, 21 44 on chromia, 20 27 on gallium-doped NiO, 22 247-251 on nickel catalysts, 22 87-96 dissociative, 22 93-96... 

G-41 A chromia-alumina catalyst, used for hydrodealkylation and dehydrogenation reactions G-S8 Palladium-on-alumina catalyst, for selective hydrogenation of acetylene in ethylene G-52 Approximately 33 wt % nickel cm a refractory oxide support, prereduced. Used for oxygen removal from hydrogen and inert gas streams... 

In the discussion of the subject Balandin mentions (15) that Fischer previously postulated that methylene radicals may be produced as an intermediate in the formation of hydrocarbons by his method (116). This mechanism of carbon deposition on platinum supported on oxides of nickel and chromium (oxidized nichrome) through the intermediate formation of methylenes was thought by Balandin to be similar to the mechanism of dehydrogenation over this type of catalyst in that both occur on the boundaries of platinum-nickel and of platinum-chromia and were brought in agreement by him with his multiplet theory (26). 

Two illustrative examples will be discussed. The first example, the chromia-promoted iron oxide catalysis of the water-gas shift reaction, can be solved to engineering accuracy on a hand calculator. The second example, steam reforming of methane over a supported nickel catalyst, involves multiple... 

Other transition M(II) dopants do not produce promotional effect to match that of Zn(II), although nickel(II) nor Mg(II) doped catalysts have characteristics in common with the Zn(II) analogues. These results are in accordance with other studies of Ni(II) [88] and Mg(II) [89] as dopants for chromia. Although lightly doped Mg(II) chromias had inferior conversion of CF3CH2C1, these catalysts had longer lifetimes than chromias which were undoped. 

XPS and TEM measurements indicate that after fluorination, zinc and nickel, on the surface of these catalysts is present as ZnF2 or NiF2, respectively and these findings support the idea that the Zn(II) and Ni(II) species on doped fluorinated chromias do not become integrated into the surface structure but are, in fact, distinct phases on the surface. 

After a preliminary study of the properties of a number of platinum and nickel catalysts deposited on various carriers (activated carbon, chromia, alumina, molybdena, etc.) a platinum-alumina catalyst was selected for the present investigation with a 0.5 % Pt content. Cyclopentane (238.2 g) was passed over the catalyst at 0.43 hr. i space velocity, 20 atmospheres hydrogen pressure, and a temperature of 460 . As a result 184.3 grams of liquid product were obtained containing 9 % by volume of aromatics including benzene (81.9%), toluene, and p-xylene, and also w-pentane,... 

Comparison of catalytic activities for samples containing different percentages of nickel was done by the method which had previously proved convenient for testing the dehydrocydization of n-heptane over chromia-alumina. In all activity tests the total nickel concentration was set at 3.33 per cent nickel. In all but the most dilute sample this was achieved by making a mechanical dilution of the original prepared catalyst. The diluting i ent was y-alumina identical with that used for impregnation. 

Apart from the degree of reduction affecting overall performance, the nature of the support is also crucial in determining final activity. For supported molyb-dena catalyst, alumina and titania support materials provide best performance. Silica, zirconia, chromia, and zinc oxide are also good support materials, although they produce less active catalysts. Inactive catalysts can be readily synthesized by supporting molybdena upon cobalt oxide, nickel oxide, magnesium oxide, or tin oxide. To date, no correlation between the acidity of the support material and cataljdic activity has been found (304). 

In addition, Raman spectroscopy also provides structural information about the presence of small metal oxide crystallites and surface reaction intermediates. Several extensive reviews of supported metal oxide catalysts have recently appeared in the literature, which have emphasized Raman spectroscopy vanadia [7,83-85], chromia [7,85,86], molybdena [7,87], niobia [7,88], rhenia [7,85], tungsten oxide [7], titania [85], and nickel oxide [89]. 

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