Catalyst nickel/silica

Breeder etal. (Ill) have carried out S.P. and magnetization experiments to distinguish between ionic and covalent bonding for the adsorption of H2 and O2 on Ni. Nickel contains 9.4 electrons, 0.6 hole, and 0.6 unpaired electron spin per atom in the d band, the latter being responsible for the magnetic properties of the metal. The S.P. measurements were made on an evaporated Ni film and the magnetization studies on a nickel-silica catalyst, the properties of which were regarded as strictly comparable with the metal film. 

From the changes in magnetic susceptibility of nickel—silica catalysts during ethylene adsorption at room temperature, Selwood [55] has concluded that ethylene exists both as an associatively and a dissociatively adsorbed species. On increasing the temperature, the dissociative adsorption becomes more important. Thus at 100° C, the susceptibility changes are consistent with the formation of six bonds to the surface for each adsorbed ethylene molecule, suggesting the following process... 

II. Texture and Structure of Nickel-Silica Catalysts 1. Introduction... 

P4-22g Alkylated cyclohexanols are important intermediates in the fragrance and perfume industry [Jnd. Eng. Chem. Res., 28, 693 (1989)]. Recent work has focused on gas-phase catalyzed hydrogenation of o-cresol to 2-methylcyclo-hexanone, which is then hydrogenated to 2-methylcyclohexanol, In this problem we focus on only the first step in the reaction (Figure P4-22). The reaction on a nickel-silica catalyst was found to be zero-order in o-cresol and first-order in hydrogen with a specific reaction rate at 170°C of 1.74 mol of o-cresol/(kg cat - min - atm). The reaction mixture enters the packed-bed reactor at a total pressure of 5 atm. The molar feed consists of 67% Hj and 33% o-creso at a total molar rate of 40 mol/min. 

Metal-support interaction was observed in two nickel-silica catalysts, but they were prepared either by precipitating a complex carbonate from nickel nitrate solution containing Si02 as a slurry or co-precipitating the carbonate from a solution of nickel nitrate and sodium silicate. The similar spectra from the unreduced catalysts resembled in shape and binding energy a NiSi03 standard and were quite distinct from NiO. The interaction was... 

It was found originally by Swift and Bozik in an early study of supported bimetallic catalysts that the addition of tin to a nickel-silica catalyst greatly promoted the activity and gave a longer catalyst life for the dehydrogenation of cyclohexanol or cyclohexanone to phenol, especially with a... 

Transport may occur over the surface or through the atmosphere, with ihe latter most likely to involve molecular intermediates. This is true with platinum-alumina, for example, where oxidizing atmospheres during regeneration produce volatile PtO molecules. In nickel-silica catalysts exposed to carbon monoxide, nickel carbonyl serves the same purpose. For surface transport, atomic migration is favored, but depends on the substrate composition. 

P. W. Selwood (Northwestern University) Now that Professor de Boer has mentioned the subject, I want to state my belief that the nickel surfaces in a typical reduced nickel-silica catalyst are no less free from surface contamination than those ordinarily obtained by the thin-film technique. From this statement I exclude those surfaces carefully prepared by Professor Farnsworth s argon-ion bombardment method. 

B. Nickel-Silica Catalyst It was prepared by impregnating wet silica gel with nickel nitrate solution, drying the mass, and decomposing the nitrate to the oxide at 350-400°. It was subsequently reduced in a stream of hydrogen at 300-350°. 

Nitta, Y., Kawabe, M., Sun, L., Ohmachi, Y., and Imanaka, T. (1989) Preparation of uniformly dispersed Nickel-silica catalysts from S5mthetic Nickel-Chrysotile, Appl Catal. 53, 1 -28. 

Figure 7.5 Effect of silicate addition temperature on pore size in nickel/silica catalyst made by sequential precipitation [21].

Preparation of highly loaded nickel/silica catalysts by a deposition-precipitation metood. Effect of the aging time on the reducibility of nickel and on the textural properties of the catalyst. 

A particular issue is the deactivation of methanation catalysts by carbon formation. Kuijpers et al. [345] observed significant carbon formation over a nickel/kieselgur catalyst containing 54wt.% nickel when exposed to a mixture of 10 vol.% carbon monoxide, 15 wt.% hydrogen, with a balance of nitrogen at 0.6 bar pressure and a 250 °C reaction temperature. Carbon filaments were found, which contributed to 10 wt.% of the catalyst mass at the inlet of the fixed bed. A nickel/silica catalyst showed practically no coke formation for 1000 h duration under the same conditions. 

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