Nickel on silica

The reaction scheme is rather complex also in the case of the oxidation of o-xylene (41a, 87a), of the oxidative dehydrogenation of n-butenes over bismuth-molybdenum catalyst (87b), or of ethylbenzene on aluminum oxide catalysts (87c), in the hydrogenolysis of glucose (87d) over Ni-kieselguhr or of n-butane on a nickel on silica catalyst (87e), and in the hydrogenation of succinimide in isopropyl alcohol on Ni-Al2Oa catalyst (87f) or of acetophenone on Rh-Al203 catalyst (87g). Decomposition of n-and sec-butyl acetates on synthetic zeolites accompanied by the isomerization of the formed butenes has also been the subject of a kinetic study (87h). 

Ramesh S, Yuri K, Ruslan P, Aharon G (1997) Sonochemical deposition and characterisation of nanophasic amorphous nickel on silica microspheres. Chem Mater 9 546-551... 

Data have been obtained for the rate of the heterogeneous reaction with catalyst of nickel on silica at 191 C (Yates et al, JACS 86 2996,1964) ... 

Catalyst 5% nickel on silica-alumina Pressure 350 lb./sq. inch gage Liquid space velocity 1.0 vol./vol./hour H2 HC, mole ratio 4.0... 

The metal-catalysed hydrogenation of cyclopropane has been extensively studied. Although the reaction was first reported in 1907 [242], it was not until some 50 years later that the first kinetic studies were reported by Bond et al. [26,243—245] who used pumice-supported nickel, rhodium, palladium, iridium and platinum, by Hayes and Taylor [246] who used K20-promoted iron catalysts, and by Benson and Kwan [247] who used nickel on silica—alumina. From these studies, it was concluded that the behaviour of cyclopropane was intermediate between that of alkenes and alkanes. With iron and nickel catalysts, the initial rate law is... 

Nickel on Silica-Alumina Catalyst, J. Phys. Chem. (1966) 70, 3666. 

Unlike most studies performed on one single reactor type, Turek et al [43] compared 4 reactors STR, TBR, spinning basket reactor, piston recycling reactor, with different nickel on silica particle sizes (glucose hydrogenation). See also [44]. 

Other approaches to the problem of the structure of nickel-on-silica catalysts revealed, however, that the above suggestions are only a first step to the truth. 

Hydrogenation of sesame seed oil with a nickel-on-silica catalyst 23... 

The reduction of nitriles is of wide scope and has been applied to many nitriles. When catalytic hydrogenation is used, secondary amines, (RCH2)2NH, are often side products.These can be avoided by adding a compound, such as acetic anhydride, which removes the primary amine as soon as it is formed, or by the use of excess ammonia to drive the equilibria backward. Sponge nickel or nickel on silica gel have been used for the catalytic hydrogenation of aryl nitriles to amines. 

Kosmulski, M., The effect of the ionic strength on the adsorption isotherms of nickel on silica, J. Colloid Interf. Sci., 190, 212, 1997. 

Example 10-4 Coenan has reported rates of hydrogenation of sesame seed oil with a nickel-on-silica catalyst in a slurry reactor. Hydrogen was added at the bottom of a small cylindrical vessel equipped with stator and stirrer blades. Initial rates of reaction were measured as function of catalyst concentration at 180°C, a stirrer speed of 75G rpm, atmospheric pressure, and a hydrogen rate of 60 liters/hr. The data, converted to global rates in terms of g moles/(min)(cm oil), are given in Table 10-6 (based on an oil density of 0.9 g/cm ). Estimate kiaJH from these data. Comment on the importance of the resistance of hydrogen to solution in the oil and estimate what the reaction rate would be if this resistance could be eliminated for a catalyst concentration of 0.07% Ni in oil. 

FifMre 8.8. CrystalNie size distribution changes Tor crystallite migration of nickel on silica at... 

Product distributions from the hydrocracking of typical normal paraffins with nickel sulfide on silica alumina catalyst (34, 59) are shown in Figure 1 (n-hexadecane) and Table I (n-decane). Table I also includes results with silica-alumina and with nickel on silica-alumina (discussed later). 

Weakly Acidic Supports. With unsulfided metals on acidic supports, isomerization is an important reaction. For example, Ciapetta and Hunter (12, 13, 14) demonstrated the effectiveness of nickel on silica-alumina and cobalt on silica-alumina for isomerization of n-paraffins. 

Here, we demonstrate the potential of ordered mesoporous materials as model supports by presenting results using SBA-15 as support. By employing SBA-15 we were able to identify the most detrimental step during the preparation of nickel on silica catalysts using nickel nitrate as precursor salt. Moreover, it is shown that these findings correspond with results obtained with a conventional silica gel support. 

XRD results of the reduced nickel on silica gel (G/SD-C-R) and SBA-15 (S/SD-C-R) samples reveal that metallic nickel was present with average crystallite sizes of 17 and 12 nm, respectively. STEM analysis of these samples (not depicted) show that the broad particle size distribution that was present prior to reduction has been hardly affected. Nickel particles with sizes ranging from 10 to 35 nm were observed for sample G/SD-C-R. No detailed information could be obtained for this sample regarding the distribution of the nickel particles over the support. Sample S/SD-C-R contained large nickel particles ( 25 nm) situated at the exterior surface as well as smaller nickel particles ( 7 nm) located inside the mesopores that appear to have made these pores (partially) inaccessible. Furthermore, the STEM images indicate that the distribution of the nickel particles over the support corresponded to that of the nickel oxide particles present before reduction. Nitrogen physisorption results demonstrate that still 80% of the mesopore volume was blocked by the nickel particles. Furthermore, the surface area and porosity had slightly increased upon reduction. 

Finally, we can conclude that by avoiding the detrimental calcination treatment in air highly dispersed nickel on silica catalysts at high loadings can be obtained. Therefore, reduction of dried nickel nitrate hydroxide is advocated to obtain highly dispersed catalysts. 

P. M. Gundry (BuckneU University) In connection with the relative merits of nickel films and nickel-on-silica catalysts in presenting a clean surface, I ould like to draw attention to a remark made by Professor Muller in a comment to Dr. Cunningham s paper. He said that he had observed in the emission microscope that glass was freely mobile on a tungsten surface at 400°. It is not possible that some of the silica of the... 

The hydroisomerization reaction is not only of industrial importance but is also of theoretical interest. The catalysts reported for this reaction consist of a hydrogenation component, such as nickel, platinmn, etc, deposited on acidic supports, such as silica-alumina ) or platinum on alumina containing halogen 2). A detailed study of the hydroisomerization reaction as a function of catalyst composition and experimental conditions has been reported ). Ciapetta (3a) studied the hydroisomerization of ethylcyclohexane over nickel on silica-alumina catalyst and reported that isomerization was the primary reaction and that the isomers consisted of dimethylcyclohexanes and of trimethylcyclopentanes. The dimethylcyclo-hexanes were stated to be composed of the 1,1- and 1,2-dimethylcyclo-hexanes, the latter predominating, and possibly of small amounts of 1,3-and 1,4-dimethylcyclohexanes. 

The state-of-the-art technology in free fatty acid hydrogenation is characterized by discontinuous operation and the use of powdered nickel on silica catalysts. Known disadvantages of this process are discontinuous operation, low... 

In contrast to these findings, earlier VH4 studies (34, 35] of the mcthylation of benzene and some other hydrocarbons with methane over nickel on silica and alumina catalysts showed that the methyl group was largely derived from sources other than methane gas. Carbonaceous species were thought to supply part of the carbon for mcthylation. A more recent CHi isotopic tracer investigation by Lunsford and co-workers [18] also failed to reveal the presence of any detectable C in the methylated products of the mcthylation of benzene over H-beta catalyst in a flow reactor at 400 X and 4.8 MPa pressure. The workers [18] then concluded that benzene served as the sole source of carbon in all of the observed products under their reaction conditions. Thus, it appears that there is tack of agreement in the... 

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