Nickel catalysts magnetization-temperature

Fig. 11. Changes in specific magnetization of a supported nickel catalyst during adsorption and desorption of hydrogen at room temperature. [Selwood, P. W., J. Am. Chem. Soc. 78. 3893 (1956).]...

Table I summarizes the characteristics of nickel catalysts prepared onto these supports. For brevity these catalysts will be referred to by a notation in the form aA-fi. For example, 7AAP-573 represents a 7 wt % Ni catalyst supported on A O 2A1P0 reduced at 573 K for 1 h. Incidentally, this sample did not reduce under these conditions and was excluded from further kinetic studies. Notations for the other catalysts are shown in the first column of Table I. All samples were reduced at the specified temperature for 1 h unless noted otherwise. The percent reduction was determined by measuring oxygen uptake at 673 K in a commercial thermogravimetric system (Cahn 113). The average particle size was determined by either X-ray diffraction line broadening or magnetic measurements (see below).

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... 

In this respect, magnetic measurements give valuable information. They can show whether poisons react not only with surface metal atoms but also with subsurface atoms as for the case of H2S chemisorption over Nt/Si02 catalysts (refs. 11. 12) the loss of magnetization caused by H2S chemisorption at saturation at room temperature is twice that produced by H2 chemisorption at atmospheric pressure and room temperature in a separate experiment. Assuming that hydrogen chemisorption is restricted to surface metal atoms, then, it can be deduced that H2S is able to attack the nickel particle in depth (corrosive chemisorption). 

Commercially, cobalt is used primarily in high-temperature alloys, in tungsten carbide tools, and (with iron and nickel) in permanent magnets. Cobalt salts are used in pigments, in paint dryers, and as catalysts in the petroleum industry. 

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