Activated adsorption of hydrogen on nickel catalysts

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Abstract
The chemisorption of hydrogen on a Ni‐catalyst obtained by coprecipitation from Ni(NO3)2, Na2CO3‐ and Na silicate solutions at 80° C and containing Ni and SiO2 in the ratio 3 Ni‐1 SiO2 was investigated.In agreement with other investigations it was found that the adsorption consists of a very rapid process followed by a much slower one, the latter increasing in velocity with increasing temperature. The transition between the two is not sharp but gradual. However, some distinction may be made by observing the amounts of hydrogen adsorbed at liquid nitrogen temperatures and very low pressure (type I) and the amounts which can be adsorbed in excess of this quantity (type II).It was found that a more thorough reduction of the catalyst resulted in an increase of the type I adsorption at the cost of type II. Adsorption of oxygen on a well‐reduced catalyst on the contrary decreased the type I and increased the type II adsorption, the change being linear with the amount of oxygen adsorbed. Oxygen adsorption can occur in two different manners. It is assumed that depending on the conditons one adsorption site can be occupied by either an oxygen atom or an oxygen molecule.Heating of a reduced catalyst in an inert atmosphere or under vacuum tends to eliminate the type I adsorption while also the total adsorption diminishes. It is suggested here that a reoxidation of the surface occurs (combined with some sintering). Two causes for this reoxydation are considered: diffusion of oxygen in the interior of the metal—metaloxide structure to the surface liberation of water vapour by the silica carrier followed by the reaction Ni + H2O → NiO + H2.

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