[boswell] catalysis OF HYDROGENATION BY NICKEL 15 



OH- 



+ H2O 



Reaction (1) represents the main reaction M^hich occurs. It 

 expresses the mechanism of hydrogénation by an active nickel cata- 

 lyser. 



Reaction (2) represents the slow removal of negative hydroxyls 

 from the surface of the catalyser and the adsorption of hydrogen 

 constantly taking place. 



Reaction (3) represents the slow reaction of this adsorbed hydro- 

 gen with the unchanged nickel oxide in the interior of the particles. 



A fourth reaction also occurs, involving the addition of positive 

 and negative hydrogens from neutral hydrogen molecules to the com- 

 plex on the right hand side of reaction (1), to form the complex on 

 the left hand side of reaction (3). This fourth reaction represents 

 the mechanism of hydrogen adsorbtion. 



Equations (2) and (3) also represent the reactions which occur on 

 continued reduction of nickel oxide by hydrogen. This continues 

 until all the nickel oxide in the interior of the particles has been 

 reduced and until finally all the hydroxyls on the surface have been 

 removed and only adsorbed hydrogen, as positive hydrogens and 

 negative hydrogens, remains. Thus the hydrogen which is taken 

 up in excess of the equivalent of water formed is held on the surface 

 in two ways: (1) as positive hydrogens and negative hydroxyls, and 

 (2) as positive hydrogens and negative hydrogens. 



Evidently the water represented in these equations is not all 

 evolved for if such were the case the catalyser would soon lose all 

 its oxygen and, as will shortly be pointed out, lose almost entirely its 

 capacity for catalysing hydrogénations. This water is only evolved 

 in the free state in relatively small amount, the chief part remaining 

 on the particles as hydrogens and hydroxyls. This is equivalent to 

 saying that in reaction (1) a negative hydroxyl on the surface of the 

 catalyser has a tendency to unite with a positive hydrogen of a 

 neutral hydrogen molecule, thus loosening the bond between the 

 positive and negative hydrogens of the hydrogen molecule sufficiently 

 to permit the positive and negative hydrogens of the hydrogen mole- 

 cule to unite with a molecule of ethylene. That is the hydrogénation 

 is pictured as occurring primarily at the surface of the particles by 

 means of oscillating hydrogen atoms which are at one instant more 

 closely associated with the hydroxyls and hydrogens- on the surface 



