Abstract
A detailed study of the kinetics of the heterogeneous catalytic
ortho
-
para
-hydrogen conversion on the solid free radical
αα
-diphenyl-
β
-picryl hydrazyl, shows that this conversion follows the usual first-order kinetics and that the rate is independent of pressure. Examination of the rate at 90, 190 and 290° K indicates that it decreases with increasing temperature. This type of behaviour has been observed for other paramagnetic heterogeneous conversions, and the ‘negative activation energy' has been assumed to indicate that the catalysis takes place in a physically adsorbed layer of hydrogen molecules. Some evidence that this is the true explanation of the phenomenon is shown by the results of studies of the adsorption of hydrogen on the free radical. Experiments carried out at 77 and 90° K indicate that hydrogen is physically adsorbed by the free radical to form a weakly sorbed layer which obeys the Langmuir adsorption isotherm for the case when the surface is only sparsely covered. A theoretical discussion is given for a heterogeneous conversion occurring during the collision of the hydrogen molecule with the catalyst surface both in the absence, and in the presence, of a physically adsorbed layer. It is shown that only the theory based on the latter model is in agreement with experimental results, and so it is concluded that in the present case the catalysis is due to the interaction between the hydrogen molecules in a physically adsorbed layer, and the inhomogeneous magnetic field at the surface of the catalyst, which enables the otherwise forbidden
ortho
-
para
transitions to take place.
Reference13 articles.
1. Bonhoeffer K . F . Farkas A. & R um m el K . W . 1933 phys. B 21 225.
2. Bonhoeffer K. F . & Harteck P . 1929 z - PhVs - Chem. B 4 113.
3. Trans;Faraday Soc.,1940
4. Advanc;Catalys.,1948
5. Farkas A. & Melville H . W . 1939 Experimental methods in gas reactions. L on d on : M acmillan and Co. Ltd.
Cited by
51 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献