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An apparatus for the investigation of the effect of poisonous substances, and mixed vapours on catalytic activity

Published online by Cambridge University Press:  24 October 2008

F. H. Constable
F. H. Constable
Affiliation:
Strathcona Research Student, St John's College.
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Extract

(1) An apparatus has been devised in which the composition of the vapour phase passing over the catalyst can be varied at will, or two vapours can be used alternately as reactants.

(2) By using ethyl alcohol, and amyl alcohol from fusel oil alternately as reactants, the poisoning of a very active copper gauze catalyst has been followed and the temperature coefficient of the dehydrogenation of ethyl alcohol by the copper has been measured during the poisoning.

(3) The activity of the catalyst, poisoned by amyl alcohol, fell in accordance with the simple logarithmic law

(4) Confirmation was obtained that the rates of dehydrogenation of ethyl and amyl alcohols were equal.

(5) The temperature coefficient of dehydrogenation on the catalyst was unchanged throughout the poisoning, though the reaction velocity was reduced 30 times.

(6) The temperature coefficient was also shown to be unchanged during sintering, the reaction-velocity having been reduced 10 times.

(7) Equations are derived for the rate of poisoning of an exponential distribution of centres of activity when the poison attacks the more active centres selectively.

(8) The relation deduced

cannot usually be distinguished (except with special relations between the constants) from the simple logarithmic law of poisoning.

(9) Thus the exponential distribution normally poisons like a surface composed of homogeneous centres, the temperature coefficient being unchanged by the poisoning.

(10) The equation

describes the reaction-velocity as a function of time, and temperature, and gives adequate explanation of previous experimental results on the forms of the heating and cooling curves with “poisonous” alcohols.

(11) Frenkel has shown , where τ0 is the vibration frequency of the molecule perpendicular to the surface, and μ0 is the heat of desorption of one gram molecule. Thus if the heat of desorption is not small compared with the energy necessary to cause chemical disruption of the molecule, the previous equation becomes

the form of the equation being unaltered.

Type
Research Article
Information
Mathematical Proceedings of the Cambridge Philosophical Society , Volume 22 , Issue 5 , July 1925 , pp. 738 - 750
Copyright
Copyright © Cambridge Philosophical Society 1925

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References

* Palmer, and Constable, , Proc. Roy. Soc. ‘A,’ vol. 106, p. 251 et seq.CrossRefGoogle Scholar

* When ethyl alcohol and a copper catalyst were being used one limb contained chromic acid on pumice, and the other (nearest the burette) damp soda-lime.

* The reactions catalysed by the copper are

(1)

(2) which falls off with time owing to poison-ing due to traces of impurity in the amyl alcohol.

* Constable, , Proc. Roy. Soc. ‘A,’ vol. 108, p. 374. “On the Mechanism of Catalytic Decomposition.”Google Scholar

* See Palmer, and Constable, , Proc. Soy. Soc. ‘A,’ vol. 107, p. 263.Google Scholar

* See Taylor, H. S., J. Phys. Chem. vol. 28, p. 911. (1924.)Google Scholar

† I.e. kt must be considerably less than | h − 1/RT | hence does not vary much daring the poisoning. See “Mechanism of Catalytic Decomposition” loc. cit.

* Proc. Roy. Soc. ‘A,’ vol. 107, p. 258, Fig. 1.Google Scholar