Chemistry. — ''Heterogeneous catalysis and the orientation of adsorbed 

 molecules". By Prof. H. R. Kruyt and C. F. van Duin, 



(Communicated at the meeting of September 30, 1922). 



In a previous communication^) we published investigations on the 

 relation between liie adsorbtion of reacting substances an the velocity 

 of the reaction, with the object of coming to a better understanding 

 of heterogeneous catalysis. In ttiese investigations we found, that by 

 giving coal to the reacting system a decrease of the velocity sets 

 in, even in cases, where undoubtedly an increase of the reacting 

 components in the surface layer takes place. 



In accordance with the theory of I. Langmuir') and W. D. Harkins^) 

 concerning the special condition of molecules, which are situated in 

 surface layers, we tried to explain our results by the assumption 

 1. that adsorbed molecules have partly lost their mobility and con- 

 sequently a great deal of the possibility of meeting and reacting 

 with other molecules, and 2. that adsorbtion can cause positive 

 catalysis only in the case, when the molecules are adsorbed in such 

 a way that the number of effective collissions increases. 



That adsorbtion in itself can have a decreasing ejffect was found 

 when studying a monoraolecular reaction, viz. the transformation of 

 racemic dibromo-succinnic acid into bromo fumaric acid and HBr"), 

 The results are given in ihe tables 1 and II. 



Evidently a marked decrease in the velocity occurs. 



We discussed in the paper cited above, that a positive contact 

 catalysis can be expected only in the case, when the reacting group 

 is turned away from the adsorbent and towards the surrounding 

 liquid. With charcoal as an adsorbent, and water as milieu, all 

 electrically polar groups will be turned towards the water; we 

 therefore had chosen the reaction of «/? dibromo-propionic acid and 

 KJ (formation of acrylic acid, KBr and J,). As might have been 



1) Rec. trav. chim. Pays Bas 40, 249 (1921). 

 ') Journ. amer. chem Soc. 39, 354 en 541 (1917). 

 S) Journ. amer. chem. Soc. 38, 2221 (1916) and 39, 1848 (1917). 

 *) Gf. HoLMBERG, Journ. f. prakt. Ghem. 84, 145 (1911) and Zeitschr. f. physik. 

 Chem. 79, 147 (1912). 



