CATALYSIS: THE GUIDE OF LIFE 113 



excess of hemin to displacement of linoleic acid molecules from the 

 interfacial film. They conclude that orientation of substrate and 

 hemin molecules in the interfacial film is of decisive importance for 

 the establishment of the catalysis. This is, of course, true, and it 

 involves the electronic contour factor (1) mentioned above; but the 

 kinetic factor (2) is also to be reckoned with. 



How Catalysts are Modified 



The technological and patent literature has long reflected the 

 fact that the introduction of new atoms or molecules into the 

 active surface of a catalyst may stimulate, inhibit, or alter the 

 nature and/or rate of the catalyzed reaction. 28 If a desired result 

 is accelerated, the added substance is termed a promotor; if it is 

 inhibited, the added substance is called an inhibitor or poison. 

 In cases where a catalyst can direct the formation of several sub- 

 stances and an inhibitor is found which depresses undesired reac- 

 tions, we speak of "beneficial poisoning." In a general sense any 

 substance which changes the behavior of a catalyst may be called 

 a modifier, a term free from implication as to the result of the 

 change. The importance of catalyst modification in biology will 

 be referred to later on. 



One factor in the efficiency of a catalyst is the amount of free 

 active surface it exposes to the reactants. It is common commer- 

 cial practice to distribute the catalyst substance on carriers, or 

 supports, such as asbestos, charcoal, alumina, diatomaceous earth 

 (kieselguhr), etc., which are supposed to act merely mechanically. 

 It has been found, however, that the carrier often exercises a 

 marked effect, either by contributing small amounts of impurities 

 to the catalyst surface (which may thus be either promoted or 

 poisoned), or else by forming with the catalyst molecules some 

 new composite surface of different activity. 29 



According to recently released information 30 a substantial 

 amount of the synthetic rubber produced during the recent war 

 was made from ethyl alcohol by the Lebedev process. An effi- 

 ciency of about 65 per cent in butadiene synthesis was obtained 

 with a silica gel catalyst promoted by tantalum oxide, and nearly 

 as good results were had with the more plentiful zirconium oxide 

 as promotor. 



The potent effect of catalyst poisons is brought out by the remarks 

 of H. Bernthsen at the Eighth International Congress of Applied Chem- 



