[ERPS] more thoughts on catalysts

[Pierce Nichols]

In order to get my thinking on the subject straight, I called my chem consultant (my sister, currently getting a PhD in biology). First, the decomposition reaction is a redox reaction or something similar, which means that, in general, it's the metal oxides doing the catalyzation. My intuition on the subject was correct; now I have some clue as to why. Second, the temperature is only relevant to the catalytic activity to the degree that it affects the oxidation state of the base metal. This may explain why some potential catalysts, such as platinum, show so little activity at room temperature -- they simply are not sufficiently oxidized. Third, catalytic activity occurs when the peroxide molecule gets 'stuck' to the catalyst surface, reacts with the catalyst to form an intermediate, and then goes through a second reaction to form the products. In this set of reactions, peroxide is serving as the electron donor (reducing agent), and the catalyst is serving as an electron acceptor (oxidizing agent). The energy released in this reaction is proportional the difference in the electron potentials between the donor and acceptor. Since peroxide has a very high electron potential (i.e it's eager to donate), we need to find a metal oxide with a highly negative electron potential (i.e. it's eager to accept). This gives us a search criteria that's easy to work with -- the relevant tables are in the front of the Handbook of Chemistry & Physics. The bigger the difference, the more violent the reaction.

-p


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