I quote the Wikipedia page definition for Turnover number:

In other chemical fields, such as organometallic catalysis, turnover number (abbreviated TON) has a different meaning: the number of moles of substrate that a mole of catalyst can convert before becoming inactivated. An ideal catalyst would have an infinite turnover number in this sense, because it wouldn't ever be consumed, but in actual practice one often sees turnover numbers which go from 100 up to 40 million for catalase.

I'm trying to find reasons for why catalysts don't function infinitely in practice. My only thoughts are that maybe they eventually degrade from slowly reacting with other species they are exposed to, but then wouldn't this depend on the environment it is in rather than how much substrate it catalyses? I also assume that all product is taken away as it is produced.

  • 4
    $\begingroup$ Because they are not ideal. They may get inactivated by the substrate itself (say, 1 time in a 100), or by certain impurities in the substrate (so-called catalytic poisons). $\endgroup$ – Ivan Neretin Feb 8 '16 at 22:25
  • $\begingroup$ @IvanNeretin How does a catalyst become inactivated by its substrate? $\endgroup$ – k-- Feb 8 '16 at 22:35
  • 1
    $\begingroup$ @IvanNeretin means that some real catalysts can undergo more than one reaction with a substrate. It may only occur rarely (1/100 in his example) but that 1/100 reactions is enough to inactivate a molecule of real catalyst. $\endgroup$ – Jason Patterson Feb 8 '16 at 22:46
  • 1
    $\begingroup$ @k-- Say, every once in a while our reaction takes a wrong turn, and the product (the wrong one) gets permanently stuck to the catalyst, rendering it inactive. $\endgroup$ – Ivan Neretin Feb 8 '16 at 22:47
  • $\begingroup$ @repurposer oops yeah I meant turnover number $\endgroup$ – k-- Feb 9 '16 at 3:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.