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Catalysts are things you can add to a reaction that provide an alternate reaction pathway for the reaction that decreases the overall activation energy of the reaction meaning the reaction is faster but the catalyst isn't consumed in the reactions. Are there any materials, in any reactions where a similar material can be added to a reaction that will decrease the rate of reaction by providing a more favorable reaction pathway but one that takes longer.

Maybe it isn't possible for a reaction to be more favorable but require a higher activation energy and this is why this kind of "pseudo catalyst" doesn't exist.

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    $\begingroup$ We'd probably call such a catalyst an inhibitor, and it probably work by increasing the activation energy instead of decreasing it. Perhaps a mutated enzyme could work, one that still binds its substrate with high affinity, but was not capable of catalysis. $\endgroup$
    – user137
    Commented Oct 29, 2020 at 14:54
  • $\begingroup$ In an electrochemical cell setting, one can accelerate the electrochemistry by increasing the surface area of the cathode relative to the anode. It follows that modifying the cell with inert material (less anodic than the current anode and less noble than the existing cathode) that decreases the surface area of the cathode could be an inhibitor. For example, create a partial CuO layer on an existing Cu cathode (aka, poison the cathode). $\endgroup$
    – AJKOER
    Commented Oct 31, 2020 at 9:37
  • $\begingroup$ Well, strictly speaking, a catalyst can only be a catalyst if it lowers the barrier as that is part of its definition. $\endgroup$
    – Martin - マーチン ♦
    Commented Oct 31, 2020 at 9:50
  • $\begingroup$ @AJKOER Certainly, but how do you do that? $\endgroup$
    – Karl
    Commented Oct 31, 2020 at 10:46
  • $\begingroup$ The poisoning of 'catalyst' occurs frequently with a vehicle's catalytic converter. In my reference to a Cu cathode, just remove part of it, wash and heated it in air till its glows red (Cu->Cu2O->CuO) inducing a visible alteration in color. Replaces the part and the battery cell performance changes. $\endgroup$
    – AJKOER
    Commented Oct 31, 2020 at 11:00

2 Answers 2

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Well, such a "negative catalyst" cannot increase the activation energy of already existing path.

An alternative with the higher activation energy would not be significantly taken. You can detour a river making it flow easier by a side channel, but not if you lead it across a hill.

It could act differently, as an inhibitor, blocking the low activation energy path by reaction with the key intermediate product or existing catalyst, or by competitive inhibition.

Many redox reactions, including food deterioration, are catalyzed by traces of transient metals acting as redox catalysts, typically copper. An additive, forming metal complexes like EDTA, in large extend inhibits these catalyzed reactions.

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  • $\begingroup$ With a pipe, if the hill is less than ten meters? Sorry. ;-) $\endgroup$
    – Karl
    Commented Oct 29, 2020 at 21:27
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    $\begingroup$ @Karl You would need to suck water up to this 10 m first. BTW, is it still a hill, according to English cartographic terminology ? $\endgroup$
    – Poutnik
    Commented Oct 29, 2020 at 21:57
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Possibly. Let's say your reaction is

$$\ce{D -> E}$$

Your inhibitor could catalyse an additional reaction

$$\ce{C <<=> D}$$

If the equillibrium of that reaction was well on the left side, that would slow down the original reaction quite a bit.

Alternatively, it could catalyse a reaction $\ce{D->B}$, where B had an additional pathway

$$\ce{E <- B <- D -> E}$$

, which might be slow.

This is all however very hypothetical. I cannot name an example for either.

Generally, if you find that something acts as an inhibitor, that means the reaction was already catalysed, and your inhibitor either permanently poisons the catalyst, or reversibly converts it into an inactive form.

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    $\begingroup$ Equilibrium arrows are <=>. <-> are for tautomerization/resonance. $\endgroup$
    – Poutnik
    Commented Oct 30, 2020 at 5:04
  • $\begingroup$ @Poutnik And you can even give them a bias <<=> <=>>. +1 $\endgroup$
    – Karl
    Commented Oct 30, 2020 at 18:41
  • $\begingroup$ sure, I use it often. See mhchem $\endgroup$
    – Poutnik
    Commented Oct 30, 2020 at 19:02
  • $\begingroup$ Karl: +1, your answer seems to incorporate my example of cathodic poisoning in a battery cell (cited in my comment above). $\endgroup$
    – AJKOER
    Commented Oct 31, 2020 at 9:45

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