We investigated decomposition of an organic compound in the supercritical water medium in both catalytic and non-catalytic situations ( the catalyst was iron oxide nanoparticle) and when it came to calculation of activation energy, we observe a strange effect. The activation energy was higher for catalytic reaction compared with non-catalytic one. How is it possible?
(As we know) However, there are lots of reactions and there is not a specific reaction happening in the medium. Would it be possible that in the presence of catalyst, some products such as active oxygen was produced and led to initiate a bunch of other reactions, which did not happen in the absence of catalyst? Can we attribute this increasing in the activation energy to a " reaction bulk", which differs for catalytic and non-catalytic situations?
Please, clarify what is "decomposition of an organic compound." Do you mean oxidation by O2?
Nano materials are more active than their bulk state, Your Nano-catalyst may have been poisoned by O2.
To Yurii V Geletii
Thank you for your answer.
Yes, I meant the decomposition of tributhyl phosphate at supercritical water oxidation, which is a medium approximately enrich of active oxygen required for oxidative decomposition.
My main concern is still remained unsolved in my mind how is it possible that activation energy for catalytic reaction is higher than its noncatalytic one?
Possible explanations:
1) the catalyst isn't functioning as a catalyst, but instead as some type of inhibitor
2) the catalyzed and uncatalyzed processes are different reactions or proceed by a significantly different mechanism
Not sure that this is helpful but it's what came to mind.
Good luck
I recommended Tom' s explanation. Just some minor comment.
In oxidation by O2 transition metals might become inhibitors under certain conditions.
"the catalyzed and uncatalyzed processes are different reactions (YES) or (and always) proceed by a significantly different mechanism
You probably determined the activation energy as a slope of Log(rate) versus 1/T. While you missed that the rate also depends on pre-exponential factor (activation entropy). The activation entropy is higher for the catalytic pathway. Plot "Log(rate) versus 1/T" dependences for both catalyzed and non-catalyzed reactions. They should cross each other at some temperature.
To Dear Professors Yurii V Geletii and Tom Mulhern
Thank you for your cordial support.
I am really appreciative. Your answers were really helpful and useful.
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