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How do catalysts work ?


vrus
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I wanted to know how catalysts work. My teachesr just said that it lowers the activation energy of a reaction, so that the bonds are looser, and according to the simple collision theory, molecules are able to have more successful collisions. All this is well, but a little more detail as to how the activation energy is lowered would be helpful. Is there any formula based method or any other that can identify a catalyst for a reaction, or do you haver to find out by trial and error?

 

I am under the impression that catalysation has something to do with the catalyst's surface area. If so, for example in the case of the catalytic breakdown of Hydrogen Peroxide, say manganese dioxide is the catalyst, how does the reaction get faster, if the catalyst is settled at the bottom?

 

I'd greatly appreciate any help, as if a strange thought or idea arises in my mind, I find it hard to work on topics relating to that...

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There you go :

 

X+Y => XY without cat.

 

X+Y+K => (X+K)aktivated condition +Y => XK+Ytemporary condition

XK+Y=> (XK+Y)aktivated condition => XY+K

 

The cat. makes some kind of temporary compound which is combined wid a lower energy that is needed to built it.Then the direct reaction of X and Y.

The compound XK reacts immediately under less activation energy with Y.

 

The temporary compound can be a real chemical compound.

 

By the way manganese dioxide reacts with hydrogen peroxide (redox-reaction)

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Catalysis is a very complex subject. Usually, there is no formula to determine whether a substance can catalyze a certain reaction. To find a catalyst for a certain reaction you would usually search through the literature to see what catalysts are available for your reaction. If one wants to design a new catalyst for a reaction, it is generally a trial-and-error process although one can usually try to base the design off of existing catalysts (one such method is designing simplified analogues of enzyme active sites).

 

Catalyst is also a very broad term. A catalyst could be something as simple as an inorganic acid to something as complicated as (R,R)-(-)-N,N'-bis(3,4-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese (III) chloride or even biological enzymes (which are much more complicated).

 

The activity of a catalyst does not necessarily depend on its surface area. This is true only of heterogenous catalysts, or catalysts which are in a different phase than the reactants (for example, solid MnO2 in aqueous hydrogen peroxide or solid Pt with gaseous carbon monoxide and nitrogen oxides). However, the activity of homogenous catalysts will depend on their concentration (for example, in the case of biological enzymes see Michaelis-Menten Kinetics).

 

A catalysts' mechanism of action is dependent on the catalyst itself. Not all catalysts work in the same way, so all you can only really say that catalysts lower the activation energy of a reaction. One must examine how the catalyst lowers the activation on a case-by-case basis.

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well, as yggdrasil said, there are many types of catalysts, but one example is in the formation of NH3 from N2 and H2. The catalyst used is platinum and rhodium. The catalyst in this instance causes the N2 and H2 to bind to it, weakening the bonds in each molecule. This either lowers the energy required to separate individual atoms or separates them entirely. The highly reactive H and N atoms are then form NH3 which leaves the catalyst.

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well, as yggdrasil said, there are many types of catalysts, but one example is in the formation of NH3 from N2 and H2. The catalyst used is platinum and rhodium. The catalyst in this instance causes the N2 and H2 to bind to it, weakening the bonds in each molecule. This either lowers the energy required to separate individual atoms or separates them entirely. The highly reactive H and N atoms are then form NH3 which leaves the catalyst.

 

 

That's not quite right.You need in many reactions precious metals to adsorb the H2 on their surface , but in this reaction (haber-bosch-synthese) you need a ironoxide-cat. (Fe2O3 mixed up with some other Oxides like Al2O3 ,CaO etc.)

 

Just to get you right :D

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  • 4 years later...
  • 3 weeks later...
how do catalyst works in organic reactions?


Merged post follows:

Consecutive posts merged

how do catalyst works in organic reactions?:)

 

Hi, I think the other posts did a very good job of explaining how a catalyst works and you can easily apply that to organic reactions.

 

Hopefully I'm understanding you correctly, but I think you might be asking if catalysts behave differently in organic reactions? If that is your question then it can't be generalized in this way. Catalysts are typically very specific for a certain type of reaction like there are specific catalysts for things like Suzuki couplings (a named reaction in organic chemistry) and there are catalysts for polymerization reactions (like Ziegler Natta). Both of those catalysts are different and cannot be compared in the method I believe you might be hoping to compare all catalysts. I guess a good way to demonstrate this would be to say that you cannot use the palladium catalyst in the suzuki reaction to do the polymerization reaction that requires the Ziegler Natta, they are almost never interchangeable. A lot of extremely hard work and research goes into designing reaction specific catalysts as result. Someone can have an entire career working on catalysts for one specific type of reaction. :)

 

Sorry I couldn't be of more help.

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Catalysts work upon activation, and the activation comes when you connect the carbons or atoms to each other. Think of water and sand, they are interactive, yes?

 

Now if you were to have a catalyst where you take gold and silver, for example, you would find that there is no reaction, but resistance. The resistance - no not the Frenchies in the war - would be where they fail to catlise or whatever, meaning that they would resist occupying the same area. If there is resistance, and not 'fusion', then there will be no reaction, but rather rejection of bonding - they are not soluble, interactive, or, in simple English, they will not mix.

 

I hope you can agree with me, or, tell me where I am wrong...

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  • 1 year later...

I wanted to know how catalysts work. My teachesr just said that it lowers the activation energy of a reaction, so that the bonds are looser, and according to the simple collision theory, molecules are able to have more successful collisions. All this is well, but a little more detail as to how the activation energy is lowered would be helpful. Is there any formula based method or any other that can identify a catalyst for a reaction, or do you haver to find out by trial and error?

 

I am under the impression that catalysation has something to do with the catalyst's surface area. If so, for example in the case of the catalytic breakdown of Hydrogen Peroxide, say manganese dioxide is the catalyst, how does the reaction get faster, if the catalyst is settled at the bottom?

 

I'd greatly appreciate any help, as if a strange thought or idea arises in my mind, I find it hard to work on topics relating to that...

 

What isaction through inaction :

 

 

The concept of the Catalyst :The concept of Enablement :

 

 

Let usstudy the example of Hydrogen Peroxide : What happens with and without theCatalyst – Manganese Dioxide

 

 

HydrogenPeroxide is a reasonably stable chemical : on its own, the decomposition ofhydrogen peroxide is so slow that hydrogen peroxide solutions are commerciallyavailable.

 

 

Upon theaddition of a small amount of manganese dioxide, the hydrogen peroxide reacts rapidly.

 

 

This effect isreadily seen by the effervescence of oxygen. Or simply put, release of Oxygen.

 

 

The manganesedioxide is not consumed in the reaction, and thus may be recovered unchanged,and re-used indefinitely.

 

 

Modern Scienceis yet to understand the Physics of the Chemical Reaction that Catalysts enable.

 

 

It seems to befalling in the twilight zone : between science and religion. Or you can say, inthe Zone where Science and Religion meet. The zone of will. Of wantingsomething to happen. In the above example, Manganese Dioxide, persuades - HydrogenPeroxide to let go of the Oxygen that it has within it.

 

 

The use of theterm persuade is important – because it is not giving anything that physicsrecognizes – energy of any kind – chemical, kinetic or of any other kind.Sometimes it is said that it is providing a surface where the reaction can takeplace. But this is difficult to sustain – because surface can be provided bymany many substances - it is only the surface provided by this particularcatalyst ( in this case Manganese Dioxide ) that is acceptable as a surface bythe chemical.

 

 

In other words,when molecules of the chemical meet when they are sticking on to the catalyst,they behave differently, than when they are not sticking to the catalyst.

 

 

In the statewhen they are sticking to the catalyst, they seem to become different than whothey are when they are not sticking to it. Now what is it that they have, or donot have, when they are sticking to the catalyst. Physically speaking, there isnothing that they have or do not have – as defined by sub-atomic particles.What they have is something beyond physics.

 

 

To my mind, whatthe molecules have is something beyond matter – is knowledge.

 

 

In homeopathicmedicine, this knowledge is enhanced through multitude of meetings between theknowable substance and a ready to learn – neutral- substance ( Alchohol, orwater). As the dilutions increase- the potency increases. Each dilution meansanother set of meetings between the neutral substance and the knowledgeablesubstance – through the process of constant shaking of the mixture.

 

 

Thereupon theknowledge stays with the Neutral substance permanently. And is available forfurther transmission to the human intellect system to produce the desiredresponse from the body.

 

 

So there is aScience here, though it is not explainable under the laws of Physics as weunderstand it.

 

 

There is adifferent science which covers this knowledge – as per Mundaka Upanishad, it is called Para Vidya – as distinct from Apara whichcovers everything that is material – and is covered by modern science.

 

 

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!

Moderator Note

RBS, this is a mainstream chemistry forum, and it must follow mainstream chemistry theories.
Opinions about what "knowledge" molecules have "beyond" "matter" is not mainstream science. If you want, you can open a thread in our Speculation forum and convince us of your speculative theory.

Do not post this in the mainstream thread.

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Rubbish.

 

Catalysis of many different reactions is already understood without evoking anthropomorphic molecules. I hope you're prepared to argue for a while about this one.

 

We don't get many chemistry speculations around here. I've been waiting for you...welcome. Begin by presenting some evidence of your outlandish assertions.

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  • 3 weeks later...

It's a double reaction:

 

the first one, the caralyst is no longer there and it's elements are in the product

 

the second one, the products containing the elements of the catalyst react again and the catalyst is back, intact.

 

 

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