Talk:Catalyst

Defined

The definition in my chemistry class is "Substances that alter the rate of a reaction without being consumed by the reaction." I think it is also important to stress that they sometimes slow down reactions. The biology misconception is that ALL catalysts SPEED up reactions. This has been mentioned before and is very misleading.

Chris C.

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Compare the definition of catalyst, which refers only to accelerating a chemical reaction, to the Wikipedia definition of enzyme, which refers to "facilitate or otherwise accelerate." I think it is important to emphasize in both definitions that the catalyst/enzyme enables interactions that under normal circumstances would not take place without it. I think one mischaracterizes the fundamental concept of a catalyst/enzyme to refer to it only as an accelerant. A catalyst/enzyme is fundamentally an "interface" that enables interactions between diverse components, be they chemicals, proteins, ideas, etc.

-- Nick Gall

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What is meant by "an active part"? In most cases the catalyst does react chemically with one or more of the reactants to form an intermediate (possibly an adsorbed species). Subsequently, the intermediate reacts to give the desired product and the catalyst, thus regenerating the catalyst. Since the catalyst is actually participating in the reactions, I would say that it does play an active part, but it is regenerated in subsequent reactions. --Matt Stoker

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Exactly. In my original definition, I said something to the effect that a catalyst participates, but is otherwise unconsumed.

I guess that was too concise for whomever decided to add the more verbose, and incorrect, text. -- dja

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"net" is probably fine. I was thinking "overall" might be more precise, but I'm not sure.

--Matt Stoker

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Also, I've been wondering to what extent reaction mechanisms should be discussed in this entry, or in Kinetics, or . . . somewhere else? I think some of our struggles with the description of a catalyst center around the difference between the bulk view of reactions versus a molecular understanding of those reactions. In the bulk sense, they are unconsumed. In the microscopic (ie, microscopic reversability) sense, they are consumed and regenerated. This is close to, but not quite fully, a semantic distinction.

Thoughts?

--dja

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Personally, I think a simple generic reaction mechanism (as is currently in the page) is appropriate at least for the initial general discussion. More detailed discussions of reaction mechanisms would probably fit nicely in Kinetics, especially if someone could take the time to demonstrate how some important kinetic equations (eg. Eleay-Rideal and Langmuir-Hinshelwood type equations) result from elementary reactions.

One additional thought I have been pondering is whether it would be appropriate to give some examples of important industrial catalysts and catalytic processes. Would this be more appropriate under Catalyst or Catalysis, also what level of detail is appropriate?

--Matt Stoker (sorry I omitted this label initially)

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In keeping with the spirit of wiki and wikipedia as I see it, as much detail as you can pump out is encouraged. Put it out there, and if necessary, it can be refactored later.

The concern I have about where to focus on reaction mechanisms is that, phenomologically, catalysis can happen, and be observed, without any reference to reaction mechanisms--you throw some stuff in, and the reaction goes faster. Understanding what a catalyst *is* doesn't *require* much of an understanding of molecularity--look at biological catalysis for examples of just how widely this is true, where the reaction mechanisms are beyond the current ken of people who've been working on the problems for ages. Even so, they can observe and quantititate the rates with/without catalyst, with just bulk stoichiometry.

Granted, if you want to understand what the catalyst is doing beyond speeding the reaction, you need to get into molecular detail, and using reaction mechanisms to model happens is key to that.

Anyway, as with open source code, he who writes the stuff determines where it goes (at least, initially).

Just my 2 cents. You're putting some great stuff in here, so don't let my quibbling get in the way of that.

-- dja

Catalyst inhibitor

The article is generally well written and accurate, but there is just one more thing I would add. I was thought to believe that a catalyst "alters the rate of reaction." That is, a catalyst can either accelerate a chemical reaction or slow it down. A catalyst that slows down a chemical reaction is called an inhibitor. This has an important role in medicine. Since I'm not an expert on the subject, it would be great if someone could elaborate on this new and more accurate definition, as well as provide examples of its uses. A link to the "Inhibitor" page in Wikipedia would also be helpful.

NamelessOne

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I've gotten into arguments twice over the years that lead me to believe the definition of "catalyst" needs to be changed. I refer to the situation in which a sequence of reactions occurs in the reactor, wherein a catalyst of one reaction is a reactant in a later reaction and therefore cannot be recovered intact & quantitatively.

An example is saponification, which is commonly described as the base-catalyzed hydrolysis of an ester. The product of that reaction will include one or more acids, and the acid so produced will then neutralize the base catalyst stoichiometrically. So does one avoid referring to the base as a catalyst? Or does the definition of either "catalyst" or "reaction" need to change to keep the terms useful?

People invented the word "ribozyme" to keep the word "enzyme" as referring to a protein -- for a while the term "RNA enzyme" was used by those who wanted to expand the definition of "enzyme", and "catalytic RNA" by those who wanted to keep the distinction -- so clearly there's precedent for trying to keep the terms useful. (Heh -- of course the etymology, "in yeast", betrays obsolescence!)

robgood@bestweb.net

Catalyst Fouling

In actual chemical reactions on an industrial scale, it common for the catalyst to foul (become less effective) over time requiring it to be replaced with new ever so often. Some reaction mechanisms, or elementry reaction steps, require for one or more components to adsorb to the surface of a solid metal catalyst, react, and then desorb from the surface allowing other molecules to adsorb to the surface. (Look into Langmuir-Hinshelwood kinetics for more details.) Over time this process can cause the surface of the catalyst that works to decrease, lowering the effiency.

I believe that means that catalyst can be transformed.

Also, using the Ziegler-Natta catalyst in the production of high density polyethylene the catalyst initiates the polymerazation step and is in inturn trapped into the polymer matrix from which it can't slip free. Although the catalyst is unchaged, it can not be extracted and used again.

BeastRHIT

Speeds up reaction?

I think it would be more precise to say: A catalyst increases the rate of a reaction thus leading to a faster achievement of equilibrium compared to its uncatalyzed way, in which the catalyst itself stays unaltered and is not used up.

Nickel and Margarine

Do they really use nickel in the manufacture of margarine? I thought that nickel was quite toxic to people .. --Dirk Beetstra 20:02, 22 May 2006 (UTC)

Merger

It would be far better if this article is made into a redirect to Canalysis, and all the information put there. This is because a catalyst is part of the more general concept of catalysis. Catalysis is process that comprises the catalyst, the reactants, the products, the reaction conditions, and the reaction mechanism.   Andreas   ^(T) 16:13, 1 November 2006 (UTC)

Move discussion in progress

There is a move discussion in progress on Talk:Catalysis which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 15:46, 24 June 2021 (UTC)