deadrush
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Activating a catalyst
I know this is very basic and obviously written and explained in a plethora of places but...
I have searched far and low for over a year for exactly what is and how to activate a catalyst. I mean if i pack a copper tube with copper mesh and
lead 400C methanol vapor through it, i should end up with at least some formaldehyde. How is activated copper different? Is it only increased surface
area? What about nickel catalyzed hydrogenation of napthalene? Could i just use nickel metal? And how does one activate say, "oxone"? I understand its
the HSO5 ion thats important but it would seem to me that simply dissolving it in water would activate it then.
Ive had this question a long long time, sorry if it came off a little... frustrated?
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Texium
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This is an extremely vague question. One part is easy to answer, and the other part is impossible.
1. What is a catalyst? Anything that increases the rate of a reaction by providing an alternative pathway with lower activation energy, and isn’t
consumed in the reaction.
2. How do you “activate” a catalyst? Not possible to answer. It is case by case depending on the catalyst in question, and it might be entirely
irrelevant. Some things don’t need to be “activated” in order to have catalytic activity, or may or may not need to be depending on what
you’re using them for. For heterogeneous metal catalysts, yes, surface area is generally an important factor. But it’s a very complex subject with
many contributing factors.
This seems to be a case of you couldn’t find an answer because you’re asking the wrong questions. I recommend you do some textbook reading on the
fundamentals of catalysis, and then come back when you have a general understanding and can ask specific, focused questions.
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Texium
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Thread Moved
17-10-2023 at 18:51 |
j_sum1
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Let me break this down into a few cases. Like Tex, I doubt I can answer all your questions, but at least this will give you the scope needed.
Activation is a pretty loose term.
Heterogenous catalysis is going to take place at a surface -- typically the surface of a solid immersed in a gas or liquid. "Activation" would mean
taking steps to increase the surface area: generally by decreasing particle size or increasing porosity. But it could mean bonding it onto a
substrate or applying some kind of surface treatment. It could also mean taking steps to remove product/byproduct from the surface so that reagents
are not physically obstructed from reaching the reaction site.
Homogeneous catalysis occurs in a single phase. Let's say two completely miscible liquids. You may need to take some steps to ensure that the
liquids are miscible and that the mixture is properly stirred. You may need to prepare the catalyst itself. For example creating a transition metal
complex that interacts with your reagents in a way that is favourable. It is all very well to say that ruthenium catalyses polymerisation of
ethylene. But the reality is that you would need to prepare the appropriate ruthenium compound for your particular process.
Biology is replete with highly specialised catalysts aka enzymes. These may be activated by having them at the correct temperature or pH or attaching
them to (or detaching them from) other agents that may be in the mixture.
Activation is a rather nebulous term that could cover a range of situations. It really depends on your application. Most of the situations I have
dealt with are heterogenous catalysts. Activation in these situations would basically mean increasing the surface area as much as possible.
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BromicAcid
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My guess would be to run hydrogen over it hot to reduce any oxide coating and leave the free copper sites. Then again the active catalyst could
potentially be copper oxide, it might just need air run over it hot. Or it could be some kind of carbonate which might want hot air/CO2. Anything I
say is a guess but in any case you're trying to make more active sites, just depends on what active site the reaction is looking for.
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