What is the role of catalyst in various reactions?

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Discussion Overview

The discussion revolves around the role of catalysts in various chemical reactions, specifically focusing on processes such as the Haber process, hydrogenation of alkenes, and methanol synthesis. Participants explore the mechanisms of heterogeneous catalysis and the selection criteria for different metals as catalysts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the role of catalysts in specific reactions, such as the Haber process and methanol synthesis, and seeks clarification on their functions.
  • Another participant explains that the processes mentioned are examples of heterogeneous catalysis, where reactants adsorb to the catalyst surface, weakening bonds and increasing effective concentration.
  • Questions arise regarding the criteria for selecting specific metals as catalysts, with one participant suggesting that iron is used in the Haber process due to its efficient adsorption of nitrogen.
  • Another participant notes that the selection of catalysts can be experimental and somewhat arbitrary, describing it as "voodoo."
  • There is a discussion about why certain metals, like iron, are better at adsorbing specific gases, with a suggestion that iron's variable oxidation states may contribute to its suitability.
  • A later reply mentions practical considerations in catalyst selection, highlighting that iron was historically chosen for its cost-effectiveness compared to other metals like ruthenium or osmium, despite their superior catalytic properties.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the role of catalysts and the criteria for their selection, indicating that multiple competing views remain on the topic. The discussion does not reach a consensus on the specific reasons for the effectiveness of certain metals as catalysts.

Contextual Notes

Participants acknowledge the complexity of catalyst design and the ongoing challenges in understanding the detailed molecular processes involved, suggesting that there are limitations in current knowledge and methodologies.

jd12345
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There are many reactions in which i don't understand what the role of catalyst is.

Reactions like hydrogenation of alkenes , use of Ni i understand - it kinda breaks the hydrogen-hydrogen bond and provide it for the alkene.
In contact process i.e. SO2 + 1/2O2 ----> SO3 catalyst is V2O5. I understand this as V2O5 reacts with SO2 to provide oxygen and then oxidses

But i don't understand catalyst in reactions like :- habers process i.e. N2 + 3H2 ----> 2NH3
catalyst is Fe but what is its role?
similarly CO + 2H2 ---> CH3OH catalyst is cobalt but what is its use??
CH3OH ----> HCHO + H2 catalyst is heated copper but how does it remove hydrogen

Plz tell me what are the role of catalyst in these 3 reactions -
There are many other reactions where catalyst are used and i don't understand but its not possible to ask them all so if you can tell me in general too it'll be very helpful
 
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The processes you mention are all cases of heterogeneous catalysis. You have a catalyst (typically a solid in many applications) and the reactants adsorb to the surface. The bond weakens, such as in N2, with a triple bond between the nitrogen atoms. You also can gain an increase in effective concentration (instead of the reactants just floating around in the gas or liquid phase, they're all now adsorbed to the catalyst surface).

Be sure to read the link, and I would Google "heterogeneous catalysis." There's plenty of information out there, as it's both an example of really interesting chemistry but also very practical chemistry.
 
how do we determine which metal to use in which reaction?
example: in habers process iron is used. This might be because it adsorbs nitrogen very efficiently. But what makes it such a good adsorbent of nitrogen?
 
jd12345 said:
how do we determine which metal to use in which reaction?

Experimentally.

From what I know selecting catalysts is still kind of a voodoo.
 
okay, but the question is :- why do certain metals adsorb specific gases better than others? Iron is used in habers process, why?
There must be some reason!
 
jd12345 said:
okay, but the question is :- why do certain metals adsorb specific gases better than others? Iron is used in habers process, why?
There must be some reason!

Possibly due to the Iron having few variable oxidation states that makes it more suitable than say, Manganese.
 
For the Haber-Bosch process, at least, there's an element of pure practicality. Back in the day, using iron was cheaper/less troublesome than getting an adequate amount of ruthenium or osmium (which are better catalysts, although I think there was also an issue with catalytic lifetime/catalyst poisoning, but don't quote me on that). The process is also sensitive to the surface topography.

Like Borek said - catalyst design still has vast amounts of voodoo in it. While there are methods to investigate the detailed molecular processes at work, there is still a long way to go before we can design catalysts off the top of our head and have them work just as we expect.
 
ok thank you
 

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