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I searched that an reversible reaction can be made irreversible by removing its product.

I am wondering if catalysts can help produce the same effect. And I'd also like to know, if actually an irreversible reaction can be made reversible.

Please give me some examples if possible, thanks!

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Keeping a reaction away of its equilibrium by removing products does not make it irreversible, just "effectively irreversible". Catalysts do not change it, as they affects reaction rates, but not the equilibrium position. Removal of reaction products can be faster, as they would be formed faster.

Note that truly irreversible reactions are rare. They are those that do not have an equilibrium. Typical (nuclear, not chemical) irreversible reactions are radioactive decays.

It is usually like the equilibrium of a reversible reaction is shifted so far to right it is effectively irreversible.

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  • $\begingroup$ An equilibrium reaction is by definition reversible. At equilibrium forward and reverse reactions have equal rates. $\endgroup$
    – jimchmst
    Commented Mar 11 at 8:57
  • $\begingroup$ @jimchmst Sure, this is widely known. $\endgroup$
    – Poutnik
    Commented Mar 11 at 9:04
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    $\begingroup$ Then revise you last sentence to show that. $\endgroup$
    – jimchmst
    Commented Mar 11 at 19:25
  • $\begingroup$ Or, revise your interpretation of it. $\endgroup$
    – Poutnik
    Commented Mar 11 at 19:32
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    $\begingroup$ Radioactive decay is technically reversible too, and has an equilibrium. It's just that these equilibria tend to be very hard to reach outside the core of a star or a supernova explosion. The reason why nuclear decay is practically irreversible is basically the same as for e.g. the decomposition of nitroglycerine or other similar explosives: in either case, both entropy and energy very much favor the products. $\endgroup$
    – Ilmari Karonen
    Commented Mar 11 at 21:09
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The equilibrium of a specific chemical reaction cannot be in general 'changed from the outside', unless the temperature is changed accordingly. However, an equilibrium reaction may seem to be irreversible if we remove the products selectively, although I don't like the wording that you use. We are not altering the equilbrium, rather allowing the forward rate of reaction to keep marching on.

One simple application of this is a membrane catalytic reactor for dehydrogenation of alkanes. These reactions are limited by equilibrium. In the following image we can read the equilibrium conversion $X_\mathrm{eq}$ of several alkanes as a function of temperature $T$:

enter image description here

Even though the temperature is very high, more than $\pu{50 \%}$ of the reactant will just sit in the reactor if it is long enough. But, in this particular reaction we may eliminate the hydrogen gas generated through a permeable membrane, which we illustrate for ethane: $$ \ce{C2H6(g) <=> C2H4(g) + H2(g) v} \tag{1} $$ A scheme of the procedure is the following:

enter image description here

The idea is very simple, we remove hydrogen so the reaction can continue. If we keep doing this, the reaction may seem to be irreversible as we will find a negligible amount of reactant at the end of the reactor. We will walk at the outlet of the reactor and find $\approx \pu{0 mol dm^{-3}}$ of ethane, but the reaction in inherently reversible.

As a remainder, this is a very delicate process, because it would be a huge problem if ethene or any other alkene entered the gas stream along with hydrogen. Since the wanted product is the alkene, we would further need a separation process of it an hydrogen, which would be a waste of money. The key element is the solid membrane, whose structure must not intefere with the reaction and only serve the purpose for the small hydrogen molecules to pass through them via a mass transport process.

References

The $X_\mathrm{eq}$ vs $T$ graph was taken from:

The image of the membrane catalytic reactor is found in this work:

  • Shelepova, E. & Vedyagin, Aleksey. (2021). Theoretical Prediction of the Efficiency of Hydrogen Production via Alkane Dehydrogenation in Catalytic Membrane Reactor. Hydrogen. 2. 362-376. 10.3390/hydrogen2030019.
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