An obviously absurd consequence of the second law of thermodynamics is that a catalyst speeds up the forward and reverse reactions equally (by exactly the same factor). In other words, the catalyst cannot shift the position of equilibrium:

"In the presence of a catalyst, BOTH THE FORWARD AND REVERSE REACTION RATES WILL SPEED UP EQUALLY, thereby allowing the system to reach equilibrium faster. However, it is very important to keep in mind that the addition of a catalyst has no effect whatsoever on the final equilibrium position of the reaction. It simply gets it there faster. [...] If the addition of catalysts could possibly alter the equilibrium state of the reaction, this would violate the second rule of thermodynamics..." https://courses.lumenlearning.com/introchem/chapter/the-effect-of-a-catalyst/

Scientists should have noticed the obvious absurdity of this particular consequence of the second law of thermodynamics long ago, and applied reductio ad absurdum: Since the consequence is absurd, the underlying premise, the second law of thermodynamics, is false.

Consider the dissociation-association reaction

A ⇌ B + C

which is in equilibrium. We add a catalyst and it starts splitting A - the rate constant of the forward (dissociation) reaction increases by a factor of, say, 745492. If the second law of thermodynamics is obeyed, the catalyst must increase the rate constant of the reverse (association) reaction by exactly the same factor, 745492. But this is insane! The reverse reaction is entirely different from the forward one - B and C must first get together, via diffusion, and only then can the catalyst join them to form A. Catalysts don't speed up diffusion!

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"The second law of thermodynamics describes why a catalyst does not change the chemical equilibrium of a reaction. Suppose there was such a catalyst that shifted an equilibrium. Introducing the catalyst to the system would result in a reaction to move to the new equilibrium, producing energy. Production of energy is a necessary result since reactions are spontaneous only if Gibbs free energy is produced, and if there is no energy barrier, there is no need for a catalyst. Then, removing the catalyst would also result in reaction, producing energy; i.e. the addition and its reverse process, removal, would both produce energy. Thus, a catalyst that could change the equilibrium would be a perpetual motion machine, a contradiction to the laws of thermodynamics." https://en.wikipedia.org/wiki/Catalysis

The above text is extremely silly and confusing, but it can be improved in this way:

The second law of thermodynamics describes why a catalyst does not change the chemical equilibrium of a reaction. Suppose there was such a catalyst that shifted an equilibrium. Introducing the catalyst to the system would result in a reaction to move to the new equilibrium, producing energy that can be harnessed to do mechanical work. Then, removing the catalyst would result in the reaction to return to the old equilibrium, the lost (converted into work) energy being restored endothermically. Thus, a catalyst that could change the equilibrium would be a perpetual motion machine of the second kind, a contradiction to the second law of thermodynamics.

Since catalysts CAN change the equilibrium of chemical reactions, the following pompous claim is correct:

Potentially, any catalyst is a perpetual motion machine of the second kind.

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Pentcho Valev