Catalyst of a Reaction

Question

Consider the following reaction

2 AX + 2 I → 2 AI + 2 X

where the following mechanism has been proposed:

2 AX + B → A_2B + 2 X

A_2B + 2 I → 2 AI + B

My question is what is the catalyst in this reaction and why?

Answer 1

To find a catalyst, look for something that is present at the beginning and at the end of the reaction, in an unchanged form. That is the definition of a catalyst. In the current situation, we see that that B is a reactant in the first step, and it is a product in the last step. So it remains unchanged and this satisfies the definition of a catalyst. So, B would be the catalyst.