The catalyst is what appears exactly the same at the end and appears early in the equation set. In this case Cl(g).The intermediate appears "intermediately" not at the beginning or at the end, but is made and consumed in the middle. Like ClO(g). A substance that is regenerated in the next is a catalyst and is consumed in the first step. In contrast, when a substance is formed in the first step and is consumed in the next step, then it is known as an intermediate.