catalyst does not consume during the curse of the reaction but speeds up the chemical reaction, Catalyst will not appear in the overall reaction but will appear in every step of the mechanism.
Effect of catalyst
It lowers the rate of reaction.
They provide a means for reactant molecules to break bonds and form a temporary bond with the catalyst.
For example, pt metal serves as a catalyst for many reactions involving oxygen gas or hydrogen gas. This happens because the pt surface allows the hydrogen or oxygen to break their bond and then form atomic species which are ‘bonded’ to pt.