Catalysts are subject to a variety of factors during use and can lose their activity either sharply or slowly. The causes of catalyst deactivation are complex. They can be summarized into some categories as follows.

At present, the role of the catalyst is not fully understood. In most cases, it is believed that the catalyst itself participates in the chemical reaction along with the reactants, reducing the activation energy required for the reaction. Some catalytic reactions are due to the formation of easily decomposable "intermediates", when the decomposition of the catalyst restores the original chemical composition, the original reactants become products.