Prevention of zeolite deactivation by coking

The deactivation of acid zeolite catalysts is essentially due to the formation and trapping of heavy secondary products (coke) within the pores (channels and cages). As in these nanosized pores the growth of these products is sterically limited, the coke composition, i.e., the quantitative distribution in nature and size of the components, can be determined and the scheme and mechanisms of coke formation established. Moreover, coupling activity, acidity and adsorption data with coke composition leads to information on the location and deactivating effect of coke molecules. Based on the influence on coking and deactivation rates of the features of reactions and zeolite catalysts, general rules are proposed for limiting the rate of formation of coke molecules and minimising their deactivating effect.