Combinatorial chemistry is an efficient technique for the synthesis and screening of a large number of compounds. Recently, we introduced the combinatorial approach to computational chemistry for catalyst design and proposed a new method called 'combinatorial computational chemistry'. In the present study, we have:applied this combinatorial computational chemistry approach to the design of deNO(x) catalysts. Various ion-exchanged ZSM-5 are candidates as catalysts for the removal of nitrogen oxides (NOx) from exhaust gases in the presence of excess oxygen. Here, we describe the screening of the exchange cations in ion-exchanged ZSM-5 which are strong against poisons. We investigated the adsorption energies of NO and water on various ion-exchanged ZSM-5 catalysts. Cu+, Ag+, Au+, Fe2+, Co2+, Ni2+, Pd2+, Pt2+, Cr3+, Fe3+, Ir3+ and Tl3+ were found to have high resistance to water molecules during the deNO(x) reaction.