Novel catalyst development for NOx removal from diesel engine emission

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Pd/ZSM-5 catalyst shows characteristic features on NO-CH_4-selective reduction reaction, for example, high stability under excess O_2 and steam condition, high activity, and so on. So this catalyst seems to be a good candidate for lean burn combustion of natural gas at high temperature. So far, this catalyst has one defect, which is hydrothermal stability. One of the solutions is exploring new additive like Co. We conducted several attempt for the improvement of this catalyst, and one of the goal is Fe addition for solving these problems.First, we prepared Pd/ZSM-5, PdFe/ZSM-5, Fe/ZSM-5 catalysts. Experiments were conducted under atmospheric pressure and using fixed bed reactor.As for the activity and stability of Pd/ZSM-5 and PdFe/ZSM-5 catalysts, PdFe/ZSM-5 showed high NO conversion as high as 55.2%, and it was rather higher than that of Pd/ZSM-5, 42.2%. And there were no difference on the stability of catalyst between these two catalysts. We supposed that there are two different active sites on this Pd/Fe/ZSM-5 catalyst, because Fe catalyst did not show any activities on NO-CH_4-selective catalytic reduction.So, we postulated that Fe/ZSM-5 catalyst is only effective under the existence of activated carbon species like activated hydrocarbon formed on Pd site