Novel catalyst development for NOx removal from diesel engine emission

Pd/ZSM-5催化剂在NO-CH4选择性还原反应中表现出对过量O2和水蒸气条件下的高稳定性、高活性等特点。因此，该催化剂是天然气高温稀燃燃烧的一种很好的选择。到目前为止，这种催化剂有一个缺点，那就是水热稳定性。其中一个解决方案是探索新的添加剂如Co。我们对该催化剂进行了多次尝试，其中一个目标是添加Fe来解决这些问题。首先，我们制备了Pd/ZSM-5、PdFe/ZSM-5、Fe/ZSM-5催化剂。对Pd/ZSM-5和PdFe/ZSM-5催化剂的活性和稳定性进行了研究，PdFe/ZSM-5催化剂的NO转化率高达55.2%，远高于Pd/ZSM-5催化剂的42.2%。两种催化剂在催化剂稳定性上没有差异。我们推测Pd/Fe/ZSM-5催化剂上存在两个不同的活性中心，这是因为Fe催化剂对NO-CH4-选择性催化还原没有表现出任何活性，所以我们推测Fe/ZSM-5催化剂只有在Pd中心上生成的活性碳类等活性碳物种存在的情况下才有效

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