Selective Catalytic Reduction Of NO With Methane Over The ZSM-5 Based Catalysts

The selective catalytic reduction (SCR) of NOx to N2 in the presence of excess oxygen is an important commercial process to remove pollutants from exhaust fumes. The using of methane as reducing agent has attracted particular interest, since methane is almost present in all combustion exhausts. But the catalysts used in the CH4-SCR NOx reaction are sensitive to the reaction conditions. Recently, extensive efforts have been made to improve the activity and selectivity of these catalysts. For the same consideration, we investigated the effects of second additives on the Co/HZSM-5 and In/HZSM-5 catalysts respectively in this dissertation.For the first time we chose cheaper metals as cooperating agents for Co/HZSM-5 and investigated the effect of these metal oxide additives for the selective reduction of NOx with methane. It was found that the addition of Zn could effectually heighten the selectivity of methane to NOx. TPD results showed that Zn contributed the form of NO2 and strengthen its adsorption on the Co/HZSM-5 catalyst. The results of H2-TPR and XPS further proved that addition of Zn into Co/HZSM-5 could inhibit the formation of bulk Co3O4. The reducing of bulk Co3O4 will restrain the combustion of methane and improve the selectivity of methane to NOx, which could combine with the experimental results well.In this dissertation, we found that colloidal alumina not only acted as a binder to enhance the mechanical strength of the catalyst, but also improved the activity of In/HZSM-5 catalyst for the selective reduction of NO with CH4 in the excess of oxygen. The results of TPD showed that the addition of AL2O3 enhanced the adsorption of NO2 on the catalyst, broadened the range of reaction temperatures and facilitated the activation of methane. Some characterization techniques such as H2-TPD, TEM and BET were also used. The results exhibited that the addition of colloidal alumina increased the BET surface area and the pore volume, led to the In species moved from the outside surface of the In/HZSM-5 catalyst to inside surface, which resulted in the more InO+ active sites formed. InO+ active sites could adsorb NO2 molecule, which would accelerate the whole SCR reaction, In order to further improve the function of In species in the pole of ZSM-5, we added a little In2O3 into In/HZSM-5 directly and found the activity of catalyst was also enhanced.