Selective Catalytic Oxidation (SCO) Of Ammonia To Nitrogen Over Mesoporous And Microporous Zolites

It is known that many chemical processes (Nitrate-containing, N fertilizers, petroleum refining, etc) use reactants containing ammonia or produce ammonia as a by-product. Hence, the removal of NH3from waste gas streams is becoming increasingly important in terms of environmental protection. There are many ways to remove NH3, including biological, physical and chemical treatment processes, among which selective catalytic oxidation (SCO) of NH3to N2is an ideal technology for removing NH3from waste gases, and it has been of increasing interest in recent years. A number of catalysts have previously been applied to oxidize gaseous NH3:noble metal catalysts were active for the reaction of SCO of NH3at low temperature, but the selectivity of N2was not satisfied for the reason that the main by-product at low temperature was N2O; transition metal oxides supported catalysts showed high catalytic activity and N2selectivity but the temperature of the reation was very high; and the carrier they used was nun-pore arrangement and small surface area. For the zeolite, due to its superhigh surface area, ordered pore arrangement, adjustable pore sizes and high hydrothermal and thermal stability, it has become the excellent catalyst support.A series of mesoporous zeolite catalysts (Cu, Co, Fe, Mn, Ni)/SBA-15, Cu/(SBA-16, KIT-6), microporous zeolite catalysts (Cu, Co, Fe, Mn, Ni)/ZSM-5, Cu/(Beta, Y, FER, MOR, MCM-49) and different carriers catalysts Cu/(SiO2, Al2O3) and noble metal catalysts (Ag, Pt, Pd)/ZSM-5were prepared and were then fully characterized using traditional techniques (XRD, BET, H2-TPR, XPS) as well as advanced oxygen isotopic exchange and equilibration techniques.It was shown that among mesoporous zeolite catalysts Cu/SBA-15obtained an outstanding NH3-SCO performance in a wide temperature window (from100℃to500℃); for microporous zeolite catalysts Cu/ZSM-5displayed the best; and Cu/ZSM-5also shows better when compared with noble metal and different carriers catalysts. Finally, the oxygen mobility was evaluated in Cu/SBA-15, Co/SBA-15and Cu/zeolites. While the Co/SBA-15shows a high surface oxygen mobility but only have a limited bulk oxygen mobility, but its oxide ability seems too strong for NH3combustion (transformed redundant NOX). For the three Cu/zeolites, they all remained a good oxide surface characterization due to the limited participation of the bulk oxygen atoms, and Cu/SBA-15shows the strongest oxygen mobility. The rate of P34rise follows a decreasing order of Cu/SBA-15> Cu/SBA-16>Cu/KIT-6, and18O fraction in the gas phase αgt is as follows:Cu/SBA-15> Cu/KIT-6≈Cu/SBA-16(the same with the activity test). Indicated that the catalytic performence was related with the participation of the bulk oxygen atoms:the more the participation of the bulk oxygen atoms was in, the better the catalytic performance was obtained. In summary, above these study it can be known that Cu/ZSM-5is a promising candidate used as a catalyst for NH3selective combustion towards unharmful N2.