Study On Selective Catalytic Reduction Of NO From Exhaust Fumes By Low Hydrocarbon In The Presence Of Excess Oxygen

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. SCR of NOx by ammonia is maily used in the stationary NOx flue gases and ususal catalysts of SCR process are V₂O₅/TiO₂ catalyst. However, many probles exist in the industial application. Fortunately, a new method using hydrocarbon as reducing agent has attracted particular interest. But the catalysts used in the CxHy-SCR NOx reaction are sensitive to the reaction conditions. Recently, extensive efforts have been made to im prove the activity and selectivity of these catalysts. For the same consideration, we investigated some prospective catalysts and study on promoting the catalytic reduction activity of NO with propane and methane.For the first time, we chose cheaper metals loaded on ultra stable Y zeolite (USY) for the selective catalytic reduction of NO with propane. It was found that 15%Ni/H-USY was the most comparatively active among catalysts loading trasition metals, prepared by incipient-wetness impregnation. Then a series of experiments and characterization were made on the catalyst. Experimental results indicated that Ni/H-USY loaded 15% Ni can suppress effectively the formation of N₂O and CO. Synergistic effect of Ni ion and Brnsted acid might be responsible for catalytic activity and a mechanic path could be tested: NO oxided to NO₂ and then reduced to N₂. The new type catalyst samples were characterized by the measurements of BET, XRD, H₂-TPR, SEM and IR for pyridine adsorption and NO adsorption. The chemical analysis indicates that NiO distribute on the external surface of the zeolite particles. Synergistic effect between Ni²⁺ and B-acid is responsible for the SCR of NO on Ni/H-USY. Nitrate compounds of Ni²⁺ formed on Ni/USY after NO adsorption are favor of the reduction of NO with propane.In the experiment, we found that the catalyst of USY is much active for the reduction of NO₂ to N₂. So we can make use of metal/Al₂O₃ which has been proved to be active sites for NO to NO₂ to mix with H-USY zeolite to enhance the reduction of NO. Experimental results on all the catalysts studied show that the NO conversion to N₂ over the physical mixture catalysts was higher than that expected if these components acted independently under the condition of keeping gas hourly space velocity constant. Morover, the mixture of Mt/ γ- Al₂O₃ and H-USY zeolite can simultaneously increase the N₂ yield, decrease the N₂O yield, consequently increasethe N2 selectivity for CsHg-SCR and, in particular, improve remarkably the Sscr of the C3H8 + NO + O2 system. Such synergistic effect of metal oxide and proton acid was discussed and possible reason was proposed that high temperature makes metal cation easy to migrate into zeolitic channels and consequently became the active site for C3Hg-SCR of NO. It is possible that Br0nsted acid on H-USY zeolite is the most important driving power.For the first time, we adopt a new type catalyst of Magnesium-Aluminum oxide loading metal for the SCR of NO. Experimental results indicated that Ag/MgAlO was the most comparatively active and applied compared with catatysts in many researches. Especially, it was stable in the presence of 15% water and 100 ppm SO2 showing prospective for the future industrial application. Last, kinetics was also studied and discussed.