Selective Reduction Of Nitrogen Oxides By Hydrocarbons Over Cu/Al₂O₃ Catalysts Under Oxygen-Enriched Conditions

Today,with increasingly serious environmental problems,people are increasingly demanding emissions from industrial and automotive emissions.Acid rain and other pollutants formed by a large amount of nitrogen oxides in exhaust emissions not only cause irreversible damage to biological and urban environments,but also greatly endanger people's health.Therefore,in order to effectively eliminate the content of nitrogen oxides in the atmosphere,the exploration and research and development of corresponding elimination means is urgent.So far,people have made a persevering exploration to eliminate harmful nitrogen oxides in the air.Among them,selective catalytic reduction of nitrogen oxides?SCR?is one of the most efficient means of removing nitrogen oxides.Among the reactions of hydrocarbon selective reduction nitrogen oxides?HC-SCR?to remove automobile exhaust gas under oxygen-rich conditions,nitrogen oxides are a promising method for elimination.In this experiment,XRD,BET,SEM,TEM and other methods were used to characterize the catalyst.The reaction process was evaluated by MS-TPD.The purpose was to investigate the different loadings of different copper sources?Copper sulfate,Copper nitrate?and copper?The effect of1 wt%,2 wt%,3 wt%,5 wt%?on the selective reduction of nitrogen oxides.?-Al₂O₃ is used as a carrier,and because of its low price and easy availability,it is more common in the field of catalysis.Cu/?-Al₂O₃catalysts with different loadings were prepared by equal volume impregnation method?loading capacity:1 wt%,2 wt%,3 wt%,5 wt%,respectively?at different temperatures to explore the N_xO_x-SCR reaction with C₂H₂ as a reducing agent at 150 ^oC,200 ^oC,250 ^oC,300 ^oC,350 ^o C,400 ^oC,450 ^oC,500 ^oC,550 ^oC.At the same time,this paper also investigates the effects of ghost monitoring and H₂ condition on the low temperature reactivity of the catalyst and the effect of different air-to-air ratios on the conversion of nitrogen oxides.According to the experimental results,it can be found that the catalytic activity of Cu/?-Al₂O₃ catalyst prepared by Cu?NO₃?₂ is better.Among the different copper loading catalysts,3 wt%Cu/?-Al₂O₃ catalyst has better effect and its nitrogen oxide conversion The rate can reach more than 50%.The 5 wt%Cu/?-Al₂O₃ catalyst has the worst effect,and the nitrogen oxide conversion rate is only about 40%.Under hydrogenation conditions,1 wt%Cu/?-Al₂O₃ catalyst has better effect,its nitrogen oxide conversion rate can reach 58%,5 wt%Cu/?-Al₂O₃ catalyst has the worst effect,and the nitrogen oxide conversion rate is only about 40%.Compared with the Ag/?-Al₂O₃ catalyst,the properties of the two catalysts are similar,but the Cu/?-Al₂O₃ catalyst has a good low temperature activity,and the conversion rate of nitrogen oxides at 300 ^oC could reach about 50%.And adding a small amount of precious metal?Au?to the catalyst,and?-Al₂O₃ modified by Au-Cu further enhances the low-temperature activity of the catalyst,and the conversion rate of nitrogen oxides can reach 30-40%at 250°C.The Cu/?-Al₂O₃ catalyst removes NO_x and obtains higher conversion rate at lower temperature.For example,in 1500 ppm C₂H₂/500 ppm NO/10%O₂/N₂,the reaction temperature is 300 ^oC-350 ^oC,and the space velocity is under the condition of 15000 h^-1,the NO_x conversion rate can reach the highest conversion rate under different loadings of Cu/?-Al₂O₃catalyst.Different space velocity,different carbon-nitrogen ratio,conversion to NO_x and C₂H₂ have a certain impact.The catalyst promotes the decomposition of the nitrogen-containing adsorbed species formed on the catalyst during the adsorption process.The experimental results show that in the process of NO desorption,there will be NO₂ formation,and there will be decomposition of NO and NO₂.During the desorption of Cu/?-Al₂O₃ catalyst,as the temperature increases,nitrogen oxides will decompose to N₂,and the nitrogenous species formed during desorption will also generate N₂ and O₂.