Preparation Of Copper-molybdenum,Cobalt-iron And Ferro-molybdenum Composite Oxides And Their Studies In Selective Catalytic Reduction Of NO_x

Nitrogen oxide?NO_x?is one of the main pollutants that cause the air pollution,which has caused serious harm to the environment and human health.Ammonia selective catalytic reduction of nitrogen oxides?NH₃-SCR?technology can effectively remove NO_x without secondary pollution.This paper faced on the NO_x eliminate problem in mobile source,adjusting the acidity,NO_x adsorption capacity and oxide performance of catalyst,copper molybdenum,cobalt iron and iron molybdenum compound oxide were synthesized,respectively.The physical structure and electronic properties of catalyst were analyzed,and the structure-activity relationship was revealed.Meanwhile,the main active species and reaction pathway were explored by mass spectrometry and in-situ infrared spectroscopy.The main research achievements are as follows:?1?Copper molybdenum solid solution with“Cu-O-Mo”structure was prepared.Compared with CuO,the formation of“Cu-O-Mo”structure reduced the particle size by 5-10times and increased the specific surface area by 3-8 times,which promoted the transfer of mass and heat.Moreover,the structure enhanced the electronic interaction between Cu and Mo,increasing the amount of Br?nsted acid,and inhibited the generation of?NH₄?₂SO₃/?NH₄?₂SO₄,thus improving the low-temperature sulfur resistance.The increase of adsorption capacity of ammonia and nitrate reduced the reaction activation energy,and the reaction activity and N₂ selectivity were significantly improved compared with CuO.In the temperature range of 175-275^oC,the NO_x conversion over copper molybdenum solid solution reached 80%,and N₂ selectivity were improved by 10%.?2?The Co-Fe composite oxide was synthesized by hydrothermal method,and the effects of composite structure with“interface interaction”on catalytic activity and physical-chemical properties were explored for studying the structure-activity relationship.The co-existence of Fe₂O₃ and CoFe₂O₄ spinel in cobalt iron composite oxide strengthened the electronic interaction and REDOX properties.Not only improved the oxidation performance,increased the ad-nitrate species amount;but also increased the Lewis acid and ad-NH₃ amount.NO_x conversion over catalyst was above 80%in the temperature window of 200-350^oC and the active window could still be maintained at 225-300^oC under high airspeed condition of120000 h^-1,which showed a good resistance to high airspeed.Compared with CoFe₂O₄ spinel,the temperature window was widened by 50^oC and the NO_x conversion rate increased by 10%.The in situ DRIFTS results showed that the main ad-NH₃ was coordination NH₃ while NO_x species were nitrite,nitrate species and gas-NO₂,followed L-H and E-R pathway.?3?Ferro-mo composite oxide with wide temperature window was prepared by urea precipitation method.The?-Fe₂O₃ and Fe₂?MoO₄?₃ species crossed each other to form an"interface".Fe₂?MoO₄?₃ species with Mo=O structure provided abundant Br?nsted acid sites;the strengthened interfacial electronic interaction promoted the increase of Lewis acid on the catalyst surface.Over 80%NO_x conversion and N₂ selectivity could be achieved within the temperature range of 200-425^oC.Under the airspeed range of 180,000 h^-1,the activity temperature windows could be maintained within 225-425^oC.Even in the environment of2000 ppm SO₂,the temperature operating window of catalyst could still be sustained at225-425^oC.Coordination NH₃ and NH₄⁺species were the main NH₃ ads-species in the NH₃-SCR reaction,which not only could react with nitrate and nitrite ad-species through the Langmuir-Hinshelwood pathway,but also could also react with gaseous NO₂ followed the Eley-Rideal reaction pathway.