Study On Catalytic Reduction Of NO_x By NH₃over Cerium Based HBEA Zeolites Catalys At Low Temperature

In a variety of atmospheric pollutants, the nitrogen oxide （NO_x） is an increasing concernin recent30years. The nitrogen oxide can cause Photochemical smog, acid rain and so on,which leads to the destroying of environment and human beings’ respiration disease has beenproved. SCR technology is the most mature commercial flue gas denitration technology. Butlow activity at low temperature, Poor SO₂resistance of catalysts and uncertainty of reactionand SO₂-Poisoning mechanisms are the main obstacle of the industrial application.Therefore, this work was carried out the following aspects:To imProve the selectivity atlow temperature in the selective catalytic reduction（SCR） of NO_x, the performance of thecatalysts prepared by incorporating cerium to HBEA zeolite was investigated for the SCR ofNO by using NH₃as reducing agent. we investigated the effects of second additives onCe/HBEA catalysts in this dissertation.The influence of the cooperating agents was studied onthe activity of catalysts for NH₃-SCR in different reaction condition，which furthermore couldcombine with the catalyst structure.The Ce/HBEA catalyst was prepared by homogeneous co-precipitation method. Theeffects of preparation conditions including active component ratio, loading along withcalcination temperature and operating conditions, NH₃/NO_xmolar ratio, NO_xconcentrations,space velocity and O₂concentrations on activity of catalyst Ce/HBEA for selective catalyticreduction of nitric oxides by NH₃at low temperature were investigated. The influences ofH₂O, SO₂were also discussed in this work. The catalysts were characterized by specificsurface area （BET）, X-ray diffraction （XRD）, scanning electron microscope（SEM）,thermogravimetry （TG） and Fourier transform infrared spectroscopy （FT-IR）.The resultsshowed that catalyst with n（Ce） loading10%, calcination temperature450℃performed highNO_xconversion of over96.4%at the conditions of NO_xinput concentrations0.06%, O₂concentrations6%, space velocity12000h-1, reaction temperature220℃and NH₃/NO_xmolar ratio1.1. NO_xconversion could be kept over95%in temperature（220⁴00℃）andspace velocity（12000³6000h-1）test. The catalyst’s activity was little affected at thepresence of H₂O above temperature220℃.To some extent, SO₂inhibited the catalyticactivity at lower temperature, but the activity could be partly restored when the temperatureincreased. Consequently, CeO₂/HBEA catalyst had good resistance to sulfur and waterpoisoning performance. Study on deactivated mechanism of Ce/HBEA catalyst by the FTIRtest, It showed that （NH4）2SO4and NH4HSO4were major cause for catalyst deactivation.Adding addictives to Ce/HBEA aimed for enhancing its activity and poison-resistance- capability at low temperature. Results showed that addictive Fe could advance Ce/HBEA’slow temperature activity, and increased its inherent SO₂、H₂O resistance-capability.Compared with other catalysts, The Ce/HBEA and Fe-Ce/HBEA catalysts wasinvestigated to provide possible guidances for industrial application. Especially their lowreaction temperature on catalyst activity and good resistance to sulfur and water poisoningperformance.