Preparation And Performance Study Of β Molecular Sieve-based Denitration Catalyst

With the rapid development of human civilization and industrial production,a large number of production and domestic waste gases are generated and discharged into the atmospheric environment,resulting in the continuous deterioration of air quality.The nitrogen oxides（NO_x）emitted during the use of fossil fuels are an important reason for the deterioration of air quality.Therefore,it is very important to develop new efficient denitration catalysts to control NO_xpollution.In this paper,the denitrification performance of Fe/beta catalyst was effectively improved by physical combination of Mn based catalyst and chemically doped Ce or Pr cocatalyst.Mn based catalyst has good activity at low temperature,and Fe/beta catalyst has excellent thermal stability.When Fe/beta catalyst is placed upstream of Mn based catalyst,the activity temperature window of the composite catalyst is greatly widened compared with that of component catalyst,and the preferential action of upstream Fe/beta catalyst at high temperature can effectively inhibit the side reaction of downstream Mn_x/Ti O₂catalyst.The combination where Fe/Beta is placed upstream of the Mn-based catalyst is called the“effective combination”.Four kinds of supported Fe/beta catalysts were prepared by impregnation method.Among them,4wt%Fe/beta（4Fe/beta）has the best catalytic performance,when it is combined with Mn_x/Ti O₂catalysts with different Mn loadings at the volume ratio of 1:1 according to the“effective combination”mode,the activity of 4Fe/beta-Mn_0.4/Ti O₂（4FB/0.4MT）is the best,the conversion of NO can keep above 90%in the range of 200-500℃,and the by-product N₂O concentration is only 37ppm at the highest.The selectivity of N₂O for4FB/0.4MT（1:1）at medium and low temperature（<300℃）increases continuously,which is mainly caused by the increase of the key intermediate-NH in the reaction process.The 4Fe/Beta-Fe_0.1Mn_0.4/Ti O₂（1:1）composite sample is prepared from Fe/Beta and Fe-doped Mn_x/Ti O₂,and its low temperature activity is higher than4FB/0.4MT（1:1）.Ce or Pr doping can effectively improve the high temperature performance of Fe/beta catalyst.When the reaction temperature is 600℃,the performance of Ce-Fe/beta catalyst is improved by 3.3%,and that of Pr-Fe/beta catalyst is improved by 4.2%;for the low temperature activity of the catalysts,the introduction of the two rare earth elements can produce a certain inhibition effect,and the activity of the two doped catalysts decreased by about 5%at 280℃.XRD,BET,UV-Vis-NIR and H₂-TPR were used to characterize the structure,oxidation-reduction ability and species content of the catalyst,the characterization results can reasonably explain the performance changes of the catalyst before and after doping.The redox performance of Ce and Pr doped Fe/beta catalysts is an important factor affecting their catalytic activity.The redox performance of the catalysts is an important factor affecting their catalytic activity.The H₂-TPR characterization results of Ce and Pr doped Fe/beta catalysts show that the reduction peak positions of their high temperature active species（oligomeric Fe oxides）are increased by 46℃and 74℃respectively compared with those before doping,which leads to their better high temperature activity.