Fabrication Of Cordierite Monolithic Catalyst With Single/double Layercoatings And Studies On The NH₃-SCO

With the acceleration of industrialization and improvement of living standard,the emissions of NH₃ from fixed and mobile sources become increasingly pronounced.NH₃,as a toxic and harmful odor pollutant,does harm to human health and natural environment.Therefore,the removal of NH₃ in tail gas is an urgent and necessary work.In numerous NH₃ removal techniques,ammonia selective catalytic oxidation technology is efficient and eco-friendly to attract wide spread attention.Cordierite monolithic catalyst has high mass transfer efficiency,low bed pressure drop,small amplification effect and simplicity for regeneration.In addition,the molecular sieve catalyst modified by metal has good hydrothennal stability.Cu-based catalyst has become the research focus because of its low cost and predominant performance for the ammonia catalytic oxidation.Based on the above research results,the composite metal oxide catalysts?CuO-Fe₂O₃,CuO-CeO₂,CuO-Co₃O₄?and the molecular sieve catalyst modified by metal?Cu/ZSM-5,Cu/beta,Fe/ZSM-5,Fe/beta?were prepared in this study.Forementioned catalysts as the active component were coated on the surface of cordierite honeycomb ceramics carrier channel.Cordierite monolithic catalyst with single or double layer?lining for composite metal oxides,outer layer for the modified molecular sieve?was prepared by the coating method.A Series of catalysts were investigated for the NH₃-SCO catalytic performance and characterized by XRD,H2-TPR and SEM.Researches show that cordierite monolithic catalysts with single coating?CuO-Fe₂O₃,CuO-CeO₂,CuO-Co₃O₄?displayed favourable performance in ammonia catalytic oxidation,but the N2 selectivity of these catalysts was poor.The cordierite monolithic catalysts with single coating of modified molecular sieve?Cu/ZSM-5,Cu/beta,Fe/ZSM-5,Fe/beta?presented the excellent N2 selectivity,but the activity of the series catalysts was poor.Considering that composite metal oxide catalysts exhibited the favourable activity but inferior N2 selectivity while the molecular sieve catalyst modified by metal displayed the bad activity but superior N2 selectivity,the cordierite monolithic catalyst with double coating?lining for composite metal oxides,outer layer for the modified molecular sieve?was prepared.The results showed that the cordierite monolithic catalyst with double coating could combine the advantages and abandon the disadvantages of both composite metal oxide catalysts and the molecular sieve catalysts.The double coating catalysts showed the excellent activity and N2 selectivity.The NH₃ conversion was nearly 100%at 350 ? and N2 selectivity was about 90%in the temperature range.For the double coating catalysts,internal coating?composite metal oxides?was critical to the catalytic activity of the catalysts and the outer coating?modified molecular sieve?determined the N2 selectivity of the catalysts.The rational design of the catalysts achieved the purpose of the synergistic catalytic oxidation of NH₃ and made this kind of cordierite monolithic catalyst with coatings potential in the industrial application.