Synthesis And Application Of Three-Dimensionally Ordered Macroporous Mixed Metal Oxide Catalysts For Removing NO_x From Marine Diesel Engine Exhaust

NOx emitted by marine diesel engine is a kind of gas that pollutes the environment seriously and endangers human health.The NH3 selective catalytic reduction of NOx technique has been identified as the well-known method for elimination of NOx because of its high activity,selectivity and low expense,The vanadium-based catalysts(V2O5 supported on TiO2,modified by WO3 or M0O3 oxide)have been commercial used since the 1970s,they displayed fairly good NH3-SCR performance at medium-high temperatures.However,this kind of classical formulation is facing major problems due to its narrow active temperature window.Moreover,the catalytic system was usually laid aside the upstream of the desulfurization and dust remover units to avoid the reheating of the catalyst owing to the high working temperature.As a result,the catalyst is readily covered by soot particles or unburned fuel from marine diesel engine exhaust,causing decreased catalytic activity.In this work,a series of three-dimensionally ordered macroporous mixed metal oxide catalysts(3DOM-MnFe1-δCoδOx and 3DOM-Fe10-xVx)were successfully prepared using PMMA nanospheres as hard template for removing NOx from marine diesel engine exhaust.These samples were characterized by XRD,N2-BET,H2-TPR,NH3-TPD,SEM,TEM,STEM-mapping,UV-vis,Raman,XPS and In situ DRIFT.DeNOx performance with H2O/SO2 and soot tolerance of these samples were evaluated.The results are as follows:(1)Boosting activity over cobalt doped 3DOM MnFeOx for low temperature SCR of NOx with NH3.Cobalt doped MnFeOx ternary oxides with 3DOM structure(3DOM-MnFe1-δCoδOx δ=0.2,0.4 and 0.6)were prepared via a simple hard template method.It was revealed that properly doping MnFeOx with cobalt oxide displayed better catalytic performance,the 3DOM-MnFe0.6Co0,4Ox catalysts displayed best low temperature activity for selective catalytic reduction of NOx with NH3,the NOx conversion reached above 80%between 90 to 343℃.Moreover,the introduction of cobalt could promote the reduction of Fe species,boost the ratio of surface Mn4+ and Fe3+ as well as the amount of the acid sites on the surface,these are the reasons for improving the catalytic performance of catalyst.Additionally,the 3DOM-MnFe0.6Co0.4Ox catalyst exhibited superior soot tolerance due to its special ordered architecture.We found that the soot had a reduction activity for NOx at high reaction temperature,which can effectively extend the active temperature window.Most importantly,3DOM-MnFe0.6Co0.4Ox displayed remarkable SO2 tolerance compared with un-modified 3DOM-MnFeOx catalyst.The in situ DRIFT spectra verified that L-H and E-R mechanisms might be simultaneously existed in the reaction and the doping of cobalt species could effectively decrease the formation rate of metal sulfates on the surfaces of 3DOM-MnFe0.6Co0.4Ox catalyst.(2)Three-dimensionally ordered macroporous Fe-V binary metal oxide catalyst for low temperature selective catalytic reduction of NOx from marine diesel engine exhaust.For the first time,a series of 3DOM-Fe10-xVx binary metal oxide catalysts with different Fe/V ratios were successfully prepared using PMMA nanospheres as hard template for removing NOx from marine diesel engine exhaust.The 3DOM-Fe10-xVx(x=0.5,1.0 and 1.5)binary metal oxide samples possessed high-quality 3DOM architecture,and exhibited better low-temperature activity than pure 3DOM-FeOx,3DOM-VOx and the conventional Fe10-xVx catalyst without macropores.Among them,the 3DOM-Fe9.0V1.0 showed excellent NH3-SCR performance with a wide active temperature window,achieving a NOx conversion higher than 80%between 220 to 412℃.The VOx modification effectively increased the surface adsorbed oxygen species,as well as the total acid amount over the 3DOM-Fe9.0V1.0 catalyst,there is synergy between Fe and V.In addition,the 3DOM-Fe9.0V1.0 catalyst exhibited high resistance to soot than Con-Fe9.0V1.0 due to its special space structure,it was also found that the soot could act as reductant to reduce NOx over 3DOM-Fe9.0V1.0 and eventually led to the improvement of the high-temperature deNOx performances.The L-H reaction pathway was determined to be the reaction mechanism at 150℃ and 250℃ and E-R mechanism also existed in the reaction at 250℃ from the results of the in situ DRIFTS analysis.