| The MnOx-CeO2-TiO2 ternary composite catalysts have the advantages of high denitration performance,simple preparation method,green and easy to recycle,so they are the current research hotspot in the selective catalytical reduction of NOx with ammonia(NH3-SCR).However,the sulfur resistance of such catalysts needs to be further improved,which may be due to their relatively small mesopore size.In this paper,Mn-Ce-Ti-O composite aerogel catalysts with larger mesopore size were prepared by two methods.Their NH3-SCR performance and the water/SO2 resistance were investigated,which were related to their pore texture(pore size,pore volume and specific surface area),the numbers of acid sites and surface reducible species.Their possible NH3-SCR reaction mechanism was discussed.?.Novel Mn-Ce-Ti-O composite aerogels with large mesopore sizes were prepared by a one-pot sol-gel method using propylene oxide as a network gel inducer and ethyl acetoacetate as a complexing agent.The effect of the calcination temperature(400,500,600 and 700?)on their NH3-SCR performance was investigated.Results indicate that the Mn-Ce-Ti-O catalyst calcined at 600? exhibits the highest NH3-SCR activity and the lowest apparent activation energy due to its most abundant Lewis acid sites and best reducibility.The NO conversion of the MCTO-600 catalyst reaches 100%at 200? in the presence of 100 ppm SO2,showing the superior resistance to SO2 poisoning.This should be mainly attributed to its large mesopore size with an average pore size of 32 nm and abundant Lewis acid sites.The former fact facilitates the decomposition of NH4HSO4 while the latter reduces vapor pressure of NH3 The NH3-SCR process on the MCTO-600 catalyst follows both the Eley-Rideal(E-R)and Langmuir-Hinshelwood(L-H)mechanisms with the E-R mechanism being a dominant route.?.Another type of Mn-Ce-Ti-O composite aerogels were synthesized following the same routine above except that resorcinol(R)and furfural(F)were added into the precursors as a sacrificial template,which were polymerized in the sol-gel process and removed during calcination(400,500,600 and 700?)to obtain aRF-MCTO-x aerogels,where x denoted the calcination temperature.As a comparison,the aerogels were carbonized(400,500,600 and 700?)under nitrogen atmosphere to obtain nRF-MCTO-x,where x denoted the carbonization temperature.It is found that the nRF-MCTO-x aerogels have poor NO conversion efficiencies.For example,the nRF-MCTO-600 has only a denitration efficiency of 30%in the temperature range of 120-200?.However,the aRF-MCTO-x aerogels have excellent NH3-SCR performance.For example,the aRF-MCTO-500 achieves a NO conversion of more than 90%from 140 to 320? with a NO conversion of 100%from 160 to 300?.Further research reveals that the introduction of RF sacrificial template not only increases the specific surface area,pore volume and pore size of aRF-MCTO-x composite aerogels to a certain extent,but also reduces their grain size,and increases the numbers of surface acid sites and reducible species,which jointly promote their NH3-SCR performance at low temperatures.?.The SO2 resistance of the aRF-MCTO-500 and MCTO-500 is compared.It is found that the introduction of RF sacrificial template can improve the SO2 resistance of the catalysts.When 100 ppm SO2 was introduced for 6 h at 200?,the NO conversion efficiency remain at 100%for the aRF-MCTO-500 while that of the MCTO-500 is only 75%.This could be mainly ascribed to the larger average pore size of the aRF-MCTO-500(34 nm)than the MCTO-500(22 nm).XPS analysis of the poisoned catalysts reveals that the peak areas and intensities of the S 2p and N 1s orbits of the aRF-MCTO-500 are significantly lower than that of MCTO-500,indicating that the introduction of RF sacrificial template enhances the SO2 tolerance of the aRF-MCTO-500.Moreover,the ratios of Mn4+/(Mn4++Mn3++Mn2+)and O?/(O?+O?)on the surface of the aRF-MCTO-500 and MCTO-500 decrease to a certain extent after the SO2 poisoning test. |
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