Preparation Of CeMn/TiO₂ Catalyst By In-situ Growth Method And Study On Its Low-temperature SCR Denitrification Performance

In this paper,TiO₂ with stable properties was used as a catalyst carrier.In-situ growth method was used to control the growth of highly dispersed and high-valence manganese oxide as the active component,supported on the spherical carrier TiO₂.Then the impregnated cerium nitrate precursor was calcinated to prepare Ce?1.0?Mn/TiO₂-SP-300 catalyst.Characterization results were proved that cerium-manganese-titanium catalyst prepared by the in-situ growth method had high-valence and highly-dispersed active components,avoiding the uneven distribution of elements and low content Mn⁴⁺of the cerium-manganese-titanium catalyst prepared by the impregnation method,thereby having better catalytic performance.The Ce?1.0?Mn/TiO₂-SP-300 catalyst was prepared by in-situ growth method+impregnation and calcination,and the optimum catalyst preparation conditions?Mn,Ce content and calcination temperature?,process parameters?gas hourly space velocity?and their effect on the catalytic performance of their catalysts were investigated.The activity test results showed that when the calcination temperature was 300 ^oC,the suitable loading of Mn was 8 wt%,and the Ce/Mn molar ratio was 1.0,the Ce?1.0?Mn/TiO₂-SP-300 catalyst could maintain more than 90%NO conversion in the temperature range of 150-300 ^oC under gas hourly space velocity of 10500-27000 h^-1.The characterization results showed that the doped Ce Ox reduced the crystallinity of the active component manganese species?mainly Mn O₂?,and had little effect on the surface morphology of Ce?1.0?Mn/TiO₂-SP-300 catalyst,and it maintained a relatively regular morphology.During the reaction,Ce Ox doping could produce more Mn⁴⁺species and more adsorbed oxygen species,thereby improving the low-temperature SCR denitration performance.By comparing the denitration performance of catalysts prepared by traditional impregnation method and the physical and chemical properties of the catalyst prepared by different preparation methods,it was found that Ce?1.0?Mn/TiO₂ catalyst with the same Ce/Mn molar ratio prepared by different methods showed different element distribution,morphological structure,acid strength and thermal stability.The corresponding redox capacity and the content of metal oxides with different valences were also differ greatly.It was further found that the in-situ growth method can regulate the growth of high-dispersion and high-valence active components,the prepared Ce?1.0?Mn/TiO₂-SP-300 catalyst had a stable core-shell structure,rich acid sites,and excellent redox properties,abundant Mn⁴⁺species,a more diverse distribution of cerium oxide and strong manganese-cerium synergistic effect.It was speculated that the preparation advantage of the in-situ growth method was that the low-valence manganese ion adsorbed on the spherical carrier TiO₂ was oxidized into manganese dioxide in situ by the high-valence manganese,the more uniformly distributed manganese dioxide shell layer surrounded the carrier,thereby forming a core-shell structure.Because it was completed in a liquid-phase system at room temperature,avoiding the phenomenon of uneven dispersion of the active components after drying and calcination of traditional impregnation method.Therefore,the low temperature denitration performance of Ce?1.0?Mn/TiO₂-SP-300 catalyst was more excellent than Ce?1.0?Mn/TiO₂-IP-300 catalyst.The catalytic performance and stability of the catalysts prepared by the two methods in SO₂ atmosphere were studied.The results of the activity test founded that the NO conversion of Ce?1.0?Mn/TiO₂-IP-300 catalyst at 175 ^oC in 10500 h^-1 after 9 h stabilized at about 76%in 80 ppm SO₂ atmosphere,and the NO conversion of Ce?1.0?Mn/TiO₂-SP-300 catalyst finally stabilized at about 86%;the NO conversion of Ce?1.0?Mn/TiO₂-IP-300 catalyst at 200 ^oC decreased from 92%to 72%,and the NO conversion of Ce?1.0?Mn/TiO₂-SP-300 catalyst decreased from 100%to 90%,and finally stabilized at about 90%.This was because the core-shell structure of the fresh sample Ce?1.0?Mn/TiO₂-SP-300 catalyst protected the catalyst.The better distribution of Ce⁴⁺species and the stronger synergistic effect of manganese-cerium made it have better resistance to sulfur poisoning performance.The Ce?1.0?Mn/TiO₂-SP-300-W catalyst regenerated by water washing could recover most of the activity of fresh samples.All these indicate that Ce?1.0?Mn/TiO₂-SP-300 catalyst had great potential for industrial application.