Preparation Of Iron Based Catalysts And Their Application In The Elimination Of Atmospheric Molecular Pollutants

Rapid development of industry brings us not only the modem civilization,but also inevitably environmental pollution.Emission of harmful gases such as CO and NOx et al.mainly from the burning of fossil fuels(coal and oil)during the work time of coal fired power plant and motor vehicle,which course serious influence on atmospheric environment.Take into account that the energy structure dominated by coal and oil will not change in a short time,and fossil fuels will still play an irreplaceable role in the process of energy structure transformation in the next few decades.So,it is important for us to focus on the control of emissions from fossil fuels combustion.Catalysts used in motor vehicle exhaust are usually "three way catalyst" with precious metals,which is expensive and easy deactivation.The shortcomings of narrow reactivity window,poor selectivity in high temperature and toxic of V2O5 from V2O5-WO3(Moo3)/Ti02 used in coal-fired power plant also limited its application.As a result,more and more attentions are transferred to the development of nontoxic,cheap,non-noble metal catalysts with high catalytic performance.In this work,with the purpose of catalytic elimination of CO molecular from motor vehicle exhaust and NOx pollutants from coal-fired power plant,Fe2O3 was selected as the main active ingredients in the as designed catalysts.Kinds of Fe-based catalysts are wanted to be developed to meet the specific requirement of different model reaction.With the help of various characteristic instruments,physicochemical properties of the catalysts were in-depth understanding."Structure-activity relationship" and the reaction mechanism were well studied at the same time.The details about our research as follows:(1)Influence of impregnation sequence on the structure properties and dispersion state of the active species in FeCe/Al catalysts were investigated.And the role of Fe2O3 with different existence state was studied in the CO+O2 model reaction.We can find that,the existence state of Fe2O3 and CeO2 species will not be affected by changing the preparation methods.Fe2O3 present in the following forms:isolated Fe3+in tetrahedron sites,clusters in octahedral sites and iron ions in ceria lattice.The addition of CeO2 was beneficial to the dispersion of iron cations,and the amount of isolated Fe3+ follows:Fe/Al<FeCe/Al-CI<FeCe/Al-SI.To identity the iron species in the catalysts,we treated the as-synthesized catalysts by HNO3 solution.It was found that the cluster Fe3+ species was the main active species for CO+O2 reaction.As a results,FeCe/Al-CI got better catalytic performance than FeCe/Al-SI.Although the amount of cluster Fe3+ species of Fe/Al was the largest,the lack of Fe-O-Ce structure and lower content of Ce3+,surface oxygen species and Fe2+ made it the worst CO conversion.(2)Fe9M1Ox(M=Ti4+,Ce3+/4+,Al3+)catalysts were prepared by doping representative cations with different acid and redox properties.The physicochemical properties of obtained catalysts were systematically characterized through various technologies.The interactions of foreign reducible cations with Fe3+ lead to higher ratio of surface oxygen species and Fe2+ species,and also enhanced reaucibility at low temperature.Ti4+ doped re9Ti1Ox catalyst exhibited better catalytic performance than Fe9Ce1Ox and Fe9Al1Ox,which could be ascribed to the appropriate regulation of redox and acid properties of Ti4+ for Fe2O3.Fe9Ti1Ox showed a pronounced approximate 80%NOx conversion and remained stable in the coexistence of SO2 and H2O at 250? for 80 h,which could be used as a proper candidate of NH3-SCR catalysts.(3)Based on the work of part ?,a series of WO3/FeTiOx catalysts were prepared by impregnating WO3 species onto FeTiOx support.It can be found that the catalysts showed enhanced catalytic activity,widened operation temperature window and better SO2 durability.The addition of W03 species can not only increase the amount of surface acidity and active oxygen species,but also inhibit the redox ability of FeTiOx,weaken the interaction of Fe-O-Ti and decrease the generation of Fe2+.The suppression of nonselective NH3 oxidation effectively resulting in the enhanced high temperature activity.Through the coordinated control of surface acidity and reducibility,the high temperature activity of WO3/FeTiOx catalysts were improved and the operation temperature window was widened,which made it more practical in real use.