Particle Morphology Control Of MnO_x-CeO₂Composed Oxide Catalyst Prepared By Supercritical Antisolvent Process

Nowadays, nitrogen oxides emitted by stationary sources contribute up to nearly48%to total (NOx) emissions therefore being an important source for air pollution(e.g. ozone depletion, photochemical smog, greenhouse effects and acid rain). Themost effective technology to remove them is the selective catalytic reduction (SCR) ofNO by ammonia (4NO+4NH3+O24N2+6H2O). In recent years, low-temperatureSCR process is paid more and more attention due to its low energy and running cost.Manganese-cerium composite oxide (MnOx-CeO2) is one of the catalysts with goodlow-temperature activity. The nano-catalysts prepared with supercritical anti-solvent(SAS) technology exhibit the characteristic of narrow distribution and small particlesize Our group prepared manganese-cerium composite oxide via SAS process andobtained the special hollow nanospheres catalyst, exhibitingt high oxygen storagecapacity (OSC) and relatively good low catalytic activity. But the formation of lots ofsolid bridges and serious reunion among the groups of particles and low surface area,which is often takes place in preparing oxide particles via SAS technology, alsoappear in the process of preparing MnOx-CeO2. On the basis of previous work,preparing inorganic oxide particles with surfactant via SAS process is explored. wealso tried to prepare MnOx-CeO2nanospheres catalyst with better dispersion andhigher surface area and investigated the structure and the low-temperature SCRcatalytic performance in this study.We selected Suitable surfactants,PVP and P123, via experiments and appliedthem to prepare MnOx-CeO2catalysts via SAS process. The MnOx-CeO2nanoparticles, whose particle dispersion and specific surface got a better improvement,were successfully prepared. Investigations on the effects of the SAS processparameters showed that effectively controlling the particle morphology, particle size,particle dispersion and the specific surface area is possible by changingtemperature,pressure, and the mass ratio of surfactant and salt and otherparameters. Ultimately, wesuccessfully synthesized well-dispersed MnOx-CeO2composite oxide catalyst withhigh surface area.A Study on the samples prepared by PVP and P123assisted revealed that thesample prepared by surfactants assisted increase the oxygen vacancies and improvethe migration properties of the lattice oxygen, which is contributed to improve theoxidative capacity. The SCR catalytic performance of MnOx-CeO2nanospheresprepared by PVP assisted is better than that prepare by P123assisted, which is mainly due to the relatively larger specific surface area (79.35m2/g), more moderate surfaceMn2p binding and Mn/Ce ratio, more surface oxygen species, higher reducibility andbetter oxygen activation capability.The specific surface areas of MnOx-CeO2composite oxide catalyst prepared byPVP assisted increases with increasingMn content. Higher Mn content favors theformation of Mn species with higher oxidation state. The catalyst with a moderateMn/Ce ratio of4/4possesses a moderate binding energy of Mn2p, a moderate surfaceMn/Ce atomic ratio, and the best redox property, as a result showing the highestcatalytic activity for SCR reaction.