Preparation And Properties Of Tourmaline-containing MnCeO_x Core-shell Structure Catalysts For Low Temperature Selective Catalytic Reduction

A series of manganese-cerium composite oxide materials with a core-shell structure and tourmaline/manganese-cerium oxide composites were prepared by hydrothermal method and then characterized by X-ray diffractometer（XRD）,scanning electron microscope（SEM）,transmission electrons microscope（TEM）,N₂ adsorption-desorption,hydrogen temperature programmed reduction（H₂-TPR）,X-ray photoelectron spectroscopy（XPS）,in situ diffuse reflectance infrared fourier transform spectroscopy（in situ DRIFTS）and activity tests to characterise the crystal structure,morphology and redox properties of composites and further study the denitrification mechanism of catalysts.A series of manganese-cerium oxide composites were prepared.The preparations of solvent type,hydrothermal temperatures,hydrothermal time and the effects of manganese-cerium ratio on the structure and catalytic properties of the composites were investigated.It was found that when ethylene glycol and isopropanol were used at the volume ratio is 1:1,the hydrothermal temperature is 180°C,the hydrothermal time is 24 h,and the molar ratio of manganese to cerium is 4:6.The prepared catalyst（M4C6）is spherical with a core-shell structure,with the particle size about 1μm,the thickness of the shell is 100 nm,and the material has the best denitration performance,which can achieve more than 80%nitrogen oxide conversion at 110-230°C.In order to further enhance the low temperature denitration performance of the catalyst,The addition of tourmaline effects on the morphology and catalytic properties of the materials were investigated.The addition of tourmaline enhanced redox ability and increased the concentration of surface Mn⁴⁺,Ce³⁺and O_αof catalyst.When the tourmaline is added at an amount of 2%,the shell thickness of the catalyst（MCT2）is reduced to 50 nm.The catalyst can achieve a NO_x conversion of more than 80%at 105-230°C and can maintained 100%at140-200°C.M4C6 follows E-R mechanism well MCT2 follows both E-R and L-H mechanism.The addition of tourmaline promoted the conversion of NO to NO₂.The NO_x species are mainly in the form of bidentate nitrate.The reaction reacts as“fast SCR”,which is beneficial to the low temperature denitration reaction.