Preparation Of Ceria Nanodispersions And Study On Its Catalytic Performance

In recent years,Ce O₂ has attracted extensive attention because of its excellent oxygen storage capacity,unique Ce⁴⁺/Ce³⁺redox cycle properties and high catalytic activity.The surface of Ce O₂ nanoparticles possesses numerous active centers and defects,which plays an important role in the adsorption,charge transfer and chemical reaction of reactant molecules.However,Ce O₂ nanoparticles are easy to agglomerate during preparation and storage because of their high surface energy,which affects their physicochemical properties and catalytic performance.Thus,how to prepare Ce O₂ nanocatalysts with good dispersion and excellent performance has always been a research hotspot.Herein,we employ chemical precipitation method to modify the surface of Ce O₂nanoparticles,and the as-prepare Ce O₂ nanoparticles with different morphologies and particle sizes can disperse into solvents of different polarity.The effects of temperature,p H value,reaction solvent,surface modifier and other parameters on the synthesis process of Ce O₂nanoparticles were investigated.The photocatalytic performance of hydrophilic Ce O₂ nanoparticles for glyphosate degradation was investigated,and the activity of hydrophobic Ce O₂ nanoparticles for cyanosilylation reaction was explored.The main research contents of this paper are as follows:1.Hydrophilic Ce O₂ nanoparticles were prepared by chemical precipitation method with citric acid as modifier.Ce O₂ nanoparticles with particle sizes of 2.1,3.5 and 4.8 nm were obtained by adjusting the addition time of citric acid.The obtained Ce O₂ nanoparticles with various particle sizes were applied in the photocatalytic degradation of glyphosate.Ce O₂ nanoparticles of 2.1 nm exhibited the best photocatalytic performance,which can photodegrade glyphosate in 5 min and 20 min at p H=4 under UV and visible light respectively.2.1 nm Ce O₂ nanoparticles had 6 times（UV）and 20 times（visible light）degradation rates of 4.8 nm counterparts,and their degradation kinetic data accord with the pseudo first-order kinetic model.Meanwhile,the glyphosate adsorption capacity of 2.1 nm Ce O₂ nanoparticles decreased from 59.4 mg/g to 10.2 mg/g with the increase of p H value from 3 to 10.Ce O₂ nanoparticles can generate·OH and·O^2-radicals under ultraviolet and visible light irradiation.The experiment demonstrated that the strong oxidizing substance h⁺played a dominant role in the photodegradation of PMG.The C-N bond of glyphosate was attacked by the active species during the photocatalytic process,and glyphosate was degradated into aminomethyl phosphoric acid and other short chain acids.2.Hydrophobic Ce O₂ nanoparticles were prepared by chemical precipitation method with sodium laurate as modifier.The morphology and particle size of Ce O₂ nanoparticles can be adjusted by altering p H value,solvent,temperature,cerium source and other experimental conditions.Polyhedron-shaped Ce O₂ nanoparticles with sizes of 4 and 10nm,rod-shaped and spindle-shaped Ce O₂ nanoparticles were prepared.Among the various as-prepared Ce O₂ nanoparticles,10 nm polyhedron-shaped Ce O₂ nanoparticles with strong Lewis/Br?nsted acidic sites exhibited the highest catalytic performance for the cyanosilylation reaction.The yield of cyanosilylation reaction can achieve over 99%in 1h in heptane,and 0.75 h under solvent-free conditions.Meanwhile,the cyanosilylation reaction catalysed by Ce O₂ nanoparticles can still achieve a high yield of over 98%within 1 h in the 5th cycle,indicating an outstanding recyclability.The DFT calculation demonstrated that sodium laurate grafted on the surface of Ce O₂ nanoparticles can suppress the adsorption of HCN on the active sites of the catalysts and accelerate the cyanosilylation reaction.