Crystal Plane Regulation And Photocatalytic Properties Of Ce-based Composite Oxides

Excessive emission of nitrogen oxides into the atmosphere is the main cause of acid rain,haze and photochemical pollution.At present,there are many methods for the treatment of nitrogen oxides especially the selective catalytic reduction technology?SCR?.The most widely used catalyst of this way for commerce is V₂O₅WO₃/TiO₂ which has the disadvantages like narrow active temperature range,easy deactivation,toxicity of V₂O₅and secondary pollution of the environment.Therefore,the development of environmentally friendly and highly active catalysts is the main research direction.Cerium has received extensive attention due to its high oxygen storage/release capacity,empty d electron orbit and excellent redox performance whereas commercial cerium oxide has low catalytic activity.It has been found that high active crystal face exposure can effectively improve the photocatalytic activity of materials.The redox properties and stability of materials with CeO₂ and other transition metals can be significantly improved.Therefore,this thesis mainly studies the preparation of cerium oxide-based composite nanomaterials with high catalytic activity and exposed high active crystal faces with low reduction temperature.In this thesis,hydrothermal method was used to prepare CeO₂,Titanium and Cerium,Cobalt and Cerium composite oxides with high active crystal surfaces via crystal surface regulation.XRD,SEM,TEM,XPS,UV-vis,H₂-TPR and photothermal catalytic denitrification were used to characterize the structure and properties of materials.The main findings are as follows:1 CeO₂ nanomaterials with different morphologies and crystal surfaces were prepared by hydrothermal method at different NaOH concentration and hydrothermal temperature.The results show that in hydrothermal state at 120?,the formation of granular CeO₂exposed to low activity?111?surface under low concentration of NaOH;the formation of CeO₂ nanorods exposed to high activity?220?and?200?surface under high concentration of NaOH.Nanocubes exposed to highly active?200?faces are formed at 180?.Compared with nanocubic structures,CeO₂ nanorods have a larger specific surface area(94 m²·g^-1)and a smaller band gap?2.95 eV?,which have better reduction and higher catalytic efficiency.2 Titanium Cerium composite oxide nanocatalysts with high activity exposed to CeO₂?200?and?220?crystal faces were prepared by hydrothermal method.The results show that the reduction ability and catalytic performance of the composite titanium catalyst are superior to those of pure CeO₂.A nanorod-like Titanium Cerium solid solution is formed,and composite oxide has good ultraviolet light absorbing ability,and the forbidden bandwidth is reduced to 2.81 eV.As the calcination temperature becomes high,the catalyst size increases,and the crystallinity increases.The photocatalytic performance of NO found that uncalcined sample with the concentration ratio of 1:5 had the best reduction performance,and the NO highest catalytic efficiency was 94%.3 A cobalt-cerium composite oxide nanocatalyst with exposed CeO₂ high activity crystal surface was prepared by the hydrothermal method.The results of the study showed a rod-like structure and exposed high activity?200?and?220?faces.The sample still exposed to the high active crystal face after the incorporation of cobalt,and the specific surface area was also large.Optical properties and reduction properties of the composite oxide are improved.The catalytic NO study found that the catalytic activity was enhanced after cobalt doping.The sample with cobalt to lanthanum ratio of 1:5 had the lowest reduction temperature and the highest catalytic activity.After calcination at 600?,the catalytic efficiency of NO was 99%.