Application Of Two-dimensional Cerium Oxide-based Composite Catalytic Materials In The Purification Of VOCs

Volatile organic compounds（VOCs）emitted from industrial production are an important class of air pollutants.As emission standards become more and more stringent,reducing VOCs emissions is a very important issue in the environmental field.A variety of technologies for the removal of VOCs have been developed.Catalytic oxidation is considered to be one of the most important and promising methods due to its high catalytic oxidation efficiency for VOCs,especially the conversion of VOCs into harmless CO₂ and H₂O.In order to obtain excellent catalytic performance,various well-designed graded catalysts have been manufactured in recent years.Due to its redox properties,ceria-based materials have large oxygen storage and release capabilities,which makes them an excellent candidate for catalysts for the oxidation of volatile organic compounds（VOCs）.Therefore,in this paper,camellia petals and lettuce leaves were used as biological templates to prepare two-dimensional cerium oxide-based composite materials with hierarchical porosity,and formaldehyde was used as a model pollutant to explore the effect of the material ratio,structure and properties of the composite catalyst on the catalytic performance of formaldehyde.The main contents are as follows:（1）The two-dimensional cerium oxide composite copper oxide catalyst prepared by using camellia petals as a biological template has a layered multi-level porous structure with a bionic morphology and good catalytic effect.The research results show that when the copper-cerium material ratio is 1:9,Cu O can be completely dissolved in the CeO₂ crystal lattice to form a copper-cerium solid solution with a cubic fluorite structure,and the grain size is small.The catalyst has an ultra-thin sheet structure and developed mesoporous structure,uniform pore diameter and large specific surface area,which is beneficial to improve its catalytic activity.In the study of the catalytic oxidation performance of the copper-cerium composite catalyst on formaldehyde,it is found that the catalyst with a copper-cerium material ratio of 1:9 has the best redox performance.The highly dispersed copper oxide on the catalyst surface and the cerium oxide support have a strong interaction at 225°C.At this time,the conversion rate of catalytic oxidation of formaldehyde can reach 100%.（2）A two-dimensional cerium oxide composite zirconia catalyst was prepared by using lettuce leaves as a biological template.The research results show that the zirconium-cerium composite catalyst retains the microscopic morphology of the original template and has a thin layer structure.When the material ratio is 1:9,2:8,and5:5,there is no ZrO₂ diffraction peak in the catalyst,that is,Zr⁴⁺enters the cerium oxide After the crystal lattice,a solid solution of cerium and zirconium can be effectively formed to generate more oxygen vacancies.In addition,the addition of zirconium can make the cubic fluorite structure of ceria more stable and help increase the specific surface area of the composite catalyst.When the ratio of cerium to zirconium is 5:5,the relative concentration of Ce³⁺on the catalyst surface is the highest,it has better oxygen transfer ability,and has the best catalytic activity to formaldehyde.The conversion rate of catalytic oxidation of formaldehyde can reach 100%at 325℃.（3）A two-dimensional copper-zirconium-cerium three-phase catalyst was prepared by using lettuce as a biological template.The research results show that the copper-zirconium-cerium catalyst retains the microscopic morphology of the original template.When the copper-zirconium-cerium material ratio is 1:1:4,1:1:8,there is no diffraction peak of Cu O and ZrO₂,indicating that Cu²⁺and Zr⁴⁺ions have entered the CeO₂ lattice to form a good solid solution.In addition,when the copper-cerium-zirconium material ratio is 1:1:8,the average crystal grain size of the catalyst is the smallest,only 2.5 nm.Cu²⁺,Cu⁺,Ce³⁺,Ce⁴⁺,Zr⁴⁺ions coexist on the surface of the copper-cerium-zirconium catalyst.When the material ratio is 1:1:8,the relative content of Ce³⁺is the highest.more oxygen vacancies and unsaturated chemical bonds will be formed on the surface of the Cu O-ZrO₂-CeO₂ catalyst,so more oxygen will migrate from the main body to the surface of the catalyst,which will help improve its catalytic activity.The conversion rate of oxidized formaldehyde can reach 100%.