Application Of Ceria‐Supported Single‐Atom Catalysts In Catalytic Reaction Of Volatile Organic Compounds Degradation

Volatile organic compounds（VOCs）come from a wide range of sources and have toxicity,carcinogenicity,mutagenicity and teratogenicity,which have an irreversible impact on the environment and human health.As a toxic aromatic VOCs,the production of toluene is closely related to human activities.Most of the toluene produced directly enters the ambient air,and a small part enters the water and soil through garbage and oil pollution.Therefore,it is urgent not only to control the emission of toluene at the source,but also to degrade toluene in nature.Low temperature（20-400℃）catalytic oxidation is considered to be one of the most effective and economical ways to remove toluene from industrial waste gas system because of its high degradation efficiency,low operation cost and green environmental protection of degradation products.In order to make catalytic oxidation more competitive economically,catalytic materials began to develop towards the direction of high performance and low reduction temperature,including catalytic materials loaded with precious metals and transition metal oxides began to enter people’s field of vision.Therefore,in this paper,lettuce leaves were used as biological templates to prepare two-dimensional ceria based monatomic catalyst materials with graded porosity.Toluene was used as a model pollutant to explore the effects of noble metal loading,structure and properties of monatomic catalyst on the catalytic performance of toluene.The main contents are as follows:（1）2-D ceria carrier materials with different precursor solution concentrations were prepared with cosmetic cotton,filter paper and lettuce leaves as templates.The ceria carrier material of lettuce leaf template has a layered and multistage porous structure with bionic morphology,and the morphology is less affected by the concentration of precursor solution.The results show that Ce O₂ carrier material with precursor solution concentration of 0.15mol/L has larger specific surface area,more oxygen vacancies and better reduction performance.Therefore,in the follow-up study,0.15 mol/L was used as the precursor solution concentration of ceria carrier.（2）2-D ceria based monatomic catalysts were prepared by using lettuce leaves as biological templates.The results show that the Au₁/Ce O₂ Catalyst replicates the microstructure of the original template and has a lamellar structure.There is no X-ray diffraction peak related to gold in the catalyst,and the dispersion of gold is suitable and the loading is low.In addition,the addition of gold species can promote the growth of ceria crystals.When the gold loading is 0.3 wt%,the content of Au⁰and Ce³⁺on the catalyst surface increases,which increases the number of oxygen vacancies.The interaction between Au and Ce O₂ leads to the weakening of Ce-O bond,improves the redox ability of oxygen species on the Ce O₂ surface,and forms more oxygen vacancies.The number of oxygen vacancies is relatively the largest,which improves the oxygen migration ability and promotes the reduction ability.The catalytic activity of toluene is the best,and the conversion of formaldehyde can reach 90%at 243℃.（3）2-D ceria loaded platinum monoatomic catalyst was prepared by using lettuce leaves as biological template.The results show that ceria loaded platinum monatomic catalyst retains the micro morphology of lettuce leaves and has a lamellar structure.There are no diffraction peaks related to platinum in the catalyst,which may be due to the low loading and high dispersion of platinum.In addition,when the platinum loading is 1wt%,the relative content of Ce³⁺on the catalyst surface is the highest.Due to the increase of Ce³⁺,the oxygen vacancy on the catalyst surface will increase,so more oxygen will migrate from the main body to the catalyst surface,which is conducive to improving its catalytic activity.The conversion of catalytic oxygenated toluene can reach 90%at 208℃.（4）Through the analysis of the intermediate products of toluene catalytic oxidation reaction,it is speculated that the adsorbed toluene molecules may be oxidized by the catalyst under the action of oxygen and surface active oxygen to produce benzaldehyde,benzyl alcohol and benzoic acid intermediates,and finally form CO₂ and H₂O.The reaction process conforms to Marsevan Krevelen mechanism.