Cerium Oxide Nanowires Supported Palladium Catalyst For Photothermal Catalytic Oxidation Of Carbon Monoxide

CO is a toxic and harmful gas,colorless and odorless.It is easy to combine with human hemoglobin,causing insufficient oxygen supply and suffocating death.Compared with chemical reactions,the direct oxidation of CO to CO₂ is the simplest and most effective method.The CO oxidation method usually adopts the thermal catalysis.However,thermal catalysis is usually carried out at high temperature and consumes a lot of energy.At high temperatures,it is easy to cause the sintering of noble metals,which reduces the catalytic activity.Therefore,finding a method with high catalytic efficiency,good durability and low energy consumption is of great significance to promote the elimination of low energy consumption CO.Solar energy has attracted the attention of researchers because of its non-polluting and inexhaustible characteristics.Therefore,the conversion of solar energy to chemical energy is considered to be one of the important means to solve global energy and environmental problems.This paper combines photo and thermal to synthesize photothermal catalysts with photothermal response to achieve photothermal low-temperature CO oxidation.This thesis takes the use of photo and thermal to efficiently catalyze the oxidation of CO as the research goal,and selects CeO₂ which as a semiconductor material with high oxygen storage and release capacity and oxygen transfer capacity as the main catalyst,and supports Pd on CeO₂ to improve its catalytic performance.Study the effects of photo and thermal on the catalytic oxidation of CO reaction,and explore the reasons for the reaction results and the reaction mechanism,and are committed to solving the scientific problems of high energy consumption of CO oxidation and easy sintering of catalysts at high temperatures.The specific work is as follows:（1）CeO₂ as a support was first synthesized by hydrothermal method,and PdO/CeO₂ catalyst was prepared by loading Pd on the CeO₂ support by the deposition precipitation method.Through the photothermal CO oxidation activity test,it was found that the two catalysts have strong response to light.Through optimization experiments to explore the optimal loading of Pd,it is found that when the amount of Pd is 1.5 wt.%,the response of the catalyst to light is the most obvious.After adjusting the light intensity,it was found that as the light intensity continues to increase,the conversion temperature is also constantly decreasing.When the light intensity is 700 m W/cm~2,the T₅₀ of the 1.5PdO/CeO₂ catalyst is 48.8℃,through XPS test analysis,it was found that Pd exists in the form of PdO_x and metal Pd in 1.5PdO/CeO₂.Through EPR analysis,it was found that there are superoxide radicals and hydroxyl radicals in the photothermal CO oxidation process,which indicates that electron-hole pairs are generated in the photocatalytic reaction.When the sacrificial agent is added to the catalyst,it was found that the photothermal CO oxidation performance of the catalyst has been significantly reduced,which indicates that the generated electron-hole pairs play a major catalytic role in the catalytic reaction.The activation energy calculation shows that the activation energy is 64.6 kJ/mol under the dark reaction and 44.8 kJ/mol under the light condition,which was significantly reduced.The catalyst activity is tested by adding filters with different cut-off wavelengths at the xenon lamp.It shows that with the increase of the cut-off wavelength,the photothermal CO oxidation performance of the catalyst gradually decreases,which matches the UV-vis spectrum of the catalyst.In order to explore the reasons for the good catalytic activity and the role of PdO_x and metal Pd in the photothermal catalytic reaction,commercial P25 Ti O₂and Al₂O₃ were used as supports,and 1.5PdO/P25 Ti O₂and 1.5PdO/Al₂O₃ were prepared by the same method.Through the photothermal CO oxidation test,it was found that PdO_x,CeO₂ and metal Pd worked together.Among them,CeO₂acts as a semiconductor,when light hits the surface of the catalyst,electrons-holes are generated,which participate in the reaction to promote the reaction.When light hits the metal Pd surface,hot electrons will be generated on the metal Pd surface to generate a local plasmon resonance effect,which will cause local high temperature and promote the progress of the reaction.（2）In order to further explore the effects of catalysts prepared by different pretreatment methods on the photothermal CO oxidation performance,the same preparation method as 1.5PdO/CeO₂ was used to obtain 1.5Pd/CeO₂,1.5Pd/P25 Ti O₂,and 1.5Pd/Al₂O₃ by processing under reducing conditions.According to the catalyst activity characterization,the activity of the catalyst after reduction treatment is higher than that of the catalyst without reduction treatment.The analysis results of CA and electrochemical impedance spectroscopy test show that,compared with CeO₂,the1.5Pd/CeO₂ catalyst exhibits better charge transport efficiency and electron-hole separation efficiency,indicating that the 1.5Pd/CeO₂ catalyst is more helpful for the progress of the photothermal CO catalytic oxidation reaction.The activity test of the1.5Pd/P25 Ti O₂ and 1.5Pd/Al₂O₃ catalysts shows that in comparison with the1.5Pd/CeO₂ catalyst,CeO₂,PdO_x and metal Pd play a catalytic role in the photothermal catalytic reaction process.Among them,CeO₂ used as semiconductors.When light hits the surface of the catalyst,electron-holes are generated,and the metal Pd generates hot electrons,which increases the local temperature,thereby promoting the progress of the reaction.