Preparation Of Nickel Foam Supported Cerium-Based Monolithic Catalysts And Their Photothermocatalytic Performance For Degradation Of VOCs

In recent years,the pollution of volatile organic compounds（VOCs）caused by industrial waste gas and indoor decoration has become increasingly serious,which not only causes serious harm to human health,but also limits the rapid development of China’s economy to a certain extent.Therefore,developing new materials for efficient degradation of VOCs and developing new processes for effective purification of VOCs have practical significance for improving air quality in China.In this paper,based on the physical and chemical properties of materials and catalytic reaction mechanism,some foam nickel supported cerium oxide（CeO₂）based monolithic catalysts were designed,and the photo thermal synergistic catalytic purification of formaldehyde,toluene and other volatile organic compounds at room temperature was studied.By optimizing the reaction process and exploring the reaction mechanism,important research foundations and theoretical data are provided for the research direction of photothermal synergistic purification of VOCs.Firstly,the reduced graphene oxide（rGO）coating and CeO₂nanosheets were grown on the three-dimensional porous nickel foam（NF）metal substrate by a two-step hydrothermal method to construct a monolithic catalyst with NF as the carrier and rGO and CeO₂coated on the surface.The three-dimensional pore structure of NF is not only conducive to mass and heat transfer,but also avoids the agglomeration of the catalyst,so that the active component CeO₂exposes more active sites.The rGO and NF with good photothermal effect convert solar energy into heat energy efficiently,increase the surface temperature and activate the lattice oxygen of CeO₂,and then drive them to achieve efficient degradation of formaldehyde and toluene at room temperature.The experimental results showed that the CeO₂-rGO-NF metal-based monolithic catalyst synthesized by in-situ hydrothermal method could degrade 300 ppm formaldehyde in the batch reactor to 15 ppm within 20 minutes under xenon lamp illumination.In the flow reactor,500 ppm formaldehyde can be completely degraded within 10 minutes（>95%）.Compared with hydrothermally synthesized CeO₂,CeO₂-NF and impregnation synthesized CeO₂/NF,CeO₂/rGO/MS based on melamine sponge（MS）substrate,CeO₂-rGO-NF exhibited significantly enhanced formaldehyde and toluene removal performance.The experimental results under different wavelength light sources confirm that near-infrared radiation（NIR）plays an important role in the photothermal conversion process.The irradiation of NIR light source can increase the surface temperature of the catalyst to～140℃.The catalytic process of VOCs on CeO₂-rGO-NF can be explained by the Mars-van Krevelen mechanism.Under the temperature condition of lattice oxygen activation,the surface lattice oxygen produces electron transfer with the excited activated oxygen through the action of oxygen holes,and realizes the efficient oxidation of VOCs.Secondly,the noble metal Pt modified ceria supported monolithic catalyst（Pt-CeO₂-NF）was prepared by simple in-situ hydrothermal method and sodium borohydride reduction method.The strong plasma effect of Pt within the full spectrum range and the charge transition between Pt and CeO₂enhance the photothermal effect of the monolithic catalyst,and uniformly increase the surface temperature of the Pt-CeO₂-NF composite（the surface temperature reaches～173℃within 3 minutes of illumination）,thereby driving the thermocatalytic reaction of the catalyst.Through the close combination between Pt and CeO₂,the metal-support interaction not only activates the lattice oxygen of CeO₂,but also further increases the concentration of surface oxygen vacancies,thereby accelerating the oxidation cycle of gaseous oxygen on the catalyst surface and achieving efficient removal of toluene.Cycle experiments and durability experiments show that the Pt modified monolithic catalyst has good stability and reusability.During the water resistance test,it was found that low concentration of water vapor（3 vol%,5vol%）promoted the catalytic degradation of toluene by Pt-CeO₂-NF,while high concentration of water vapor（15 vol%）inhibited it.Finally,the important reaction groups on the catalyst surface were identified by in-situ infrared diffuse reflectance spectroscopy,and the intermediate reaction products of toluene on the catalyst surface were analyzed by gas chromatography-mass spectrometry（GC-MS）.The mechanism of photocatalytic oxidation elimination of toluene on the catalyst surface was proposed.