Formaldehyde Oxidation Performance And Mechanism Study Of Noble Metal Decorated Hierarchical Catalysts

Formaldehyde is considered a major indoor air pollutant,and long-term exposure to high-concentration formaldehyde can cause serious health problems to human bodies.Therefore,it is necessary to reduce formaldehyde concentration in the air.Among the formaldehyde removal techniques,catalytic oxidation at room temperature is the most promising method,which can completely decompose formaldehyde into water（H₂O）and carbon dioxide（CO₂）without other energy input.Supported noble metal catalysts have received widespread attention due to their excellent performance towards room-temperature formaldehyde oxidation.However,the preparation of supported noble metal catalysts with low loading and high efficiency is still challenging.In this paper,noble-metal efficiency and catalytic performance of the catalyst can be improved by using hierarchical supports,introducing surface active oxygen species,and combining adsorption and photocatalysis with room-temperature catalytic oxidation.The main research contents are as follows:To investigate the critical role of platinum（Pt）and gold（Au）in catalytic formaldehyde oxidation,Pt-Au/Ti O₂ catalysts are synthesized by co-depositing Pt and Au on Ti O₂.On the one hand,Au nanoparticles can rapidly activate the lattice oxygen on the Ti O₂ surface to oxidize formaldehyde into dioxymethylene（DOM）.On the other hand,negatively charged Pt can effectively adsorb and activate oxygen（O₂）in air,oxidizing DOM into formate species and eventually to H₂O and CO₂.This synergy can achieve the rapid decomposition of formaldehyde on the supported Pt-Au/Ti O₂ catalyst.To improve the utilization efficiency of Pt,we use Mn O₂ nanosheets grown on three-dimensional carbon foam as the support for Pt nanoparticles.The three-dimensional hierarchical porous structure of the support promotes the uniform deposition of Pt nanoparticles and fast diffusion of gas reactants.Carbon foam can quickly adsorb and reduce formaldehyde concentration in the air,and the active lattice oxygen on Mn O₂ surface and activated O₂ on Pt can completely oxidize the adsorbed formaldehyde.The combination of adsorption and oxidation can achieve the rapid removal and oxidative decomposition of formaldehyde.To prove the critical role of surface-active oxygens,we use Co₃O₄-Ni O composite oxides with abundant surface-active oxygen as the support for Pt.Numerous active oxygen atoms at the Co₃O₄ and Ni O interface and oxygen vacancies derived from the reduction process can efficiently adsorb formaldehyde and convert it into DOM.Electrons transferred from NiO to Pt can enhance the adsorption and activation of O₂ on Pt nanoparticles,promoting the further oxidation of DOM to formate and CO₂.Moreover,the hierarchical hollow structure of the Co₃O₄-Ni O is conducive to providing highly exposed Pt active sites.To improve the activity of surface oxygen and Pt nanoparticles,we combine photocatalytic oxidation with room-temperature catalytic oxidation using Pt/Bi₂Mo O₆microspheres as the catalyst.Under visible light irradiation,photo-generated holes can improve the activity of surface oxygen species,effectively oxidizing formaldehyde into DOM and formate.The transfer of photo-generated electrons from the conduction band of Bi₂Mo O₆ to Pt nanoparticles can enhance the adsorption and activation of O₂ by Pt,favoring the complete decomposition of formate to CO₂.On the other hand,Pt nanoparticles can promote the charge separation efficiency of Bi₂Mo O₆.Through the above strategies,we successfully prepared noble-metal-based hierarchical catalysts with low loadings and high efficiency.The properties of the catalysts and the mechanism of performance improvement were systematically analyzed.Therefore,this paper provides significant information for the preparation and application of highly efficient and stable noble-metal-deposited hierarchical catalysts.