| The utilization of fossil fuels emits a large amount of volatile organic compounds(VOCs)and CO and other pollutants,which are extremely harmful to human health and the balance of the ecosystem.Catalytic elimination is one of the most effective strategy to control pollutants such as VOCs and CO.However,current catalysts face challenges such as high-cost,insufficient activity at low temperatures,and poor stability under actual working conditions.Therefore,the development of new generation catalysts with low metal loading as well as high catalytic activity has become widely investigated.Surface engineering and interface engineering are effective strategies for regulating catalytic active centers.On the one hand,the interface effect between the metal nanoparticle and the support is an effective strategy for constructing active sites and increasing the amount and types of surface-active sites;On the other hand,the optimized modification strategy of the surface structure/interface structure can modulate the geometric structure and electronic properties of the active site,further promoting the interaction between the reactants and essentially regulate the surface chemical properties of the catalyst(activated surface lattice oxygen,lattice distortion,redox properties,etc.).In this paper,oxygen vacancy control strategies,interface engineering and surface doping are used to control the properties of active sites.Propene(C3H6),propane(C3H8)and CO are used as model pollutants to investigate the performance of abricated Pt/TiO2 and Cu/TiO2 catalysts.The structureactivity relationship between surface properties(oxygen vacancies,surface/interface doping,interface electron transfer)and catalytic oxidation performance was also revealed.We further optimized the synthesize method to obtain a high-efficiency Cu1/TiO2 single-atom catalyst(SACs).By selecting Cu1/TiO2 SACs as a model catalyst,the dual activation mechanism of surface chemisorbed O2 and surface lattice oxygen was in-depth studied.Finally,the dual activated oxygen synergistically promoted low-temperature CO catalytic oxidation was elucidated.This work provides effective principle for the design of high-activity and high-stability catalysts.The main results obtained in the full text are as follows:1.This work aims to investigate the interaction between oxygen vacancies and Pt nanoparticles,and study its effect on the catalytic oxidation performance of C3H6 and C3H8.The different catalytic oxidation mechanisms between C3H6 and C3H8 combustion are revealed in depth.Construction of oxygen vacancy is of great significance for the development of high-efficiency VOCs catalytic oxidation catalysts.Due to the different molecular structures and different types of bonding in shortchain alkanes and alkenes,the different mechanism of action of surface oxygen vacancies in the catalytic oxidation of different molecules is still unclear.Herein,we synthesized oxygen-enriched Pt/TiO2-x catalysts by the NaBH4 liquid phase reduction method.Using propylene and propane as probe molecules,combined with experiments and theoretical calculations,we deeply revealed that oxygen vacancies have a strong effect on the catalytic oxidation of short-chain alkanes and slkenes.On the one hand,on the surface of the defective TiO2-x support,the oxygen vacancy localized electrons are transferred to the Pt nanoparticles,which promotes the formation of reducing Pt0 species,thereby improving the catalytic combustion efficiency of C3H6 through effective C=C double bond cleavage.On the other hand,the charge transfer between the interface between the Pt nanoparticles and the oxygen-rich vacancy TiO2 carrier promotes the formation of the chemically adsorbed peroxygen species O22-(Pt-O-O-Ti).The competitive adsorption of chemically adsorbed oxygen and C3H8 molecules severely inhibits the catalytic combustion of C3H8.This work provides insights for the rational design of efficient catalysts that activate C=C bonds in olefins or C-H bonds in alkanes.2.This work aims to tnvestigate the CuO/TiO2 interface structure,explore the relationship between highly stable Cu+species and the interface structure,and reveal the structure-activity relationship between the interface structure and the catalytic oxidation performance of CO.Copper-based catalysts have good application prospects in CO-related reactions,such as CO catalytic oxidation,water-gas conversion and other important industrial-related catalytic reactions.In the above reaction process,the interaction between Cu+sites and CO is a key reaction step to achieve effective catalysis.However,the instability of Cu+species(easy to be oxidized to Cu2+or reduced to Cu0)during the reaction limits the practical application of copper-based catalysts.We prepared a CuO/TiO2 catalyst with abundant and stable Cu+through the industrially mass-produced co-precipitation method,which significantly enhanced the CO lowtemperature oxidation activity.Combining experiments and theoretical calculations,it is evidenced that the Ti-doped CuO interface structure in the diffusion layer at the CuO/TiO2 interface is responsible for the excellent activity for the CO catalytic oxidation.The charge transfer in the interficial Ti-O-Cu hybrid structure promote the formation and stability of Cu+ species.CO molecules are adsorbed on the stable Cu+sites on the interface and directly react with them to generate CO2.This work proves that interface engineering promotes active lattice oxygen to increase the catalytic activity of CO oxidation at low temperature through the Mars-van Krevelen path.3.This work aims to explore the surface oxygen activation mechanism of the CuTiOx composite catalyst,reveal the structure-activity relationship between the nucleophilic surface lattice oxygen and the catalytic oxidation performance of C3H6.The reaction activity of the lattice oxygen on the catalyst surface has a directional guiding significance for the synthesis of high-activity and high-stability catalysts.Herein,we constructed abundant surface Cu induced active nucleophilic oxygen species on the surface of the CuTiOx composite nanocatalyst,which significantly improved the catalyst’s C3H6 low-temperature catalytic combustion efficiency(T90=212℃).Combining the structure characterization and density functional theory(DFT)calculations,it is firmed proved that the local electron cloud transfer in the Cu-O-Ti hybrid structure,which induced in the formation of the surface nucleophilic lattice oxygen.The generated surface nucleophilic lattice oxygen triggers the dissociation of methyl C-H,which promote the low-temperature catalytic C3H6 combustion.In-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)results show that the doped copper species is the main adsorption site for propene molecules.Combining the results of DRIFTS and DFT,it is confirmed that the nucleophilic surface lattice oxygen O2-on the catalyst surface can significantly promote the extraction of methyl C-H bonds in propene molecules and the subsequent complete oxidation to CO2.This work proves that surface doping induced nucleophilic oxygen is an effective strategy for rational design of next-generation environmental catalysts.4.The generation of active oxygen is an important part of heterogeneous catalytic oxidation.Highefficiency oxygen activation can improve the low-temperature oxidation activity of the catalyst,which is very important in air pollution control and other fields.We first predicted the stable structure of Cu1/TiO2 single-atom catalyst through DFT theoretical calculations,and preliminarily proved that Cu1/TiO2 single-atom catalyst is an effective strategy for constructing abundant active oxygen sites.Based on the DFT calculation results,we intelligently synthesized Cui/TiO2 single-atom catalyst,and further revealed the intrinsic mechanism of the dual activation of O2 molecules and surface lattice oxygen O2-.The charge transfer between the atomically dispersed copper atoms and the TiO2 support generates a large number of electron-rich Cu(I)species as chemical adsorption and activation sites for O2 molecules.Meanwhile,the Cu-O-Ti hybrid structure induces the distortion of the TiO2 lattice and effectively activates the adjacent surface lattice O2-species,achieveing the dual activation of O2 molecules and surface lattice oxygen.The activated surface lattice O2-directly reacts with CO molecules through the MvK mechanism.The dual-activated chemisorption O2 molecule can accelerate the replenishment of the consumed surface lattice oxygen O2-,and synergistically promote the catalytic performance.Our research results revealed that the dual activation of molecular oxygen and surface lattice O2-can be achieved by adjusting the electronic state of the metal species and optimizing the lattice structure of the reduced support in the single-atom catalyst,which significantly improves the heterogeneous catalytic oxidation activity. |
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