Non-thermal Plasma Combining With Ti-based Perovskite Promoted Catalytic Oxidation For Atmospheric Hydrocarbon Pollutants

With global urbanization and industrialization,air pollution is one of the most severe challenges facing mankind.The vast majority of volatile organic compounds（VOCs）emitted into atmosphere threaten public health directly because of their carcinogenicity and teratogenicity,and also emerge as a serious environmental hazard as they are the major precursors of photochemical smog and haze.In addition,improper emission of methane as a greenhouse gas or a large amount of carbon dioxide released from direct combustion of methane,which will aggravate global warming.More and more attention has been paid to the reduction and utilization of greenhouse gases.Due to the inactivity of most atmospheric hydrocarbon pollutants,especially methane,the traditional catalytic oxidation processes usually involve high temperature or need to be combined with high pressure and other conditions,and the harsh reaction conditions put forward higher requirements for industrial equipment and application place.Coupling of nonthermal plasma with catalyst has attracted extensive attention due to its simple device and its ability to transform atmospheric hydrocarbon pollutants at room/near-room temperatures and atmospheric pressures,and is considered as a promising alternative method to tackle those challenges.Synergy between plasma and catalyst has demonstrated its benefits or shows future potential,but the efforts to improve the synergy remain both highly desirable and challenging.The plasma-catalytic performances for atmospheric hydrocarbon pollutant conversion over Ti-based perovskite and the plasma-catalytic synergy mechanism were studied.The main conclusions are as follows:（1）A series of nano Ba_1-xCe_xTi O₃ perovskite catalysts with excellent specific surface areas and oxygen storage capacity are prepared by a simple two-step method,and the plasma-catalytic performances of toluene over the catalysts are investigated.The XPS,EPR,Raman,H₂-TPR,and OSC results suggest that the doped Ce cations occupy the A-sites of BaTiO₃ and promote the formation of the oxygen vacancies（V_O）and Ti³⁺.Superoxides（^·O₂^-）are identified as the primary reactive oxygen species and are reversibly generated on the surface.Reactive oxygen species enriched on the catalyst surface can significantly enhance the deep plasma-catalytic degradation of toluene,thus obtaining excellent catalytic activity and stability.（2）Different N-doped perovskite catalysts with excellent specific surface areas are prepared through different N-doped strategies to investigate the plasma-catalytic decomposition of toluene and ethyl acetate.The aberration-corrected STEM,XPS,EPR,EXAFS,OSC,and DFT results demonstrate that the partial substitution of oxygen by nitrogen triggers the electronic reconstruction and local disorder,thus modulating the electronic properties and coordination structures contributed to the formation of V_O-Ti³⁺pairs.The perovskite catalysts combined with plasma show a significant synergistic effect,which achieves 100%toluene conversion and 81%carbon dioxide selectivity under ambient conditions.The energy efficiency of toluene decomposition and carbon dioxide generation is obviously competitive.The plasma-catalytic performances of VOCs are dominated by the catalytic properties of catalysts rather than the dielectric properties.The catalytic properties of the investigated catalysts have some universality to different VOCs decomposition.（3）The plasma-catalytic toluene decomposition on the catalyst surface is dynamically observed by designing various in-situ characterization devices and methods under continuous plasma conditions,including quasi in-situ EPR,in-situ Raman and operando DRIFTS.The V_O-Ti³⁺pairs are identified as active sites for the plasma-catalytic decomposition of toluene,instead of isolated V_O.The V_O-Ti³⁺pairs with favorable electron transfer characteristics energetically prefer to capture and utilize vibrationally excited oxygen species at the plasma-catalyst interface.The introduction of the local defects into the catalyst structure facilitates the activation of lattice oxygen by plasma to participate in surface reactions at near room temperature.Anhydride decomposition is considered to be a rate-limiting step of surface toluene decomposition,and the plasma-catalytic interfacial synergy can significantly improve the generation of by-products,especially the anhydride decomposition.（4）Nanorod-like BaTiO₃ and Ni/BaTiO₃ catalysts are prepared.Aqueous electrode as the ground electrode of a plasma DBD reactor is designed and used,which realizes the plasma-catalytic partial oxidation of methane to liquid oxygen-containing compounds at ambient temperature and pressure.Increasing oxygen content in reaction gas can enhance methane conversion,which reduces the selectivity of oxygen-containing compounds to a some extent.At the input power of 11 W,the nanorrod-like BaTiO₃ achieve the highest liquid product selectivity of 70.1%,and the nanorrod-like Ni/BaTiO₃ obtain the highest 34.5%formaldehyde selectivity and 27.3%methanol selectivity（total selectivity of 61.8%）.The total selectivity of formaldehyde and methanol obtained by nanorrod-like Ni/BaTiO₃ at 11 W is 97.8%in the liquid product,and the catalysts present excellent stability in the 30-hour test.In this study,the efficient plasma-catalytic oxidation of atmospheric hydrocarbon pollutants is realized.Through the design of various operando/in-situ characterization devices and methods,the mechanism of plasma-catalytic interfacial synergy promoted by active sites is revealed,which provides theoretical support for the further design of heterogeneous catalysts and has certain practical significance for the development and application of plasma-catalytic system.