Design Of Cocatalyst In Photocatalytic Methane Conversion

Methane is not only an important fossil energy source,but also a major greenhouse gas.Therefore,converting methane into value-added chemicals has important implications.However,owing to the extremely stable molecular structure of methane,the conversion of methane is usually carried out under high temperature and high pressure.Such reaction process requires high energy consumption,and releases enormous carbon dioxide into the atmosphere.Photocatalysis provides a feasible way to address the above issue,which utilizes solar energy rather than heat to activate the first C-H bond in methane and subsequently converts methane into value-added chemicals.However,there are still great challenges in increasing methane conversion rate,improving the selectivity of products,and reducing catalyst cost.In this paper,in order to regulate the photogenerated carrier kinetics and adsorption of reaction substrate,the role of cocatalysts in photocatalytic methane conversion was systematically studied.The results show that the well-designed cocatalyst can not only accelerate the migration of photogenerated charge carriers,but also promote the adsorption and activation of O₂/H₂O towards enhanced production of reactive oxygen species（ROS）.By virtue of the above merits,high activity and selectivity in the conversion of methane to value-added products was achieved.The main research contents are as follows:1.TiO₂ nanosheets with surface phosphates and oxygen vacancies were prepared for photocatalytic methane conversion.Phosphates and oxygen vacancies can not only promote the separation of photogenerated charge carriers,but also accelerate the transfer of photogenerated cahrge carriers from catalyst to substrate.Moreover,the phosphates and oxygen vacancies can serve as effective sites for the activation of H₂O and O₂,respectively,and thus boost the yields of ROS.Benefitted from the synergy of surface phosphates and oxygen vacancies,a high selectivity for liquid products up to94.2%was achieved in photocatalytic methane conversion,with the apparent quantum efficiency reaching 19.8%.This work provides a new angle for improving the photocatalytic methane conversion activity under aerobic conditions.2.Fe³⁺sites were successfully anchored on TiO₂ nanosheets for efficient photocatalytic methane conversion.First,Fe（OH）_x species are loaded onto TiO₂nanosheets by chemisorption deposition method.After acid leaching,Fe（OH）_x species are converted into coordinatively unsaturated Fe³⁺sites.Mechanism studies show that the Fe³⁺site can not only accelerate the separation of photogenerated electrons and holes,but also promote the adsorption and activation of oxygen,thus enhancing the yield of·OH for efficient conversion of methane to formaldehyde at room temperature.This work provides a new way for designing high-performance,low-cost photocatalytic methance conversion systems.