Conversion Of Methane With TiO₂ Based Photocatalyst And Its Mechanism

People paid attention to the energy crisis and climate issues because of the increasing crude oil consumption and greenhouse gas emissions.Methane（CH₄）has attracted extensive attention for its abundant reserves.Different from the thermal energy of industrial route,photocatalysis has emerged as the green and clean pathway to activated CH₄ under mild conditions through the injection of photo-induced charge carrier.The strategies of surface modification and constructing heterojunctions were used to modify TiO₂,which is cheap,available and nontoxic but has a wide bandgap.In this paper,the modified TiO₂ could be used for efficient photocatalytic CH₄ conversion and the mechanism of photocatalytic CH₄ conversion was revealed.The specific research contents are as follows:Firstly,introducing defects on the surface of commercial TiO₂,and then photo-depositing Pd nanoparticle as cocatalyst.The CH₄ conversion performance shows that the highest yield of C1products reached 54693μmol·g^-1·h^-1 over the optimal photocatalyst Pd_0.5-def-TiO₂,almost 14and 4 times that of pristine TiO₂ and def-TiO₂.The characterization results show that Pd and OVs act as the hole and electron acceptors,respectively,which promoted carrier separation.Secondly,the heterojunction was constructed by compounding g-C₃N₄ with C-TiO₂,which promotes the separation of photogenerated carriers in the composite and increases the utilization of carriers.The yield of formaldehyde（HCHO）over the photocatalyst C-TiO₂/g-CN-5 can reach 25.37μmol after 2 h illumination,almost 7.5 times and 1.6 times that of pristine g-C₃N₄and pure C-TiO₂,and the selectivity of HCHO can reach 98.2%.In this paper,the modified TiO₂ for CH₄ conversion exhibites the better performance and optimizing selectivity.Introducing surface defects and noble metals could promote the CH₄conversion performance.In addition,the method of constructing heterojunction with g-C₃N₄elevates the selectivity of products.These two ways enrich the modification strategy of TiO₂for CH₄ conversion and the mechanism of the reaction process.