Semiconductor Based Photocatalytic Materials For Methane Activation At Low Temperature

Effective activation of the methane C-H bond and conversion of methane（natural gas）to a mixture of more valuable hydrocarbon derivatives under mild conditions is always one of the key scientific challenges in the fields of catalysis and chemistry.Photocatalysis arises as a promising green strategy which could exploit hydroxyl radical（·OH）to accomplish methane activation.The cleavage of the methane C-H bond at the center is achieved by constructing FeNx center.A precursor is prepared by using a ferrous salt as a metal source as a ligand.The high nitrogen content of the melamine incorporation precursor was used for calcination to obtain more dispersed FeNx centers,and the effects of temperature and doping ratio on photochemical and photophysics properties were examined.Studies have shown that FeNx center production is the key to methane adsorption activation.Through a series of characterization methods,it is proved that the adsorption and activation of methane molecules in the FeNx center produces methyl radicals.On the other hand,the added hydrogen peroxide forms a light-like Fenton cycle with Fe（Ⅱ）and Fe（Ⅲ）.The decomposition of hydrogen peroxide produces hydroxyl radicals,which are capable of oxidizing free radicals to produce a series of organic derivatives such as methanol and ethanol.We use a wide range of graphite phase carbon nitride and ammonium tungstate as raw materials to prepare tungsten oxide-nitrogen by simple one-step pyrolysis.The catalytic materials have a heterojunction structure of carbon.Through fluorescence tests,it is found that the composite material has a good separation of photogenerated electrons and holes,and a large amount of holes and water act to generate hydroxyl radicals,so the photocatalytic oxidation ability is far superior to that of the single constituent material.It can also show excellent performance and good cycle stability in methane activation oxidation.The use of terephthalic acid,metal salt and triethylamine as raw materials to prepare a metal organic framework structure as a precursor,one-step pyrolysis can produce a nickel oxide structure with graphene is used for electron transport,and the material with oxygen vacancies as the active center.The internal electron hole separation and transfer path is constructed by nickel oxide,which exhibits high methane conversion activity.By comparing commercial nickel oxide and Ni/Ce O₂ materials,it is found that they have huge advantages in terms of raw material economic and methane selectivity.The yield of the product ethanol for 4 h reaction can reach 777.9 umol/g_cat.