Methane Selective Oxidation Via Photocatalysis And Nonthermal Plasma Catalysis

Effective activation of the methane C-H bond and the conversion of methane as the feedstocks for the production of high value-added chemicals under mild conditions is of great significance.The methane molecules are very stable,and it is difficult to selective oxidize methane at room temperature and pressure.Photocatalysis and nonthermal plasma are effective methods for selective oxidation of methane at room temperature and pressure.However,in previous reports,there are still problems such as low methane conversion rate and low product selectivity.In this paper,Fe-N-C catalysts,metal-organic frameworks（MOFs）-based catalysts,and polymer carbon nitride（PCN）-based catalysts were prepared for selective oxidation of methane at room temperature and pressure by means of photocatalysis and plasma catalysis.The main research contents are as follows.（1）Fenton-type Fe-based catalysts containing Fe-N_x sites and Fe/Fe₃C nanoparticles were prepared and used as a model to study the decomposition mechanism of H₂O₂ by different iron species.Fe-N_x in the low spin state provides the active site for hydroxyl radicals（·OH）generation.Fe/Fe₃C,in particular Fe₃C,promotes Fe-N_x sites for the homolytic cleavages of H₂O₂ into·OH,but Fe/Fe₃C nanoparticles（Fe⁰ as the main component）with more electrons are prone to the undesired O₂ generation.Hydroxyl radicals have strong dehydrogenation ability and can activate methane C-H bonds.With a catalyst benefiting from finely tuned active sites,18%conversion rate for the selective oxidation of methane was achieved with about 96%selectivity for liquid oxygenates（formic acid selectivity over 90%）.Importantly,O₂ generation was suppressed 68%.This work provides guidance for the efficient utilization of H₂O₂ in the chemical industry.（2）Ui O-66-NH₂ with high specific surface area was used as the support,and the highly dispersed Fe O_x species were introduced through a simple dip-calcination method.The catalyst was introduced into the plasma catalytic system and the experimental conditions were optimized.The methane conversion rate in the flow reactor can reach 33.3%,the liquid oxygenates selectivity can reach 53.9%（methanol selectivity:45.3%）.Power consumption is only 7.5 W.The reactive species and the reaction paths in the reaction were analyzed in detail,and the reaction mechanism suitable for this reaction was proposed.（3）The polymer carbon nitride was used as the support,and the cuprous oxide nanoparticles were introduced through the dip-calcination method to etch the bulk carbon nitride to increase the specific surface area and increase the active sites.The catalyst was introduced into the nonthermal plasma catalytic system.The methane conversion rate in the flow reactor is 27.6%,and the liquid oxygenates selectivity is as high as 63.4%.The reaction also realized C-C coupling.Ethanol and acetone are the main C₂+oxygenates（selectivity:20.7%）.A reasonable speculation was made on the mechanism of the catalyst’s promotion of C-C coupling,and the role of photocatalysis in the reaction was explained.