A Novel Photocatalytic Material For Methane Conversion

Since the Industrial Revolution,human development has led to an increasing consumption of fossil fuels such as petroleum and coal.However,the excessive use of fossil fuels has caused global pollution and exacerbated climate change.As a recognized clean energy source,natural gas has advantages of abundant reserves and low prices.Moreover,the combustion products of its main component,methane,are only water and carbon dioxide,which has drawn increasing attention to methane utilization.In order to achieve the goal of carbon neutrality,this paper focuses on the utilization and conversion of methane and investigates methods for solar-driven methane steam reforming into synthesis gas and methane steam coupling to ethane.Given the significant geometric and polarity differences between methane and water,simultaneously activating both reactants is a key challenge in the entire reaction.This paper explores X/GaN@InGaN NWs（X represents co-catalysts）semiconductor composite materials,aiming to address this crucial issue through innovative catalytic materials.By utilizing photocatalytic reactions,the efficient reaction between methane and water is achieved,and the selectivity of the reaction products is controlled by manipulating the co-catalyst type,leading to different product routes.This paper proposes a green and efficient strategy by harnessing abundant solar energy for the reaction between methane and water.The main research contents of this paper are as follows.1.RhO_x/GaN@InGaN NWs/Si Photocatalytic Methane Steam ReformingA new type of semiconductor hybrid material was developed by decorating vertically aligned GaN/InGaN nanowires with ultrafine RhO_xnanoclusters.Through relevant theoretical calculations,microscopic characterization,and in-situ spectroscopic measurements,it was found that the combination of RhO_x/GaN@InGaN nanowires possesses unique properties,enabling the simultaneous activation of CH₄ and H₂O,thanks to the Lewis acid/base nature of the RhO_x/GaN interface.With the assistance of photo-generated high-energy charge carriers,non-polar CH₄ can easily be decomposed into CH₃ and H species,while H and OH are more favorable for decomposition from water.Subsequently,the CH₃ and OH species tend to reside on the Rh sites,while H prefers to be adsorbed on the N sites of GaN.The adsorbed active species CH₃,OH,and H then evolve into synthetic gas through energetically favorable pathways,thus overcoming the thermodynamic limitations of producing synthetic gas from CH₄and H₂O under near-ambient conditions.Excellent synthetic gas activity was achieved under concentrated light irradiation of 6.3 W·cm^-2 without the need for additional energy input,reaching 8.11 mol·g_cat^-1·h^-1.The H₂/CO ratio can be flexibly adjusted from 2.4 to 0.8,and during 3 hours of operation,the conversion of each mole of Rh reached up to 10,493 mol CO+H₂.This study demonstrates a green pathway for solar-driven methane steam reforming to produce synthetic gas.2.Au NPs/GaN NWs/Si Photocatalytic Methane Steam CouplingBy designing a rational composite material consisting of Au NPs/GaN nanowires/Si,and utilizing it as an efficient photocatalyst,researchers have achieved selective coupling of CH₄ to C₂H₆with high productivity(20 mmol·g^-1·h^-1),high selectivity（66%）,and exceptional durability in a quartz-sealed reactor.Through theoretical calculations,electron microscopy characterization,and in situ spectroscopic measurements,it was discovered that the multifunctional interface of Au NPs/GaN,compared to RhO_x/GaN,effectively activates both CH₄ and H₂O by stretching the C-H and O-H bonds.Additionally,it lowers the required Gibbs free energy in the crucial step of methyl formation.As a result,gold nanoparticles are more conducive to methane coupling and enable easier preservation of the coupled products compared to rhodium.These findings provide a green pathway for the solar-driven coupling of methane steam to produce ethane.