Reaction Mechanism Of Bimetal Oxide Oxygen Carriers For Chemical Looping Partial Oxidation Of Methane

Recently,as the breakthrough of shale gas mining technology,the extraction of nature gas mainly composed of methane has increased dramatically.The conversion of methane into valuable chemicals via syngas has attracted great attention.Compared with the traditional methane conversion methods,chemical looping partial oxidation of methane(CLPOM)has the advantages of low energy consumption,no air separation process and relatively high safety,attracting more attentions.Single metal oxides are usually unable to optimize the methane conversion and syngas selectivity simultaneously due to their drawbacks.Hence,the bimetal oxide as the active component has been under active investigation.The selection of oxygen carriers needs to consider two principles:(1)faster oxygen migration rate to oxidize the CH_x*in time,(2)the similar metal ions oxidation rate to avoid phase segregation.Therefore,a novel FeWO_x/Si O₂ is synthesized in CLPOM.The Fe-W alloy as active site can regulate the surface reaction kinetic.Besides,due to the modulation of Fe²⁺on the lattice oxygen of WO₃,more available oxygen with high activity can oxidize the CH_x*in time,improving the syngas yield.The stability of FeWO_x/Si O₂ during redox cycles is also explored.The strong interaction in Fe-W alloy formed in reduction process,and the similar oxidation rate between iron and tungsten cations during oxidation stage can suppress the phase segregation,improving the reaction stability.Besides,as the active component directly involved in CLPOM,the migration pathway and surface reaction mechanism of lattice oxygen are not clear,Ni O-CeO₂/Al₂O₃ was synthesized via two-step impregnation method to study the above problems.The superior performance is driven by the synergy between methane activation on Ni(O)site and highly active interface oxygen to oxidize the CH_x*in time reported by in situ characterizations.The study of surface reaction mechanism proposed more available Ce⁴⁺-OH with high activity can react with CH_x*species rapidly to suppress the carbon deposition and improve the catalytic performance.The migration pathway of three kinds of oxygen species and the corresponding oxidation products were explored.The Ce-O specie could provide lattice oxygen to the Ni-O-Ce specie continually to dominate in methane partial oxidation,improving the syngas selectivity.