Application And Investigation Of La₂O₂CO₃ Catalysts For Oxidative Coupling Of Methane

Oxidative coupling of methane(OCM)is an important way to convert methane directly to C2(ethylene and ethane).It is a vital research direction of OCM catalyst to reduce the activation temperature of methane and inhibit the formation of by-products.Due to the existence of CO32-,La2O2CO3(LOC)catalyst has a certain inhibition effect on CO2,which is a kind of deep oxidation product.However,the application of LOC catalyst in OCM reaction is relatively few.Therefore,the structure-activity relationship of the catalyst is studied from the perspective of preparation method and ion doping of the catalyst.On this basis,the LOC catalysts and the doped LOC catalysts are developed.The catalysts have good OCM catalytic performance.The main results are as follows:1.LOC-T,LOC-N,LOC-M and LOC-P catalysts with different morphologies(tremella,rod,granular and flake)were synthesized by template hydrothermal method(T),normal hydrothermal method(N),microemulsion method(M)and precipitation method(P)respectively.The results show that the catalytic performance of the LOC catalyst obtained by different preparation methods is related to its different morphology.The tremella-like LOC-T catalyst synthesized by template hydrothermal method has hierarchical pores,the existence of surface defects enriches the active oxygen species,enhances the activation capacity of oxygen,reduces the ignition temperature of OCM reaction,which is conducive to reduce the ignition temperature of OCM reaction.Meanwhile,the tremella-like LOC-T catalyst contains more moderate alkaline sites,which is beneficial to C2 product desorption.Therefore,the C2 yield of the LOC-T catalyst can be 18.2%at 460℃ temperature.2.the stability of the LOC-T catalyst was studied.At 460℃,the conversion of methane,the selectivity and yield of C2 remained unchanged after 35 hours of reaction on the LOC-T catalyst.Before and after the reaction,the morphology of the hierarchical pores of the LOC-T catalyst did not change significantly,and the existence of water vapor during the reaction did not collapse the hierarchical pores.When the temperature of water vapor is lower than 550℃,the hierarchical pores of the LOC-T catalyst will not be destroyed.Therefore,the catalyst of LOC-T has good stability.3.the LOC-T catalysts doped with different valence ions(Sr2+,Y3+,Zr4+)were prepared,and the structure-activity relationship of the catalysts was also investigated.The results show that with the increase of the valence state of doped ions,the hierarchical pores of tremella-like LOC-T catalyst is gradually changed,the oxygen vacancy concentration decreases,the adsorption activation oxygen capacity decreases,the moderate alkaline sites decrease,and the ignition temperature and C2 selectivity of OCM reaction decrease.Therefore,the Sr-LOC-T catalyst has the best OCM performance.At 420℃,the C2 selectivity and yield of Sr-LOC-T catalyst are 58.8%and 20.2%respectively.