Preparation Of Perovskite-type Electrocatalysts And Their Activation For Methane Conversion

Methane exists widely in nature in the form of natural gas and biogas,but the geographical dispersion makes the transportation of methane resources require a lot of capital investment.And the contribution of methane emissions to the greenhouse effect is much greater than that of CO2,so "methane conversion to methanol" has become a research hotspots of efficient utilization of methane resources.The industrially applied methane-tomethanol process is a two-step process,which requires first converting methane into syngas and then synthesizing methanol through catalytic reduction.The process is lengthy,high energy consumption,and expensive equipment costs.The direct conversion of methane to methanol under mild conditions faces the dual challenges of C-H bond activation and intermediate peroxidation.Therefore,researchers have proposed different research ideas such as homogeneous catalysis,heterogeneous catalysis,biocatalysis,photocatalysis,and electrocatalysis.Among them,electrochemical methods have received extensive attention for their ability to precisely control kinetics and product selectivity by controlling the potential.In order to further improve the conversion efficiency of electrochemical methane to methanol,the following research ideas in this paper are proposed: using ionic liquid([BMIM]BF4)containing trace water as the supporting electrolyte to control the active oxygen species generated in situ during the OER process on the anode surface,to interact with the methane molecules activated by the catalyst on the surface of the electrode,thereby improving the methanol generation rate and current efficiency.The main research portions and outcomes are as follows:(1)Three lanthanum-based perovskite compounds(La Fe O3,La Co O3,La Co0.5Fe0.5O3)are synthesized by hydrothermal method.SEM and TEM results show that La Co0.5Fe0.5O3 has the smallest average particle size.XRD and XPS characterization results confirm that the obtained compound has a perovskite crystal structure,and a considerable number of oxygen vacancies are introduced into the crystal lattice.The oxygen vacancy content is ranked as follows : La Co O3 > La Co0.5Fe0.5O3 > La Fe O3.(2)The as-prepared lanthanum-based perovskite compound is loaded on the electrode surface as the anode working electrode,and the electrochemical properties are studied in two supporting electrolyte systems(H2O + IL)and(H2O + IL + MeCN),prepared with trace water,aprotic ionic liquid([BMIM]BF4)and acetonitrile(MeCN)The results of electrochemical studies such as CV and LSV show that the electrode loaded with LCFO55 has the best catalytic water oxidation performance and methane response performance.The methanol generation rate and current efficiency are used as indicators to evaluate.The results show that the types of catalyst,anode potential and water content in the electrolyte have a significant impact on the methane conversion effect.The continuous electrolysis experiments are carried out in the(H2O + IL)electrolyte system.Under the optimized conditions,the LCFO55 electrode is electrolyzed for 1 h at a constant potential of 1.0 V in(H2O + IL)electrolyte system with a water content of 2 mol / L,and the methanol generation rate is 93.21 μmol gcat-1 h-1,the current efficiency is 65.78%.The viscosity of the electrolyte system(H2O + IL + MeCN)is significantly reduced after adding acetonitrile.The continuous electrolysis experiment is carried out in this electrolyte.Under the optimized conditions,the LCFO55 electrode is electrolyzed in the(H2O + IL + MeCN)electrolyte system with water content of 1 mol L-1 at constant potential of 1.0 V for 1 h,and the methanol generation rate reach 260.14 μmol gcat-1 h-1,the corresponding current efficiency is 35.9%.(3)Quantitative analysis methods for methanol in two systems(H2O + IL)and(H2O + IL + MeCN)are established based on headspace sampling-gas chromatography-mass spectrometry.The standard curves of methanol under different water contents of the two systems are established by external standard method and Mass Spectrometry SIM mode,and the linear correlation coefficients are all greater than 0.995.The test results of corresponding detection precision and spiked recovery show that they can content the needs of this research.