Synthesis Of Mn Based Perovskite Composite Metal Oxides And Their Catalytic Pyrolysis Performance Of Lignin

A series of lanthanum doped calcium manganate oxides(Ca_1-xLa_xMnO₃,CLM-x)were synthesized by sol-gel method,and the synthesis conditions were optimized.The crystal phase,microstructure,pore structure and thermal stability of the synthesized perovskite samples were characterized by means of X ray diffraction（XRD）,scanning electron microscope（SEM）,specific surface area analyzer（BET）and thermogravimetric differential thermal analysis（TG）.By adding surfactants and nano-metal oxide MnO₂ with metal active centers and a large number of oxygen vacancies,a composite metal oxide MnO₂/CLM-0.5 with higher specific surface area and catalytic activity with perovskite as the carrier was synthesized.The synthesized catalyst was used to carry out the catalytic pyrolysis experiment of lignin,and the composition of the liquid phase product was characterized and analyzed by gas chromatography-mass spectrometry（GC-MS）.Finally,the oxidation regeneration experiment of the reacted catalyst was carried out to investigate catalyst regeneration performance.The conclusions are as follows:（1）The optimal synthesis conditions of CLM-0.5 were as follows:x=0.5,oil bath temperature T=80°C,precursor pH=8,air atmosphere calcination,calcination temperature is800°C.CLM-0.5 was cubic crystal phase and porous structure,the specific surface area is22.65m²/g.（2）The synthesis of CLM-0.5 was regulated by template agent Cetyl trimethyl ammonium bromide（CTAB）and SiO₂ as templates.The study found that the specific surface area of the synthesized CLM-0.5 increased by 4.18m²/g and 1.67m²/g,respectively.MnO₂/CLM-0.5composite metal oxide was successfully synthesized by adding metal oxide MnO₂.（3）The thermogravimetric analysis results of the catalytic pyrolysis of lignin showed that both CLM-0.5 and MnO₂/CLM-0.5 had obvious catalytic effects on lignin,and the temperature at the end of pyrolysis was reduced by 42°C and 60°C,respectively,indicating that the two catalysts could significantly reduce the activation energy of lignin pyrolysis.（4）The results showed that the optimal pyrolysis conditions were as follows:m（BL）:m（CAT）=3:1,and the pyrolysis temperature was 650℃.When CLM-0.5 was used as catalyst for lignin pyrolysis,the yield of gaseous products decreased by 7.44%,and the yield of liquid products increased by 12.53%.The main products were phenol,guaiacol and eugenol,and the total selectivity reached 63.5%.It indicated that CLM-0.5 could inhibit decarboxylation and decarbonylation during lignin pyrolysis,and promote the cleavage of alkyl side chain on benzene ring.When MnO₂/clm-0.5 was used as catalyst for lignin pyrolysis,the yield of liquid products increased by 13.96%,and the selectivity of Syringol reached 30.23%,which indicated that MnO₂/CLM-0.5 had higher catalytic activity for lignin pyrolysis.（5）The crystal phases of CLM-0.5 and MnO₂/CLM-0.5 after regenerating for 5 times remain basically unchanged,and their morphologies change slightly,the yields of the liquid-phase products of CLM-0.5 and MnO₂/CLM-0.5,which were regenerated by oxidation for 5times,did not change obviously after the reaction with lignin.The results showed that CLM-0.5 and MnO₂/CLM-0.5 still had good activity and stability after repeated pyrolysis-regeneration.