Study On Compositional Type La-Hexaaluminate Methane High-Temperature Combustion Catalysts

A series of LaMAlO_19-δ-5(M=Fe, Co, Mn, Ce)hexaaluminates were prepared by conventional co-precipitation method, as well as compositional catalysts combined Mn and Ce species with La-Hexaaluminate by impregnate and impregnate-precipitation methods. The samples were characterized by XRD, BET, TPR, FT-IR, XPS, TEM and tested methane combustion activity at the same time.The results showed that series of transitional metals(Fe , Co, Mn) substituted La-hexaaluminates could improve the catalysts activity of methane combustion. However, the effect promoting catalytic performance can not assimilate to that of CeO2-combined La-Fe-hexaaluminate.The catalytic activity of LaCe_0.8Fe_0.2Al₁₁O_19-δ was the best for methane oxidation with T_10% at 475℃ by co-precipitation.The result of XRD showed that Ce species could not substitute Al in La-Fe-Hexaaluninate, but formed La-absence hexaaluminate; XPS and electrical conductivity test revealed that Ce species could insert La-absence site in hexaaluminates lattice. The coordination effect of Ce and Fe impaired Fe=O bond, therefore this is the reason for high activity of LaCe_0.8Fe_0.2Al₁₁O_19-δ. In addition, Mn-LaFeAl₁₁O₁₉ prepared by impregnate-precipitation method (calcined at 800℃) had excellent catalytic activity among La-hexaaluminates combined manganic species,however ,was not stable under high temperature.After calcined 1400℃ for 3h, combined Mn species with LaFeAl₁₁O_19-δ gave birth to phase-conversion, leading to catalytical activity decrease.