Coprecipitated iron-containing catalysts(Fe-Al2O3,Fe-Co-Al_2O_3,Fe-Ni-Al_2O_3)for methane decomposition at moderate temperatures I.Genesis of calcined and reduced catalysts

摘要

Genesis of the composition and structure of the active component of coprecipitated iron containing catalysts(Fe-Al_2O_3,Fe-Co-Al_2O_3,Fe-Ni-Al_2O_3)with high metal loadings(>50 wt.%)for methane decomposition at moderate temperatures(600-650 C)has been investigated byxRD,EXAFS,radial electron density distribution(REDD),TEM,FTIR and Mossbauer spectroscopy.The main stages of the catalyst genesis during drying,thermal decomposition and reduction have been studied.For bimetallic systems(Fe-Co-Al_2O_3,Fe-Ni-Al_2O_3)intermediate spinel phases with a composition(M~II,Fe)3O4(M - Co,Ni)have been shown to form during heat treatment and reduction.This leads to a decrease of the reduction temperature for iron oxides.Reduced bimetallic catalysts(Fe-Co-Al_2O_3,Fe-Ni-Al_2O_3)are composed of alloys.The structure and parameters of their crystal lattices depend on the type and concentration of the added metal.Alumina has been shown to behave as a structural promoter.A model of the reduced catalysts consisting of highly dispersed(20-50 nm)metal and alumina particles with a spinel phase at their interface has been suggested.