Effect of preparation method on activity and stability of LaMnO3 and LaCoO3 catalysts for the flameless combustion of methane

A set of LaMnO3 and LaCoO3 catalysts was prepared through different synthesis procedures. The selected techniques included the sol-gel method, flame hydrolysis from aqueous solution, complexation through EDTA and solid-state reaction. The last was accomplished through reactive grinding by ball-milling either in a vibration mill or in a planetary mill. EDTA complexation was applied for LaCoO3 only and did not improve significantly catalyst activity or stability, with respect to other techniques. Ball-milling never allowed obtaining a pure perovskitic phase, at least under the most energetic grinding conditions permitted by our apparatus. The highest activity for the catalytic flameless combustion of methane was obtained with the sol-gel prepared samples, though thermal resistance revealed insufficient for high temperature applications. A bit lower activity, but coupled with good thermal stability was obtained with the samples prepared through flame hydrolysis

La1-x A ' xCo1-yFe (y) O-3 +/-delta (A ' = Ce,Sr) catalysts for the flameless combustion of methane

A set of La1-x A' (x) Co1-y Fe (y) O-3 +/-delta samples (A'= Ce,Sr; x= 0.1, 0.4, y= 0, 0.5, 0.8, 1) was prepared by means of the sol-gel citrate method and characterised through X-ray diffraction (XRD), N-2 adsorption/desorption and temperature programmed desorption-reduction (TPD-TPR). Their activity for the catalytic flameless combustion of methane was tested and the results interpreted focusing on the effect of doping at A and/or B position. It was found that Ce doping of lanthanum ferrite catalysts could suppress suprafacial activity and slightly enhance intrafacial activity, due to the change of oxygen mobility. However, catalytic activity seems independent of the type of electronic conductivity (p- or n-type), the activity of an analogously Sr-doped sample being similar to that of the Ce-doped one. Mixed B-metal composition can help in modulating both oxygen mobility and catalyst stability under reducing reaction conditions. High Fe content allows to optimise this last parameter. However, depression of oxygen mobility and hence of activity has to be prevented by proper doping at A-position