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.