L. Fabbrini

Perovskite catalysts for the catalytic flameless combustion of methane: Preparation by flame-hydrolysis and characterisation by TPD–TPR-MS and EPR

Abstract A new method was employed for the preparation of a set of lanthanum cobaltites of general formula La1−xMxCoO3+δ with M=Ce, Eu and x=0, 0.05, 0.1, 0.2. All the samples thus prepared were nanostructured, thermally very stable and characterised by highly crystalline perovskite-like structure and high surface area. Their activity as catalysts for the catalytic flameless combustion (CFC) of methane was by ca. one order of magnitude higher than that of their analogues, prepared through the usual calcination-milling (CM) procedure. Adsorption of oxygen was accompanied by formation of paramagnetic species. Desorption of preadsorbed oxygen was dependent on the nature of the doping element and on the value of the stoichiometric coefficient x of their formula. A correlation between the temperature of the maximal rate of oxygen release and catalytic activity was found. The following scale of activity for the title reaction versus x values could be set up: 0.1Ce>0.05Ce>0>0.05Eu>0.1 Eu≅0.2Ce. The higher activity of Ce-doped catalysts as compared to those doped with Eu was found to be related to the strength of the bond between oxygen and Co ions.

Effect of primer on honeycomb-supported La0.9Ce0.1CoO3±δ perovskite for methane catalytic flameless combustion

Abstract A set of La0.9Ce0.1CoO3 combustion catalysts, supported onto commercial cordierite monoliths, through either La2O3 or Al2O3 as primer, was prepared with different active phase/primer combinations. Two different salts were tested as precursors of the La-based primer. The behaviour of the catalysts for the methane flameless combustion was compared with that of samples prepared in the absence of any primer. The primers and the active phase were deposited by means of the dip-coating technique. The preparation conditions of the suspension and/or solution for the dip coating were studied, aiming at obtaining a uniform and resistant deposition. The catalysts were characterised, before and after the activity tests, by BET, X-ray diffraction analysis (XRD) and scanning electron microscope (SEM). The comparison between the catalysts showed that with Al2O3 as primer the catalyst possesses a higher surface area (SA) and hence a higher initial activity, while with La2O3 as primer a very high thermal stability can be obtained.