Search

A set of La1− x A′ x Co1− y Fe y O3±δ 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), N2 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. [ABSTRACT FROM AUTHOR]

Abstract: The activity of honeycomb supported LaBO3±δ (B=Fe, Mn and Co) and La2NiO4 was tested for the catalytic flameless combustion (CFC) of methane and compared with their catalytic behaviour in powder form. Catalyst supporting brought about some modifications, mainly the complete loss of the suprafacial activity. Furthermore, thermal resistance of supported samples was checked through accelerated deactivation tests and showed to strongly depend on the nature of the B ion. Structural and morphological properties of fresh and aged catalysts, both in powder form (either pure or mixed with the primer precursor) and as honeycomb-supported samples, were compared to investigate the effect of each step of the dip-coating procedure. This allowed to shed light on the causes of the structural and chemical changes occurring during the wash-coating and leading to more or less severe decrease of performance and of thermal resistance of the final catalyst. [Copyright &y& Elsevier]

Abstract: Several samples of Sr1–x Ag x TiO3±δ (, 0.1) perovskite-structured catalysts were prepared and tested for the title reaction under lean-burn conditions. For the same overall nominal composition, catalyst activity and durability depend strongly on the method of preparation and, for the samples prepared by the same method, mainly on temperature and on the residence time at such a temperature during preparation. In Sr0.9Ag0.1TiO3±δ catalysts Ag is present either as intra-crystalline Ag2+, likely substituting for Sr2+ in the perovskite lattice, or as inter-crystalline metallic Ag. The catalytic activity of Sr0.9Ag0.1TiO3±δ is connected with the presence of , , and ; of , O−/Sr2+; or of O−/Ti4+ species, depending on preparation method and conditions. Furthermore, inter-crystalline metallic Ag plays an important role in improving catalyst resistance to sintering; the most durable samples are those calcined for a sufficient residence time at the highest temperature during preparation, that is, under conditions more favourable to the segregation of this metal from the perovskite lattice. [Copyright &y& Elsevier]

Abstract: To understand better the effect of La2O3 as primer for the preparation of honeycomb supported La0.9Ce0.1CoO3±δ catalyst, some samples were prepared starting from different La-precursors. Physical and morphological properties of both the primer-coated honeycomb and its precursors (as-prepared and after thermal treatment at different temperature) have been investigated by TGA, TPD–MS, XRD and SEM. Calcination at high temperature brought about a rearrangement of both primer and active phase morphology. When La acetate was used as precursor, such a transformation seemed not to alter substantially the morphology of the primer layer, leading to a poorer anchoring to the support, with deep cracking and exfoliation of the La oxide platelets so formed. By contrast, when the primer precursor was La nitrate, the higher reactivity of the hydroxynitrates, forming during calcination, with respect to both the active phase and the honeycomb, led to a more uniform and compact La2O3 layer, anchoring much better the perovskite to the monolith support. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]