Perovskite catalysts for the catalytic flameless combustion of methane

Abstract

A new method was employed for the preparation of a set of lanthanum cobaltites of general formula La1-xMxCoO3+ with M=Ce, Eu and x=0, 0.05, 0.1, 0.2. All the samples so prepared showed 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 of methane was by ca. one order of magnitude higher than that of their analogues, prepared through the usual calcination-milling 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 vs. x values could be set up: 0.1 Ce > 0.05 Ce > 0 > 0.05 Eu > 0.1 Eu  0.2 Ce. 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 sulphur poisoning on perovskite catalysts prepared by flame-pyrolysis

“…Catalytic activity data for methane combustion are reported in Table 2 and in Fig.3. At difference with what reported elsewhere [8], doping at A position did not bring about very significant effects on catalytic activity, i.e. T50 were similar for differently substituted samples, at least within the detection limits of the detection apparatus (vide supra).…”

“…La-based catalysts with ABO3 perovskite-like structure [1][2][3][4] have been proposed as a valid alternative for the present application. Indeed, perovskite catalysts combine low cost, thermo-chemical stability at high operating temperature and satisfactory catalytic activity [5][6][7][8]. In spite of this, there are still some open questions, especially regarding their resistance to sulphur poisoning when used for the CFC of methane.…”

Preparation of LaFe0.95Pd0.05O3 perovskites and their catalytic performances in methane combustion

“…At higher temperatures, however, CH 4 combustion occurred as an intrafacial process, which involved the bulk oxygen species and was usually preferred at temperatures higher than 673 K [26,27]. The lattice oxygen species migrated from the bulk toward the surface and participated in methane oxidation.…”

Catalytic combustion of hydrocarbons over perovskites

“…Both A and B can be partially substituted, leading to a wide variety of mixed oxides of general formula A1-xA'xB1-yB'yO3, characterised by structural and electronic defects, owing to their non-stoichiometry, indicated by the  subscript in the formula. For full oxidation reactions, such as CFC, the cation B is considered the responsible of catalytic activity [1], while the cation A, especially when partially substituted with a cation A' of different valence, governs the formation of crystal lattice vacancies and can stabilise unusual oxidation states for B, leading to different catalytic performance [1][2][3]. The oxidation activity of perovskites has been ascribed to their ionic conductivity, to oxygen mobility within their lattice [2], to their reducibility and to their oxygen sorption properties [4].…”

“…In it bulk oxygen migrates towards the surface, becoming available for the oxidation of the adsorbed substrate and it is quickly replaced by oxygen coming from the gaseous phase. The mobility of O 2-ions in the crystalline framework determines the mechanism of the catalytic reaction [3].…”