resumo
Mixed-conducting SrFe0.7Al0.3O3-delta (SFA) exhibits substantial catalytic activity towards partial oxidation of methane and can thus be considered as a component of monolithic ceramic reactors for synthesis gas generation, where the dense membrane and porous catalyst at the permeate-side surface are made of similar compositions. Surface modification of SFA powder and membranes with Pt has no essential effect on the performance of a model reactor, suggesting that the catalytic behavior of SFA is mainly determined by the surface states of iron and oxygen ions in the catalyst. The Mossbauer spectroscopy shows that reduction of SrFe0.7Al0.3O3-delta, having cubic perovskite lattice in air, leads to the co-existence of perovskite- and brownmillerite-like domains, whilst the concentrations of metallic Fe and even Fe2+ under typical operation conditions are lower than the detection limits. The amount of vacancy-ordered phase increases with decreasing oxygen content, the estimations of which were confirmed by coulometric titration data. The catalytic activity of ferrite-based materials may thus be associated with lattice instability characteristic of morphotropic phase transformations.
palavras-chave
METHANE OXIDATION; OXYGEN; SURFACE; GAS; TECHNOLOGIES; CONVERSION; STABILITY; VACANCIES
categoria
Chemistry
autores
Kharton, VV; Waerenborgh, JC; Rojas, DP; Yaremchenko, AA; Valente, AA; Shaula, AL; Patrakeev, MV; Marques, FMB; Rocha, J
nossos autores
Aleksey Yaremchenko
Investigador Principal
Anabela Tavares Aguiar Valente
Investigador Principal
Fernando Manuel Bico Marques
Professor Catedrático
João Rocha
Prof. Catedrático