abstract
The steady-state CH4 conversion by oxygen permeating through mixed-conducting (SrFe)(0.7)(SrAl2)(0.3)O-z composite membranes, comprising strontium-deficient SrFe(Al)O3-delta perovskite and monoclinic SrAl2O4-based phases, occurs via different mechanisms in comparison to the dry methane interaction with the lattice oxygen. The catalytic behavior of powdered (SrFe)(0.7)(SrAl2)(0.3)O-z, studied by temperature-programmed reduction in dry CH4 at 523-1073 K, is governed by the level of oxygen nonstoichiometry in the crystal lattice of the perovskite component and is qualitatively similar to that of other perovskite-related ferrites, such as Sr0.7La0.3Fe0.8Al0.2O3-delta. While extensive oxygen release from the ferrite lattice at 700-900 K leads to predominant total oxidation of methane, significant selectivity to synthesis gas formation, with H-2/CO ratios close to 2, is observed above 1000 K, when a critical value of oxygen deficiency is achieved. The steady-state oxidation over dense membranes at 1123-1223 K results, however, in prevailing total combustion, particularly due to excessive oxygen chemical potential at the membrane surface. In combination with surface-limited oxygen permeability, mass transport limitations in a porous layer at the membrane permeate side prevent reduction and enable stable operation of (SrFe)(0.7)(SrAl2)(0.3)O-z membranes under air/methane gradient. Taking into account the catalytic activity of SrFeO3-delta-based phases for the partial oxidation of methane to synthesis gas and the important role of mass transport-related effects, one promising approach for membrane development is the fabrication of thick layer of porous ferrite-based catalyst at the surface of dense (SrFe)(0.7)(SrAl2)(0.3)O-z composite.
keywords
SYNTHESIS GAS; THERMOMECHANICAL PROPERTIES; MEMBRANE REACTOR; ION-TRANSPORT; DRY METHANE; OXYGEN; CONVERSION; SYNGAS; SURFACE; PEROVSKITES
subject category
Chemistry; Physics
authors
Yaremchenko, AA; Kharton, VV; Valente, AA; Veniaminov, SA; Belyaev, VD; Sobyanin, VA; Marques, FMB
our authors
Aleksey Yaremchenko
Principal Researcher
Anabela Tavares Aguiar Valente
Principal Researcher
Fernando Manuel Bico Marques
Full professor