Methane oxidation over mixed-conducting SrFe(Al)O3-delta-SrAl2O4 composite.
The steady-state CH4 conversion by oxygen permeating through mixed-conducting (SrFe)0.7(SrAl2)0.3Oz 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)0.3Oz, 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 H2/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)0.3Oz 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)0.3Oz composite.
Yaremchenko
A A
AA
Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193, Aveiro, Portugal.
Kharton
V V
VV
Valente
A A
AA
Veniaminov
S A
SA
Belyaev
V D
VD
Sobyanin
V A
VA
Marques
F M B
FM
D017607:Aluminum Compounds / Q000737:chemistry*; D002384:Catalysis; D004553:Electric Conductivity; D007501:Iron / Q000737:chemistry*; D008697:Methane / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010316:Particle Size; D013324:Strontium / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
D017607:Aluminum Compounds; D007501:Iron; D008697:Methane; D010100:Oxygen; D013324:Strontium