The catalyst function was achieved in two regions in an oxygen permeation membrane reactor: H2 dissociated and reacted with lattice oxygen or oxygen ions to form H2 O near the membrane surface. The H2 O formed could react with the residual CH4 away from the membrane surface area.
Ba1.0Co0.7Fe0.2Nb0.1O3-δ(BCFN) oxide with perovskite cubic structure was synthesized by solid state reaction method. CO2 corrosion of BCFN membrane was investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), diffuse reflectance infrared Fouriertransformed spectroscopy(DRIFT) and X-ray absorption fine structure spectroscopy(XAFS). Cobalt(Co) K-edge absorption spectra of BCFN annealed in CO2 reveal that the oxidation states of Co in all the samples were larger than +3 and they decreased with the increase of calcination time. At 800℃, 1% CO2 introduced into He could speed up the reduction of Co cations in comparison with pure He. In addition, sulfate ions in the bulk of BCFN membrane preferred to migrate to the surface under CO2 calcination and form monoclinic Ba(CO3)0.9(SO4)0.1besides orthorhombic witherite. Moreover, SEM results indicate that the nucleation and growth of carbonates grains started at the grain boundary of the membrane.
Chengzhang WuHe WangXingxing ZhangYuwen ZhangWeizhong DingChenghua Sun
The effect of Nb doping on the oxygen permeation and stability of SrCo_(0.8)Fe_(0.2)O_(3-δ)(SCFO) was investigated comprehensively.Cubic perovskite phase was formed in SrCo_(0.7)Fe_(0.2)Nb_(0.1)O_(3-δ)(SCFNO).The SCFNO with a thickness of 1 mm had a high level of oxygen permeation flux of 1.4 ml.min^(-1).cm^(-2) at 850 ℃ under air/He gradient.The bulk diffusion is the rate-limiting step in overall oxygen permeation mechanism for SCFNO when the thickness is higher than 1.0 mm.The partial substitution of Nb for Co suppresses the transition of oxygen vacancies order/disorder proven by DSC measurement and enhances the phase stability under low oxygen partial pressure.During long-term tests under low oxygen pressure,the SCFNO exhibites structural stability and stable oxygen permeation.It is proved that substitution of Nb for Co is an effective way to improve the properties of SCFO.
