Huixia Luo

Natural Gas to Fuels and Chemicals: Improved Methane: Aromatization in an Oxygen-Permeable Membrane Reactor

Adding value with membranes: Improved methane aromatization was achieved by using an oxygen-permeable membrane. The resulting membrane reactor shows a superior methane conversion and a higher resistance towards catalyst deactivation.

B-site La-doped BaFe0.95−xLaxZr0.05O3−δ perovskite-type membranes for oxygen separation

Partial La-substitution for Fe on the B-site of the perovskite BaFe0.95−xLaxZr0.05O3−δ (BFLZ) was achieved by applying a sol–gel synthesis method. The highest La content in BFLZ for the formation of a pure cubic perovskite structure without any detectable impurities is about x = 0.04. It is found for the first time that the introduction of La on the B-site of a mixed oxide stabilizes the cubic structure. Furthermore, the formation of the cubic structure of BFLZ increases significantly the oxygen permeability. The maximum oxygen permeation flux is found for a La-content of x = 0.04 with the largest volume of the cubic unit cell, reaching 0.63 and 1.24 cm3 (STP) min−1 cm−2 for a 1.1 mm thick membrane at 750 and 950 °C, respectively. This finding is in complete agreement with the XRD structure analysis, showing that the highest B-site La-substitution of BFLZ under conservation of the pure cubic perovskite phase without forming any foreign phase was about x = 0.04. For BFLZ with x > 0.04, the secondary phase Ba6La2Fe4O15 forms increasingly and the oxygen permeation flux decreases. The influence of the sweep gas flow rates on the oxygen permeation flux and the oxygen ionic conductivity were found to be in good agreement with the Wagner theory, indicating the oxygen ion bulk diffusion as a rate-limiting step of oxygen transport. Stable oxygen permeation fluxes were obtained during the long-term oxygen permeation operation of the BFLZ (x = 0.04) membrane over 170 h at 750 and 950 °C, respectively.

A CO2-stable reduction-tolerant Nd-containing dual phase membrane for oxyfuel CO2 capture

We report a novel CO2-stable reduction-tolerant dual-phase oxygen transport membrane 40 wt% Nd0.6Sr0.4FeO3−δ–60 wt% Ce0.9Nd0.1O2−δ (40NSFO–60CNO), which was successfully developed by a facile one-pot EDTA–citric sol–gel method. The microstructure of the crystalline 40NSFO–60CNO phase was investigated by combined in situ X-ray diffraction (XRD), scanning electron microscopy (SEM), back scattered SEM (BSEM), and energy dispersive X-ray spectroscopy (EDXS) analyses. Oxygen permeation and long-time stability under CO2 and CH4 atmospheres were investigated. A stable oxygen flux of 0.21 cm3 min−1 cm−2 at 950 °C with undiluted CO2 as sweep gas is found which is increased to 0.48 cm3 min−1 cm−2 if the air side is coated with a porous La0.6Sr0.4CoO3−δ (LSC) layer. All the experimental results demonstrate that the 40NSFO–60CNO not only shows good reversibility of the oxygen permeation fluxes upon temperature cycling, but also good phase stability in a CO2 atmosphere and under the harsh conditions of partial oxidation of methane to synthesis gas up to 950 °C.

An Efficient Oxygen Activation Route for Improved Ammonia Oxidation through an Oxygen-Permeable Catalytic Membrane

Upon using a reactant/oxygen mixture as co‐feed in partial oxidation, adsorbed surface molecular oxygen species can cause low selectivity. We propose a concept different from the conventional co‐feed partial oxidation process in packed‐bed reactors. In this new configuration, the activation of oxygen is separated from the catalytic oxidation by using an oxygen‐permeable membrane to suppress the formation of nonselective surface molecular oxygen species. A continuous flux of lattice oxygen through the membrane allows highly selective partial oxidation. In the oxidation of ammonia to NO, the NO selectivity was improved from 77 to 95 % if a La0.6Sr0.4Co0.2Fe0.8O3–δ oxygen‐permeable catalytically active membrane was used at 850 °C instead of a co‐feed fixed bed reactor.