Catalytic membrane reactors (CMR) based on H₂-separation membranes can be used to shift the equilibrium of thermodynamically-limited reactions, improving their performance. Industrial processes such as high-pressure steam methane reforming, ammonia cracking, non-oxidative aromatics production, and water gas shift reaction (WGS) could be benefited by these membranes.[1] In these industrial processes, the membrane surfaces are typically exposed to steam, CO₂, CO, H₂S, and hydrocarbons in combination with high temperature, requiring for the membrane materials to be long-term thermo-chemically stable in the mentioned conditions. Stability and operability in H₂S presence is of outstanding importance since many of the membrane ceramic materials are surface poisoned and decomposed even in the presence of several ppm of H₂S. Here, we have assessed and characterize the influence of H₂S on the crystalline structure, lattice composition, surface chemistry and hydrogen transport properties of La_5.4WO_11.1−δ (LWO), one of the reference protonic membrane materials.

The LWO material was submitted to different gas cycles and treatments composed of i) sulfur-free humidified 10% H₂ in N₂ (2.5% H₂O) and ii) humified 10% H₂ with several concentrations of H₂S (⁓2000 and 4000 ppm) in N₂. Measurements were performed from 400 to 700 °C at atmospheric pressure. XRD, XPS, FESEM, WDS, EDS, and FIB-SIMS analyses demonstrated the incorporation of sulfide ions in the crystal lattice, as well as allowed to quantitatively determine how they are distributed among the bulk and the surface. The formation of La₂O₂S was also highlighted after the treatment at 700 °C. The substitution of oxygen by sulfur in the crystal lattice promoted changes in the transport properties. UV-vis spectroscopy and EIS measurements illustrated the enhancement of the electronic conductivity mediated by the concurrent partial reduction of tungsten cations (W⁶⁺), confirmed by XPS. The rise in electronic conductivity led to an increase of the H₂ permeation, which has reached a flux of 0.042 mL cm⁻² min⁻¹ at 700 °C for a ∼770 mm-thick membrane, in contrast with negligible H₂ permeation in H₂S-free conditions.[2]

These findings show the sufficient stability of LWO membranes under H₂S atmospheres, which could stand peaks of H₂S concentration at intermediate temperatures without losing their integrity, circumventing the need of feed stream purification.  They also introduce the possibility of tuning the ambipolar conductivity by incorporating sulfide anions in the LWO oxygen sublattice.