(500g) Performance and Phase Stability Studies of Gadolinium-Doped Barium Cerate in Oxidative Coupling of Methane and the Impact of Zr Doping

Oxidative coupling of methane (OCM) is a promising technology for the direct conversion of methane to ethylene and ethane (C₂). This process is yet to be commercialized mainly due to the occurrence of undesired reactions that lead to deep oxidation of methane to CO and CO₂. Oxygen ion (O^2-) conducting membrane reactors are currently under investigation as an alternative to conventional packed bed reactors (PBRs) used in OCM. These membrane reactors operate at lower oxygen partial pressures by distributing the oxygen feed, which promotes C₂ product selectivity. A practical design for these membrane reactors would include combining a selective catalyst, preferably O^2− conducting, with an O^2− conducting membrane. In this contribution, we study an O^2− conducting material, gadolinium-doped barium cerate (BaCe_0.8Gd_0.2O_3-δ or BCG), to evaluate its potential applicability as a catalyst and membrane in OCM membrane reactors. From PBR tests, we found that this material was active for OCM, and achieved a maximum C₂₊ yield of ∼14% at 1023 K. Furthermore, a C₂₊ selectivity of ∼90% was obtained at low oxygen partial pressures expected to occur in membrane reactors. Although the C₂₊ yield from this material was stable over 48 h on stream at high methane conversions, X-ray diffraction data showed that the BCG perovskite phase, which is required for its O^2- conductive properties, decomposes into carbonate and oxide phases. We show that this phase instability can be suppressed by doping BCG with Zr without significantly affecting the OCM performance in a PBR.¹

(1) Igenegbai, V. O.; Meyer, R. J.; Linic, S.. Appl. Catal. B Environ. 2018, 230, 29–35.