Manganese-containing redox catalysts for selective hydrogen combustion under a cyclic redox scheme

Selective hydrogen combustion (SHC) in the presence of light hydrocarbons was demonstrated with a series of Mn-containing mixed oxide redox catalysts in the context of a chemical looping-oxidative dehydrogenation scheme. Unpromoted and 20 wt % Na₂WO₄-promoted Mg₆MnO₈, SrMnO₃, and CaMnO₃ exhibited varying SHC capabilities at temperatures between 550 and 850°C. Reduction temperature of unpromoted redox catalysts increased in the order Mg₆MnO₈ < SrMnO₃ < CaMnO₃. Promotion with 20 wt % Na₂WO₄ resulted in more selective redox catalysts capable of high-temperature SHC. XPS analysis revealed a correlation between suppression of near-surface Mn and SHC selectivity. Na₂WO₄/CaMnO₃ showed steady SHC performance (89% H₂ conversion, 88% selectivity) at 850°C over 50 redox cycles. In series with a Cr₂O₃/Al₂O₃ ethane dehydrogenation catalyst, Na₂WO₄/CaMnO₃ combusted 84% of H₂ produced while limiting CO_x yield below 2%. The redox catalysts reported can be suitable for SHC in a cyclic redox scheme for the production of light olefins from alkanes.