AIChE Journal, Vol.64, No.8, 3141-3150, 2018
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 degrees 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% H-2 conversion, 88% selectivity) at 850 degrees C over 50 redox cycles. In series with a Cr2O3/Al2O3 ethane dehydrogenation catalyst, Na2WO4/CaMnO3 combusted 84% of H-2 produced while limiting COx 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. (C) 2018 American Institute of Chemical Engineers
Keywords:chemical looping;oxidative dehydrogenation;redox catalyst;selective hydrogen combustion;olefin