Rh promoted perovskites for exceptional ?low temperature? methane conversion to syngas

By utilizing lattice oxygen of a reducible metal oxide (a.k.a. redox catalyst), chemical looping reforming (CLR) partially oxidizes methane to syngas without gaseous oxygen. Subsequent to methane partial oxidation (POx), the reduced metal oxide is re-oxidized with air to complete the two-step redox cycle. In essence, CLR accomplishes methane POx without the need for an air separation unit, offering a potentially more efficient route for syngas production. This study investigates Rh promoted and iron/strontium doped CaMnO3 as redox catalysts at relatively low temperatures (<700 °C). These redox catalysts takes advantage of Rh promoter for methane activation as well as the high redox activity of iron/strontium doped CaMnO3. It was determined that Sr and Fe doped CaMnO3 are highly active for methane conversion, showing lattice oxygen extraction of 2.2–4.5 wt.% at 600 °C. However, the syngas selectivities are relatively low, with Sr doped CaMnO3 redox catalysts showing syngas selectivity ˜50% and Fe doped CaMnO3 doped redox catalysts showing syngas selectivity less than 5%. To further increase the syngas selectivity and yield, a reforming catalyst was placed downstream of the chemical looping bed. Under such a sequential bed scheme, 88–96% syngas selectivity was demonstrated for the redox catalysts. Optimization of the reaction conditions showed that a sequential bed composed of Rh promoted CaMn0.75Fe0.25O3 with a downstream reforming catalyst bed is capable of achieving syngas yields above 70% at 600 °C. The relatively low operating temperature and elimination of air separation unit make the redox catalysts and the sequential bed scheme a potentially attractive option for methane conversion. © 2019 Elsevier B.V.