(521bt) Selective H2 Combustion over Alkali Metal-Based Catalysts

Alkali metal formulations (e.g., Li/MgO and NaWO_x) selectively combust hydrogen in mixtures with C₁-C₃ hydrocarbons in the presence of gas phase oxygen at temperatures ≥ 873 K. Heretofore, selective H₂ combustion (SHC) has only been reported on redox-active metal oxides; thus, the alkali metal formulations reported herein represent a new class of selective combustion catalysts. H₂ combustion selectivities exceeding 80% were observed in H₂/CH₄/O₂, H₂/C₂H₆/O₂, and H₂/C₂H₄/O₂ mixtures. The use of N₂O as an oxidant instead of O₂ resulted in higher H₂ combustion selectivities over Li/MgO for all binary mixtures studied, suggesting distinct roles of monoatomic and diatomic oxygen species in SHC over irreducible oxides. Probe molecule reaction studies reporting on whether heterolytic or homolytic C-H and H-H reaction pathways enable selection of combustion pathways that otherwise appear unfavorable and spectroscopic studies that probe the identity of oxygen species on the catalyst surface will be discussed.