In Situ Raman Spectroscopy of H2 Gas Interaction with Layered MoO3

It is known that the unique layered structure of orthorhombic MoO3 (alpha-MoO3) facilitates the interaction with H-2 gas molecules and that the surface-to-volume ratios of the crystallites play an important role in the process. MoO3 was deposited on a wide variety of transparent substrates using thermal evaporation in order to alter the surface-to-volume ratios of the crystallites. In situ Raman spectroscopy was employed to investigate the interaction between MoO3 and 1% H-2 in both N-2 and synthetic air environments, while incorporating Pd as a catalyst at room temperature. This study confirmed that the layered MoO3 with a high surface-to-volume ratio facilitated the H-2 gas interaction. The Raman spectroscopy studies revealed that the H+ ions mainly interacted with the doubly coordinated oxygen atoms and caused the crystal transformation from the original alpha-MoO3 into the mixed structure of hydrogen molybdenum bronze and substoichiometric MoO3, eventually forming oxygen vacancies and water. It was also found that the presence of O-2 during the H-2 gas exposure caused the recombination of a number of oxygen vacancies and reduced the available surface catalytic sites for H-2.