Unique Chemical Reactivities of Nanocrystalline Metal Oxides toward Hydrogen Sulfide

Nanocrystalline metal oxides prepared through sol−gel or aerogel syntheses were allowed to react with hydrogen sulfide and compared with microcrystalline commercially available metal oxides. The nanocrystalline metal oxides were found to be considerably more reactive than the commercial samples, as a result of their higher surface areas as well as higher intrinsic reactivities. In some cases, nearly stoichiometric solid−gas reactions took place at selected elevated temperatures, and the oxides exhibited a general reactivity trend of CaO > ZnO > Al 2 O 3 > MgO. At lower temperatures (25−100 °C), the trend was ZnO > CaO > Al 2 O 3 ≈ MgO. Core/shell particles, where a thin layer of Fe 2 O 3 was deposited on nanocrystalline CaO, yielded the best results, thus demonstrating another example of transition metal oxide catalysis in solid−gas reactions.