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 > Al2O3 > MgO. At lower temperatures (25-100 degreesC), the trend was ZnO > CaO > Al2O3 approximate to MgO. Core/shell particles, where a thin layer of Fe2O3 was deposited on nanocrystalline CaO, yielded the best results, thus demonstrating another example of transition metal oxide catalysis in solid-gas reactions.