Catalytic activation of a solid oxide in electronic contact with gold nanoparticles.

Although inert in its bulk form, nanostructured gold supported on oxides has been found to be catalytically active. In many cases, the oxide promotes the activity of Au. It is now shown that in turn, nanoscale Au particles can chemically activate the solid oxide. Specifically, it was discovered that 4 nm Au nanoparticles deposited on zinc oxide catalyze the transformation of the oxide into the sulfide in the presence of an organosulfur species. Contact of the oxide with Au nanoparticles lowers the activation barrier for the solid-state reaction by approximately 20 kJ mol(-1), allowing the reaction to be achieved closer to ambient temperatures. Electron transfer from oxygen vacancies to Au nanoparticles is proposed to generate acidic sites on the surface of the zinc oxide, resulting in the enhanced reactivity of the oxide. Knowledge of such electronic interactions between the noble metal and oxide can be exploited for engineering reactive heterostructures for low-temperature pollutant sorption and hydrocarbon processing.

Co-operativity in a nanocrystalline solid-state transition.

Co-operativity is a remarkable phenomenon mostly seen in biology, where initial reaction events significantly alter the propensity of subsequent reaction events, giving rise to a nonlinear tightly regulated synergistic response. Here we have found unique evidence of atomic level co-operativity in an inorganic material. A thousand-atom nanocrystal (NC) of the inorganic solid cadmium selenide exhibits strong positive co-operativity in its reaction with copper ions. A NC doped with a few copper impurities becomes highly prone to be doped even further, driving an abrupt transition of the entire NC to the copper selenide phase, as manifested by a strongly sigmoidal response in optical spectroscopy and electron diffraction measurements. The examples presented here suggest that cooperative phenomena may have an important role in the solid state, especially in the nucleation of new chemical phases, crystal growth, and other materials' transformations.

A regenerable oxide-based H2S adsorbent with nanofibrous morphology.

Hydrogen sulphide is found in raw fuels such as natural gas and coal/biomass-derived syngas. It is poisonous to catalysts and corrosive to metals and therefore needs to be removed. This is often achieved using metal oxides as reactive adsorbents, but metal oxides perform poorly when subjected to repeated cycles of sulphidation and re-oxidation as a result of complex structural and chemical changes. Here, we show that Zn-Ti-O-based adsorbents with nanofibrous morphology can sustain their initial reactivity and sulphur removal capacity over multiple regeneration cycles. These nanostructured sorbents offer rapid reaction rates that overcome the gas-transport limitations of conventional pellet-based sorbents and allow all of the material to be used efficiently. Regeneration can be carried out at the same temperature as the sulphidation step because of the higher reactivity, which prevents sorbent deterioration and reduces energy use. The efficient regeneration of the adsorbent is also aided by structural features such as the growth of hierarchical nanostructures and preferential stabilization of a wurtzite phase in the sulphidation product.