Silica templating of a water-in-oil (w/o) microemulsion system containing HAuCl4 results in gold nanoparticles of sizes around 3 nm confined in hollow silica nanospheres. The size of the gold nanocatalyst is stable to high temperature calcination. Its catalytic activity toward CO oxidation is very stable after repeated use and long-time storage. The reaction can be controlled by a corking design based on capillary condensation of water vapor for corking the mesopores on the shell. At higher temperature or low water vapor pressure, pores open after vapor evaporation and water promotes the CO oxidation. The corking and uncorking mechanism of the yolk-shell type nanoreactor is reversible.
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