Carbon nanofibers produced by hydrothermal carbonization display remarkable reactivity and the capability for in situ loading with very fine noble-metal nanoparticles of metals such as Pd, Pt, and Au. Large quantities of uniform carbon nanofibers embedded/confined with various kinds of noble-metal nanoparticles can be easily prepared, resulting in the formation of the so-called uniform and well-defined "hybrid fleece" structures. In addition, a general method has been developed to synthesize uniform silica nanotubes embedded/confined with noble-metal nanoparticles by using the "hybrid fleece" consisting of carbon nanofibers loaded with noble-metal nanoparticles as a template. To the best of our knowledge, the filling of silica nanotubes with a dense population of noble-metal nanoparticles has not been demonstrated so far. These hybrid carbon structures embedded with noble-metal nanoparticles in a heterogeneous "fleece" geometry serve as excellent catalysts for a model reaction involving the conversion of CO to CO2 at low temperatures.