TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The size of accessible catalytic sites is tuned by adjusting the configurations of the nanostructures. The size of accessible catalytic sites is tuned by adjusting the density of the nanostructures in the disordered array. The size of accessible catalytic sites is tuned by adjusting at least one of the configurations and density of nanostructures in the disordered array. In the catalyst: a majority of the nanostructures are rod-like or coils. The nanostructures comprise silicon dioxide (preferred) or gallium nitride. The nanoparticles comprise a metal, which is gold, platinum or palladium (all preferred), silver, iron, nickel, cobalt, rhodium, ruthenium, copper and/or their alloys. The metal oxide is zinc oxide, titanium dioxide, copper oxide or cobalt oxide. The nanoparticles comprise a metal oxide. The nanostructures are coated with zinc oxide. The nanoparticles are distributed on the substrate and/or nanostructures such that a majority of the nanoparticles are generally isolated from each other. The nanoparticles are distributed on the substrate and/or nanostructures such that there is physical contact between at most about 30% of the nanoparticles. The nanostructures have a cross-sectional dimension of 5-200 nm. The nanoparticles have a cross-sectional dimension of 1-5 nm. The nanostructures comprise a semiconductor material, which is gallium nitride, silicon carbide, titanium dioxide, zinc oxide, aluminum nitride, copper oxide or cobalt oxide. The molecule comprising hydrogen and oxygen comprises: water so that carbon dioxide and hydrogen is produced; or methanol. The substrate and/or at least some of the nanostructures in the disordered array comprise a semiconductor, where the substrate and/or at least some of the nanostructures in the disordered array comprise at least one of the groups consisting of gallium nitride, silicon, silicon carbide, titanium dioxide, zinc oxide, aluminum nitride, copper oxide and cobalt oxide. The disordered array of nanostructures comprises silica nanostructures at least partially coated with a semiconductor. The substrate and/or disordered array of nanostructures comprise a region comprising polycrystalline or single crystal gallium nitride. The nanostructured catalyst comprises nanoparticles having an average cross-sectional dimension of 2-100 (preferably 2-15)nm. The disordered array of nanostructures comprises nanowires, nanosprings, nanorods and/or nanotubes. The substrate and/or disordered array of nanostructures comprise gallium nitride, and the nanoparticles disposed on the substrate and/or disordered array of nanostructures comprise gold. Preferred Method: In the catalyst, a combination of a composition of the nanostructures and a composition of the nanoparticles is selected to tune the activity of the catalyst. The nanostructures are coated with a metal oxide and many of nanoparticles are attached to the metal oxide coating. The method of catalyzing a reaction, comprises: selecting the shape of the size of accessible catalytic sites that can adsorb one or more reactants; selecting a center of the size of accessible catalytic sites that can adsorb one or more reactants; selecting a nanostructure configuration to determine the size of accessible catalytic sites; selecting a density of nanostructures in the disordered array to determine the size of accessible catalytic sites; or selecting a combination of a composition of the nanostructures and a composition of the nanoparticles to catalyze the reaction. The size of the accessible catalytic sites is selected to catalyze a dehydrogenation, hydrogenation or polymerization reaction. In the method for producing hydrogen: at least some of the nanostructures in the disordered array comprise silicon dioxide; a surface area to mass ratio of the nanoparticles on the substrate and/or nanostructures is at least 50 m2/g; disordered array comprises nanostructures having an average cross-sectional dimension of 5-500 (preferably 5-100)nm; the compound capable of generating hydrogen is a cycloalkane, and (gt) bound to the nanostructured catalyst is a dehydrogenated molecular species; the nanoparticles comprise platinum, palladium, ruthenium and/or rhodium; and the step of collecting the hydrogen gas comprises consuming the hydrogen gas in an engine or fuel cell. In the method for storing hydrogen for use in generating energy, the compound produced is cycloalkane.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The cycloalkane is cyclohexane, methylcyclohexane, cis-decalin or trans-decalin. The dehydrogenated compound is a compound of formula (R1-X-X-R1), (R2-XH) or (R3=X), preferably 1,2-dithiolane, dithioparabenzoquinone or 1,4-benzenedithiol (where R2 and R3 are dehydrogenated relative to R1). EXAMPLE - No suitable example given.