TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The reducing agent is hydrogen, hydrogen sulfide, formaldehyde, sodium borohydride, hydrazine and/or hydroxylamine (preferably gaseous hydrogen).Preferred Method: The reduction is carried out under pressure, where the pressure controls the metal particle size.(I) is adsorbed when it is in mixture and is vented.When (I) and (S1) are exposed to the fluid, at least some or all of (I) dissolves in the fluid.The method involves:(A) adding (S1) and (I) to a reactor;(B) adding the supercritical fluid to the reactor to form a mixture with (I);(C) allowing (I) to remain in contact with the substrate to deposit dispersed organometallic onto the substrate;(D) venting the reactor, thus adsorbing (I) onto (S1);(E) adding the gaseous reducing agent to the reactor; and(F) contacting the reducing agent and organometallic until the organometallic is reduced to dispersed metal particles.The method further involves reducing the dispersed (I) to dispersed metal particles with the reducing agent under pressure conditions effective to form the desired particle size thus forming a supported particulate catalyst with controlled metal particle size.    TECHNOLOGY FOCUS - METALLURGY - Preferred Components: The metal particles are nanoparticles of less than 10 (preferably 0.5 - 10, especially 0.5 - 5) nm in average diameter, and are noble metal particles selected from platinum, iridium, osmium, rhenium, ruthenium, rhodium, palladium, vanadium, chromium, gold, silver, nickel and/or cobalt or their alloy (preferably platinum, silver, ruthenium).The metal particles are mixed metal particles.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: (S1) is a carbonaceous material comprising carbon black, graphite, nanocarbons, fullerenes and/or finely divided carbon (preferably carbon black).(I) is 1,5-cyclooctadiene dimethyl platinum (Pt(COD)Me2), (1,5-cyclooctadiene) (hexafluoroacetylacetonato) silver (Ag(COD)hfac), ruthenium acetylacetonate (Ru(acac)3) and/or silver acetylacetonate (Ag(acac)).The fluid comprises carbon dioxide, ethane, ethylene, propane, propylene, chlorotrifluoromethane or ammonia (preferably carbon dioxide).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The reducing agent is hydrogen, hydrogen sulfide, formaldehyde, sodium borohydride, hydrazine and/or hydroxylamine (preferably gaseous hydrogen).Preferred Method: The reduction is carried out under pressure, where the pressure controls the metal particle size.(I) is adsorbed when it is in mixture and is vented.When (I) and (S1) are exposed to the fluid, at least some or all of (I) dissolves in the fluid.The method involves:(A) adding (S1) and (I) to a reactor;(B) adding the supercritical fluid to the reactor to form a mixture with (I);(C) allowing (I) to remain in contact with the substrate to deposit dispersed organometallic onto the substrate;(D) venting the reactor, thus adsorbing (I) onto (S1);(E) adding the gaseous reducing agent to the reactor; and(F) contacting the reducing agent and organometallic until the organometallic is reduced to dispersed metal particles.The method further involves reducing the dispersed (I) to dispersed metal particles with the reducing agent under pressure conditions effective to form the desired particle size thus forming a supported particulate catalyst with controlled metal particle size. EXAMPLE - CDX-975Trade Mark carbon black (54.6 mg) and 1,5-cyclooctadiene dimethyl platinum (Pt(COD)Me2) (27.7 mg) were added to a stainless steel reactor and sealed. The reactor was then placed in a constant temperature bath at 60degreesC. Coleman grade carbon dioxide (11.51 g) was added to the reactor to a final pressure of 2000 psi giving a 0.24 wt % solution of Pt(COD)Me2. The sample was allowed to soak, with stirring, for 23 hours, after which the solution was vented through an activated carbon bed to atmospheric pressure. Hydrogen was then added to the reactor via a pressure drop of a high-pressure manifold to an effective pressure of 600 psi for 1 hour at 60degreesC. Ashing by thermogravimetric analysis gave a final platinum loading on carbon black of 15.9%.