NOVELTY - Preparing a deposition of metal nanoparticles, or its alloy with at least one other metal on a porous surface of a substrate, comprises exposing the porous surface of the substrate previously heated to a vapor phase containing metal precursors to increase the pressure in the chamber, injecting a reactive gas into the chamber under vacuum and optionally repeating the above steps. The metal is metal from columns VIIIB and IB (8, 9, 10 and 11) of the Periodic Table elements, from a precursor of the metal or from a precursor of the metal and at least one precursor of another metal.    USE - The substrate is useful: for catalyzing at least one chemical reaction, which is a gas phase reaction, an oxidation reaction, preferably selective, such as oxidation of methanol, epoxidation of olefins, oxidation of hydrocarbons, oxidation of carbon monoxide, oxidation of nitrogen oxides (NOx), combustion of the carbonaceous particles comprising carbon or soot materials, combustion of the particles contained in the gases emitted by the diesel engines, nitrogen dioxide (N2O) decomposition, reforming of light alcohols such as methanol and ethanol, or a reformed gas for e.g. in fuel cells, or reaction for controlling air pollution, and a liquid phase reaction, in aqueous phase; for simultaneously catalyzing an oxidation reaction of carbon monoxide and oxidation reaction of the nitrogen oxides; and in thermoelectric recovery device for the treatment of diesel smoke, in a device for preventing clogging of an exhaust gas eecirculation valve and in a device for preventing the fouling of heat exchangers for the treatment of industrial flue gases (all claimed). The substrate is useful as membranes for hydrogen permeation, to catalyze the hydrogenation/dehydrogenation reactions, or to catalyze other reactions occurring in fuel cells.    ADVANTAGE - The method is capable of deposition of metal nanoparticles on a surface of a substrate without requiring high vacuum, with primary education vacuum, low pollution and great flexibility hence depositing all metals of the columns VIII B and IB (8, 9, 10, and 11) of the periodic Classification of the elements, and with high dispersion of the particles and their low size, in easy manner. The method: strongly increases the catalytic effectiveness by the increase in several orders of magnitude amongst active sites and by the formation of alloys and composites which are defined more easily than by traditional methods of preparation; allows a significant lowering of the level of loading out of catalyst, which can be 10 times inferior compared to a traditional method such as the impregnation and thus a lowering of the cost of the devices, preferably using noble metals; and is cost-effective due to the use of an alloy, for e.g. a silver alloy and a noble metal. The substrates can define as nanostructured catalysts have a very high catalytic activity even at low temperature. The substrate containing a deposit of two families of alloy metal has low temperatures of activation.    DETAILED DESCRIPTION - Preparing a deposition of metal nanoparticles, or its alloy with at least one other metal on a porous surface of a substrate, comprises exposing the porous surface of the substrate previously heated to a vapor phase containing metal precursors to increase the pressure in the chamber, injecting a reactive gas into the chamber under vacuum and optionally repeating the above steps. The metal is metal from columns VIIIB and IB (8, 9, 10, and 11) of the Periodic Table elements, from a precursor of the metal or from a precursor of the metal and at least one precursor of another metal. The substrate is placed in chemical vapor deposition chamber under vacuum. An INDEPENDENT CLAIM is included for the substrate comprising a porous surface provided with a metal nanoparticle deposition or an alloy of the metal with at least one other metal.