The gas phase reduction is effective for obtaining nanopowders of refractory (Mo, W) and transition metals, and is carried out by hydrogen or gaseous hydrogen-containing compounds at temperatures up to 230ºC. The advantages of the method include a low impurity content and narrow powder particle size distribution. The same method, but with solid phase reduction of metal, is used to produce metal catalysts. In this case a porous material (silica gel, zeolite, etc.) is impregnated with a true or colloidal solution of hydroxide or another compound of the desired metal; then the impregnated porous carrier is dried and calcined in hydrogen flow to reduce the deposited particles to the metal. As a result, catalytically active small metal particles are formed in the pores of the carrier. Heating the composite of nickel hydroxide and ortho-silicic acid at 450-750ºC in a hydrogen flow allows the production of stabilised Ni nanoparticles sized between 5-10 nm (at 550ºC) and 15-25 nm (at 750ºC).

The liquid phase reduction of metals is carried out at temperatures of up to 130ºC in aqueous media and up to 230ºC in non-aqueous media, and, in essence, it is the method of obtaining colloidal nanoparticles. The reducing agents used in this case include hydrazine, alkali metal tetrahydroborates, hydronitric and N-B-H compounds, hypophosphite, sodium citrate, formaldehyde, hydroquinone, menthol, alcohols and other substances. Protective colloids and stabilizers (gelatin, starch, polyvinyl alcohol, pyridine, phenanthroline, etc.) are introduced into the liquid medium to prevent agglomeration of nanopowders. The size of the resulting colloidal nanoparticles does not exceed 10-15 nm.