In general, the catalytic activity of noble metal nanoparticles is related to their particle size. If the size is larger enough, can they keep the catalytic activity.
Kindly remember the good old Ostwald process for the synthesis of NO ( finally nitric acid) using platinum as catalyst. Here the platinum catalyst size is beyond nano and much larger than your estimate . Size does influence activity but one has to find out the optimum size for a specific reaction catalyzed by noble or any other metal
Noble metasl always remain catalysts, provided that you have a high enough available surface area. Therefore, the bigger the particle size, the lower the surface area, and the more metal you need, as most of this metal won't be available. Hence the interest of having as small particles as possible, so that as many metal atoms as possible are located at the surface and can act as catalyst. This is extremely important because of the cost of such metals, and when really nano, a very low amount is enough for having a good catalyst.
Alain
Very true answer.A note to add for reactivity of nano metal. Iron powder ( not noble) in normal mesh size gets oxidised by air which for bigger iron chunk we call corrosion. If nano iron can be prepared by thermal decomposition of iron pentacarbonyl then such nano iron catches fire under exposure to air.
To Mr. Sabyasachi Sarkar
Moreover, we synthesized iron-cobalt and iron-nickel nanoparticles by chemical reduction of metal-salt from aqua-solution. When the particles was in contact with air the ignition of its was observed.
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