NASA Langley has developed a novel method of depositing metal and metal oxide nanoparticles onto various substrates (see ACS Nano, 3(4), 871–884 ). It is rapid, scalable, and green since it does not require reducing agents or solvents. The process involves first mixing and then heating a metal salt (usually an acetate) with the desired substrate. Heating can be done by conventional thermal or microwave ovens. Conventional thermal processing takes several hours and requires an inert atmosphere, usually nitrogen. With microwave heating, the process is complete in a matter of seconds. The metal or metal oxide nanoparticles have potential use in catalysis. Metal particles on carbon for catalyzing the adsorption of mercury from the effluent of coal-fired power plants has been investigated (Energy & Fuels 23, 1512–1517 .
NASA’s technology involves the development of tailorable catalyst materials by the
deposition of metal and metal oxide nanoparticles on various substrates using a solvent- free method (U.S. Patent 7,704,553). The metal nanoparticles have been deposited on carbon, boron nitride, silica, and glass substrates. Samples containing nano palladium exhibited efficiencies of over 50% in capturing mercury from the effluent of a coal-fired power plant. Similar palladium containing samples were evaluated for their efficiency in catalyzing Suzuki coupling reactions. Conversions of near 100% were achieved at 80 degrees Celsius for 5 minutes. Since these are heterogeneous catalysts, one of the major advantages is the minimum amount of residual metal and metal ions left in the product. With homogeneous (soluble) catalysts, additional purification is required to get the metal content to acceptable levels, resulting in a reduction in product yield. These catalysts are also of interest for use in microreactors for flow chemistry. The technology is described in the previously mentioned patent and in NASA disclosure