Bimetallic (M,M') polymer-protected nanoparticles can be prepared in solution with a range of M:M' ratios. This offers the possibility of ‘rational design' of optimal catalysts for selected reactions. Our work has focused on developing and characterizing a series of palladium and copper colloidal materials for the selective reduction of nitrate in aqueous solution. Metal salts are reduced in 2-ethoxyethanol in the presence of a protecting polymer (PVP, polyvinylpyrrolidone) to form colloid particles containing an alloy of palladium and copper roughly 2-4 nm in diameter. Infrared spectra of adsorbed carbon monoxide offer a qualitative probe of the colloid surface. Transmission electron microscopy provides information on particle size.
The palladium/copper/PVP colloids are used in nitrate reduction experiments to examine the role of changing metal ratios on reaction rate and selectivity. The reactions are carried out in a batch style reactor with continuous hydrogen flow. Nitrate and nitrite levels are monitored by ion chromatography. The results from these ‘homogeneous' bimetallic catalysts will be compared with those from traditional alumina-supported Pd/Cu catalysts.
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