Selective extraction of supported Rh nanoparticles under mild, non-acidic conditions with carbon monoxide

Owing to their limited supplies, recycling of precious metals, especially rhodium, is vital to sustain the growth of certain nanotechnologies. Here we report a mild, efficient, and selective method for rhodium recovery that relies on the use of carbon monoxide to extract rhodium nanoparticles on various supports in polar solvents. Unlike the traditional recycling technologies, this method operates at low temperature and does not require strong acids. Moreover, the CO-induced leaching is complimentary to leaching by acids in terms of selectivity toward rhodium versus other precious metals and results in metal recovery in the form of reduced metallic clusters. The method performs best on freshly reduced surfaces and can be promoted by the addition of tertiary amines. Besides CO gas, formic acid can also be used as a leachant by decomposition to produce CO by Rh catalysis. The concept of CO-induced leaching could be applied to the extraction of rhodium from nuclear waste and extended to modify rhodium nanoparticle size and composition.