Sub-nanocatalysis for Efficient Aqueous Nitrate Reduction: Effect of Strong Metal-Support Interaction.

Magnetic ferroferric oxide-supported bimetallic Pd-In cluster sub-nanoparticles were used for the first time for the catalytic reduction of nitrates. Due to the unique properties of the FeOx support, the PdIn active centers could be highly dispersed in both nano- and sub-nanoscales. A variety of characterizations and the charge density difference model confirm that a strong metal-support interaction exists between the active sites and the support. The PdIn nanoparticles on FeOx show high selectivity toward nitrogen and excellent cyclic activity due to ferromagnetism, which broaden its prospect in practical water treatment. Moreover, the active centers in the sub-nanoscale are used in the nitrate reduction process for the first time and they show a distinct higher activity in denitration. The rate constant for nitrate conversion on PdIn sub-nanoparticles is larger than that for its nanometer counterpart based on the Langmuir-Hinshelwood model. High turnover frequency value and ammonia selectivity are achieved for the small-sized sub-nanocatalyst. The FeOx-supported PdIn nanoparticles and sub-nanoparticles have two application areas in water purification and ammonia recovery, respectively. Density functional theory calculations on the adsorption energies of elemental reactions are also performed, which shed some light on the catalysis mechanism and catalyst design.