Palladium nanoparticles supported on aluminum oxide (Al2O3) for the catalytic hexavalent chromium reduction

While Cr(VI), a hazardous industrial waste, is an acute toxic, carcinogenic, and proven mutagenic pollutant, Cr(III) is thought to be an essential element for living things. In this study, Pd(0)@Al2O3 nanoclusters supported on Al2O3 were reproducibly prepared in aqueous solution at 25 °C by a simple impregnation-reduction method. The results showed that Pd(0)@Al2O3 nanoclusters with average particle size of 3.01 ± 0.19 nm were formed, well dispersed over the Al2O3 surface. The Al2O3-supported Pd(0)@Al2O3 nanoclusters were used as heterogeneous nanocatalysts in the catalytic reduction of Cr(VI) in formic acid medium, which is a good reducing agent under mild conditions. It has been observed that catalyst Pd(0)@Al2O3 can catalyze the catalytic reduction of Cr(VI) with high selectivity (~ %99) and efficiency (TOF) (138 mol Cr2O72−/mol Pd min.). More importantly, the exceptional stability of the Pd(0)@Al2O3 nanocatalyst against flocculation, leaching, and CO poisoning showed that this catalyst is a reusable catalytic material in the catalytic reduction reaction of Cr(VI). It was observed that the Pd(0)@Al2O3 catalyst maintained a significant (> 84%) initial TOF value even after the 5th use. The Pd(0)@Al2O3 nanocatalyst was identified by advanced analytical methods (XPS, XRD, TEM, TEM–EDX, HR-TEM, ICP-OES). In addition, for the kinetic data of the catalytic reduction reaction of Cr(VI) catalyzed by Pd(0)@Al2O3, the rate equation and Ea, ΔH#, and ΔS# activation parameters were derived depending on the [catalyst], [Cr2O72−], [HCOOH], and [HCOONa] concentrations and temperature.