Palladium Nanoparticles Supported on Activated Carbon (C) for the Catalytic Hexavalent Chromium Reduction

Abstract

Hexavalent chromium is widely used in industry and causes human health and environmental problems due to its extremely toxic properties. On the contrary, trivalent chromium is necessary for living ecosystems. Therefore, reducing hexavalent chromium to trivalent chromium is the best strategy for detoxifying hexavalent chromium. Pd(0)@C nanocatalyst was prepared by a simple impregnationreduction method in solution under mild conditions at 298 K and was identified by XPS, XRD, TEM, TEM-EDX, HR-TEM, and ICP-OES analyses. TEM results showed that very well-dispersed Pd nanoparticles were formed on the C surface (mean particle sizes 3.98 +/- 0.24 nm). The catalytic performance of Pd(0)NPs impregnated on cheap and easily available commercial activated carbon were tested as heterogeneous nanocatalysts in the catalytic reduction of hexavalent chromium in the medium of formic acid, which is a good reducing agent, and sodium formate as the promoter at 298 K. It was determined that the formed Pd(0) nanoclusters could successfully reduce Cr(VI) to Cr(III) with high selectivity (similar to 97%) in formic acid and sodium formate solution under mild conditions. It was also observed that the Pd(0)@C catalyst retained a significant (>75%) initial activity even after the 5th use. In addition, the kinetic studies of the catalytic reduction reaction of Cr(VI) catalyzed by Pd(0)@C nanoparticles were investigated depending on the substrate [Cr2O72-], catalyst [Pd(0)@C], sodium formate [HCOONa], formic acid [HCOOH] concentrations, and temperature parameter. From the rich kinetic data obtained, the nature of the velocity equation was explained, and the activation parameters were calculated.