Efficient Reduction of Cr (VI) to Cr (III) over a TiO2-Supported Palladium Catalyst Using Formic Acid as a Reductant

Cr (VI) has been considered to be a harmful environmental pollutant due to its toxicity, mobility and strong oxidation. It has become challenging to remove Cr (VI) from wastewater. In this work, a series of supported palladium-based catalysts were synthesized via a facile wet chemical reduction method. Among all the as-synthesized catalysts, Pd/TiO2 (P25) showed the optimized catalytic activity for the reduction of Cr (VI) to Cr (III) using formic acid (HCOOH) as the reductant. More than 99% of K2Cr2O7 (50 mg/L) was reduced completely within 30 min at 25 degrees C. The structural properties of the Pd/TiO2 catalyst (such as particle size, hydrophilicity and stability) and the synergistic effect of metal and support played significant roles in the reduction of Cr (VI) to Cr (III). Meanwhile, several pivotal parameters such as Cr (VI) concentration, catalyst loading, HCOOH concentration and temperature were investigated in detail. Furthermore, this catalyst was also active for the reduction of nitro compounds with HCOOH as the reductant at room temperature. Finally, the reasonable reaction mechanism of the Pd/TiO2/HCOOH system for the reduction of Cr (VI) to Cr (III) was put forward.