Synthesis of Pd/(MnO₂@PANI) Catalyst and Its Study on the Reduction of Cr(VI)

Liquid-phase catalytic hydrogenation is a non-polluting and highly efficient technique for the reductive removal of hexavalent chromium from water, which has the advantages of a simple device, easy operation, mild, and green reaction conditions without secondary pollution, and high efficiency. In this study, the loaded catalysts Pd/(MnO₂@PANI) and Pd/MnO₂ were synthesized by the precipitation deposition method, and the composition and morphology of the catalysts were analyzed by using ICP, XRD, XPS, and TEM characterization. The effects of different catalysts, catalyst dosage, initial Cr(VI) concentration, pH value, and palladium loading on the Cr(VI) reduction reaction were also investigated using Pd/(MnO₂@PANI) and Pd/MnO₂ as catalysts and formic acid as hydrogen source. The results showed that the reduction of 1 mM Cr(VI) was 99.4% after 120 min at pH 2 and 0.2 g/L catalyst. After 5 consecutive cycles, the reduction rate of Pd/(MnO₂@PANI) remained at 41.5%, and the reduction efficiency of Pd/MnO₂ was only 23.7% after five cycles, which indicated that Pd/(MnO₂@PANI) with polyaniline as the coating layer is a more efficient and stable catalyst that can be recycled for the treatment of Cr(VI) in water. At the same time, after the coating of MnO₂ with polyaniline, the original low toxicity and wide source of MnO₂ will not affect the survival of other plants and animals and will not pollute the environment, and the use of Pd/(MnO₂@PANI) for the reduction of Cr(VI) is of good practical significance, which provides a new solution for the treatment of chromium pollution.