Accelerating Catalytic Oxyanion Reduction with Inert Metal Hydroxides

Adding Cr^III or Al^III salts into the water suspension of platinum group metal (PGM) catalysts accelerated oxyanion pollutant reduction by up to 600%. Our initial attempts of adding K₂Cr^VIO₄, K₂Cr^VI₂O₇, or KCr^III(SO₄)₂ into Pd/C enhanced BrO₃^- reduction with 1 atm H₂ by 6-fold. Instrument characterizations and kinetic explorations collectively confirmed the immobilization of reduced Cr^VI as Cr^III(OH)₃ on the catalyst surface. This process altered the ζ-potentials from negative to positive, thus substantially enhancing the Langmuir-Hinshelwood adsorption equilibrium constant for BrO₃^- onto Pd/C by 37-fold. Adding Al^III(OH)₃ from alum at pH 7 achieved similar enhancements. The Cr-Pd/C and Al-Pd/C showed top-tier efficiency of catalytic performance (normalized with Pd dosage) among all the reported Pd catalysts on conventional and nanostructured support materials. The strategy of adding inert metal hydroxides works for diverse PGMs (palladium and rhodium), substrates (BrO₃^- and ClO₃^-), and support materials (carbon, alumina, and silica). This work shows a simple, inexpensive, and effective example of enhancing catalyst activity and saving PGMs for environmental applications.