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 K 2 Cr VI O 4 , K 2 Cr VI 2 O 7 , or KCr III (SO 4 ) 2 into Pd/C enhanced BrO 3 - reduction with 1 atm H 2 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 BrO 3 - 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 (BrO 3 - and ClO 3 - ), 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.