Synthesis and Activity of Heterogeneous Pd/Al2O3 and Pd/ZnO Catalysts Prepared from Colloidal Palladium Nanoparticles

Heterogeneous catalysts composed of Pd nanoparticles on zinc oxide (ZnO) and aluminum oxide (Al2O3, alumina) were synthesized and tested for catalytic activity. Palladium nanoparticles were synthesized via solution-precipitation methods and deposited on aluminum oxide and zinc oxide supports. The particles were synthesized by decomposing a palladium precursor (Pd(Mes)(2)) in a solution of trioctylphosphine [TOP route] or palladium acetate (Pd(OAc)(2)) in a solution of octylamine [amine route] at 300 degrees C. The particles were washed and suspended in hexane, whereupon they were deposited on an oxide powder. Supported nanoparticle powders were subjected to CO oxidation tests to determine catalytic activity. Particle sizes ranged from 2.4 +/- 0.4 nm average diameter when prepared using trioctylphosphine to 4 +/- 1 nm using the amine route. No significant size change was observed after removal of the surfactant and catalytic testing by CO oxidation. The highest conversion of CO to CO2 occurred with a calcined sample, indicating that the removal of surfactant increases activity.