Synthesis of Co-Deposited Electroless Pd-Cu Catalyst for Nitrate Reduction

Electrochemical and thermodynamic data obtained from the determination of the corrosion (or open circuit potential or oxidation/reduction) potentials of Cu and Pd in various reducing agents (formaldehyde, hypophosphite and ammonia borane) and their mixtures was used to formulate a stable electroless bath for co-deposition of Cu and Pd on Al₂O₃ substrate. The electrolessly deposited Pd-Cu catalyst was characterized using SEM, EDAX and BET measurements. The Pd-Cu catalyst on alumina was found to be active for nitrate reduction in aqueous solution. The activity and composition of the catalyst increased with electroless plating time up to 30 minutes whereupon the variation of metal composition was minimal. The BET measurement showed that the electroless plating decreases the BET surface area of the catalyst thereby suggesting a macroporous mechanism for nitrate reduction on electroless Pd-Cu catalyst. A comparison of the performance of supported electroless Pd-Cu catalyst versus unsupported, precipitated Pd-Cu-containing particles showed that the unsupported Pd-Cu particles reduced nitrate at a faster rate than the Al₂O₃ supported electroless Pd-Cu catalyst but produced more ammonia. The supported electroless Pd-Cu catalyst converted most of the nitrate in solution into preferred nitrogen gas product rather than ammonia.