Catalytic Hydrogenation of Nitrate in Water Using a Pd–Cu/Al₂O₃ Catalyst and Dilute H₂ Microbubbles

Abstract: The catalytic hydrogenation of nitrate was performed in solutions containing 20 mg/dm³(Formula presented.) using a Pd–Cu/Al₂O₃ catalyst (synthesized with a Cu/Pd ratio of 0.25) together with microbubbles (radii <50 μm) of 9.4–43.7 % H₂ in N₂. Significant enhancement of the hydrogenation rate was observed due to the application of the microbubbles. The nitrate conversion factors for microbubble hydrogenation were approximately 1.7–3.8 times greater than those obtained using conventional macrobubbles (radii >1500 μm). The application of microbubbles was also effective during hydrogenation in a more concentrated nitrate solution containing 77 mg/dm³(Formula presented.). Graphical Abstract: [Figure not available: see fulltext.]