Catalytic supercritical water oxidation of pyridine: Comparison of catalysts

The catalytic supercritical water oxidation (CSCWO) of pyridine in the presence of several catalysts such as Pt/gamma-Al2O3, MnO2/gamma-Al2O3, and MnO2/CeO2 was studied. Experiments conducted with alpha-Al2O3 and gamma-Al2O3 confirmed the inertness of these catalysts toward SCWO of pyridine. Complete conversions were obtained at 370 degrees C in the presence of platinum catalyst. Ammonia and nitrogen oxides mere not observed. Platinum catalyst favored the formation of nitrate ions and nitrous oxide whereas the MnO2 catalysts favored the formation of nitrogen and nitrate ions. The rate of pyridine oxidation was modeled assuming power-law kinetics. The results indicate that the two manganese catalysts performed similarly. The power-law analysis indicates that the rate of oxidation is first order with respect to pyridine on the manganese catalyst whereas it was found to be second order for the platinum catalyst. Two different reaction mechanisms are proposed to describe the experimental observations.