Kinetics and mechanism of pyruvic acid degradation by ozone in the presence of PdO/CeO ₂

This work investigated the catalytic ozonation of pyruvic acid (PA) in the presence of PdO/CeO ₂ (i.e., Pd deposited on CeO ₂) with focus on the kinetics of PA degradation at different catalyst dosages, reaction pHs and temperatures, as well as the possible catalytic mechanism. By analyzing the kinetic contributions of heterogeneous and homogeneous reactions to PA degradation, it was found that the presence of PdO/CeO ₂ significantly enhanced the degradation of PA compared to ozonation alone especially at acidic pHs (3.0-6.0). The catalytic degradation of PA took place on the catalyst surface, which was irrelevant to hydroxyl radicals in the bulk solution. Temperature exhibited an insignificant effect on PA degradation in the range of 12-32°C. Synergic effect was observed between PdO and CeO ₂ on aqueous ozone decomposition, catalytic ozonation, and adsorption of PA with PdO/CeO ₂. Ozone and PA were first adsorbed and then activated by the active sites on catalyst surface, and thus becoming more reactive to each other. The influence of phosphate on catalytic ozonation of PA corroborated that the adsorption of PA onto PdO/CeO ₂ was a critical step for the overall reaction. ATR-FTIR analysis showed that PdO/CeO ₂ possessed more Lewis acid sites than CeO ₂, and Pd tended to be the main active sites. Neither OH nor O ₂ ^- was involved in the catalytic ozonation of PA as respectively substantiated by the experiments with t-BuOH (as OH scavenger) and nitro blue tetrazolium (as O ₂ ^- indicator).