Pt/C stabilization for catalytic wet-air oxidation: Use of grafted TiO2

The wet-air oxidation (WAO) process is effective in converting organic pollutants in wastewater to innocuous carbon dioxide. Supported Pt catalysts, particularly Pt/C, are effective but unstable. A novel catalyst, Pt on TiO2-grafted carbon (Pt/TiO2-C), has been developed for WAO. This catalyst is characterized by high activity and stability in WAO processes. Using transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), and Fourier transform infrared (FTIR) spectroscopy, the fresh and aged Pt/C catalysts were characterized, and the mechanism of catalyst deactivation was elucidated. The average Pt cluster size increased from about 2 to 10 nm after WAO of methanol in water at 220 °C for 200 h. These results indicate that Pt/C catalyst was deactivated due to migration and aggregation of the Pt clusters into large Pt particles. The increase in the content of oxygen-containing groups and carbonate species, as characterized by FTIR spectra in the aged catalyst, further suggests that the oxidation of carbon surface decreases the affinity between Pt and the carbon support, leading to extensive Pt aggregation. Thus, TiO2 was grafted on to the carbon support to anchor and keep Pt from migrating and agglomerating, thereby obtaining a stable Pt/TiO2-C catalyst. The efficacy of TiO2 grafted on activated carbon in stabilizing the Pt/C catalyst was demonstrated in long-term catalytic performance tests. The efficacy of TiO2 in anchoring and maintaining the Pt clusters in small ensembles were further demonstrated by characterizing the Pt–TiO2 interactions and the morphology of Pt clusters using EXAFS.