Supercritical water gasification of phenol using a Ru/CeO2 catalyst

Phenols are typical aromatic pollutants and major byproducts of non-catalytic gasification and liquefaction processes. In this work, Ru/CeO2 was prepared and used to catalyze phenol gasification in supercritical water. The catalyst improves carbon efficiency by about 90% at the conditions employed: 0.5 g Ru/CeO2/g phenol catalyst loading at 550 °C with a water density of 0.0979 g/cm3 and a 5 wt% loading of phenol relative to water. This represents a more than 10-fold enhancement of carbon efficiency compared to the noncatalytic case, with CH4 as the major gaseous product. GC-MS results show suppressed formation of dimers, such as dibenzofuran and polycyclic aromatic hydrocarbons (PAHs), which may be caused by the hydrogenation activity of Ru/CeO2. Kinetic modeling of the gasification process gives an activation energy of 84.24 ± 22 kJ/mol and an frequency factor (ln A) of 12.5 ± 2.9 for gaseous product formation, compared to 60 ± 17 kJ/mol and 7.53 ± 2.7 for char formation. Ru/CeO2 is stable in supercritical water at temperatures up to 550 °C, suggesting that a Ru/CeO2 supercritical water gasification system may be a promising method for treating phenols.