Subcritical Water Regeneration of Supported Ruthenium Catalyst Poisoned by Sulfur

A titania-supported ruthenium (Ru/TiO2) catalyst was effective for the gasification of lignin to methane, carbon dioxide, and hydrogen in supercritical water. For the Ru/TiO2 catalyst poisoned by sulfur (S−Ru/TiO2), the overall gas yield decreased and the tetrahydrofuran-insoluble products (namely, char) were slightly formed in supercritical water gasification. After subcritical water treatments of the S−Ru/TiO2 catalyst at 523 and 573 K, its gasification activity was found to be higher than that without the treatment. On the other hand, the treatment of the S−Ru/TiO2 catalyst in supercritical water at 673 K showed lower activity than that in subcritical water. X-ray photoelectron spectroscopy analysis showed that three-fourths of the amount of sulfur was removed from the catalyst surface after the subcritical water treatment. It was concluded that deactivated catalysts poisoned by sulfur species could be regenerated by the removal of the sulfur by the treatment with subcritical water.