Lignin gasification over supported ruthenium trivalent salts in supercritical water

Lignin gasification behavior over unreduced ruthenium trivalent-salts (ruthenium (111) chloride or ruthenium (III) nitrosyl nitrate) supported on titanium oxide and charcoal (RuCl3/TiO2, Ru(NO)(NO3)(3)/TiO2, RuCl3/C, and Ru(NO)(NO3)(3)/C) in supercritical water at 673 K was studied in a batch reactor. The Ru(NO)(NO3)(3)/C and Ru(NO)(NO3)(3)/TiO2 catalysts showed lignin gasification activities as high as a charcoal supported ruthenium catalyst (Ru/C). Characterization by X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS) measurements, and transmission electron microscopy (TEM) revealed that reduced ruthenium metal particles formed during the lignin gasification were smaller in the case of the Ru(NO)(NO3)(3)/C and Ru(NO)(NO3)(3)/TiO2 catalysts, compared with those for the RuCl3/C and RuCl3/TiO2 catalysts. The size of ruthenium metal particles in the case of the Ru/C catalyst did not change by the addition of hydrochloric acid; however, its activity decreased. The RUCl3/C and RuCl3/TiO2 catalysts were less active for the gasification than the Ru(NO)(NO3)(3)/C and Ru(NO)(NO3)(3)/TiO2 catalysts because (i) a large ruthenium metal particles were formed and the number of active metal sites was small and (ii) chloride ions poisoned the active sites of ruthenium metal.