Effect of the carbon surface chemistry on the metal speciation in Ru/C catalysts. Impact on the transformation of levulinic acid to γ-valerolactone

• Ru speciation in Ru/C catalysts depends on the oxygen groups on the carbon surface. • The formation of supported Ru 0 is favored upon removal of oxygen groups from carbon. • The Ru speciation affects the H spill over and the formation of protonic acid sites. • The catalytic properties of Ru/C catalysts improve if the carbon surface is cleaner. A set of Ru/C catalysts prepared using a commercial active carbon and a series of carbon materials derived from it (treatment in N 2 flow, at 300, 600 or 900 °C that selectively removes surface oxygen complexes), of similar textural properties and different surface chemistry, were used, without reduction treatment, in the aqueous phase transformation of levulinic acid (LA) to γ-valerolactone (GVL) at 70 °C. The prepared Ru/C catalysts were active, being activity and selectivity strongly dependent on the support surface chemistry. It was confirmed that the supported Ru species became reduced under reaction conditions, and this process was more efficient in catalysts prepared with the heat treated supports, due to the different interactions created between Ru species and the support surface. In a cleaner carbon surface, the anchorage of the Ru species on carbon oxygen groups was limited, and they were more prone to be reduced and to move, forming more defined metallic structures. The carbon surface chemistry determined the Ru speciation (reduced and oxidized species), and the proportion of reduced Ru drived the H spill over process, which was related to the creation of protonic acid sites, proposed to be key point to explain the trend in selectivity to GVL.