One-pot synthesis of alanine from glycerol without additional H2 over a rutile-supported Ru catalyst

We successfully demonstrate the synthesis of alanine from glycerol and NH3 without additional H2, using a novel Ru-catalyst with optimized metal-support interactions. Three heterogeneous catalysts (Ru/TiO2-Anatase, Ru/ TiO2-Rutile, and Ru/TiO2-P25) were compared, with Ru/TiO2-Rutile showing superior performance, giving complete glycerol conversion with 37 % alanine and 26 % lactate yield after 6 h at 220 degrees C. This performance matches that of state-of-the-art catalysts, but with lower Ru loading (leading to an approximately three-fold higher turnover number) and without external H2 supply. Catalyst characterization revealed that the metal- support interactions in Ru/TiO2-Rutile lead to smaller, well-dispersed Ru nanoparticles (d = 2.3 nm) and lower degree of overlayer TiO2-x formation compared to Ru/TiO2-Anatase, which together contribute to higher Ru accessibility (ARu = 22 %) and thus higher number of active sites per unit mass of Ru, despite the lower surface area of rutile. The reusability of Ru/TiO2-Rutile is strongly influenced by the amount of NaOH utilized in the reaction, with a low NaOH: glycerol ratio (1.1) allowing to recycle the catalyst while largely preserving its activity.