Synthesis And Performance Of Novel Palladium Catalysts For The Hydrogenation Of Succinic Acid To γ-butyrolactone

Succinic acid (SUC) is a biobased platform chemical. The selective hydrogenation of SUC to a high value-added product—γ-butyrolactone (GBL) is very important in the field of chemical engineering and resource. However, some challenges also exist in current SUC hydrogenation process, such as severe reaction conditions, high loading of catalysts, poor activity and selectivity. Supported palladium catalysts exhibit high catalytic activity and selectivity in wide hydrogenation reactions. Therefore, two new synthesis routes of palladium catalysts were put forward, namely palladium catalysts incorporated in amino-functionalized core-shell silica spheres (Pd/SiO2-NH2) and palladium catalysts supported on TiO2 nano sheets (Pd/TiO2). These two catalysts display high catalytic activity and selectivity for the hydrogenation of SUC to GBL.The catalysts were characterized by TGA, FTIR, XPS, ICP-AES, BET, H2 chemisorption, TEM, AC-HAADF-STEM and XRD techniques. The characterization results reveal that the incorporation of 3-(2-aminoethylamino)-propyltrimethoxysilane (AAPTS) in the preparation process of 1.0%Pd/SiO2-NH2 catalyst can effectively improve the dispersion of palladium nanoclusters on the support. The synthesized catalyst exhibits high catalytic activity for SUC hydrogenation with 100%conversion and 94% selectivity towards GBL using 1,4-dioxane as solvent at 240℃ and 60 bar H2 for 4 h. The catalyst is also robust and readily reusable without loss of its catalytic activity. As for Pd/TiO2 catalysts,1.0%Pd/TiO2 (400) catalyst shows 90% SUC conversion and 94%selectivity to GBL at 200℃,100 bar H2 for 8 h using green solvent—water. The effect of palladium catalysts on hydrogenation of SUC displays that catalysts with the most active sites exhibit the best performances. As for Pd/SiO2-NH2 catalysts, the reaction process for hydrogenation of SUC to GBL can be conjectured through the conversion and selectivity versus time changes. Firstly, SUC is hydrogenated to 4-hydroxybutyric acid (GHB) and then GHB is dehydrated to the target product GBL.