Engineering Ru-based catalysts via cooperating with alkaline metals for partial hydrogenolysis of dimethyl oxalate

Partial hydrogenolysis of dimethyl oxalate (DMO) to methyl glycolate (MG) is a central step in biodegradable polyglycolic acid (PGA) production. However, it remains a great challenge for efficient and selective DMO hydrogenolysis under mild temperature (<100°C). In this work, we demonstrate an outstanding DMO hydrogenolysis by employing alkaline (Na, K) metal-doped Ru catalysts. Na presents a stronger promotional effect than K. The highest yield of MG is achieved at 90.2% at 85°C in 15 h of reaction on 3Ru-0.4Na/SiO₂ and the catalyst can be directly reused more than 10 times without any additional regeneration. The doping of Na effectively enables smaller Ru nanoparticle size, larger capacity of H₂ adsorption via a hydrogen pool (includes surface hydride, i.e., Na-H^δ−) on Ru–Na interface, stronger strength of DMO adsorption. It is further revealed that there is a linear relation between the content of surface Ru⁰ + Ru³⁺ + Ru^δ− and MG yield. Finally, an optimal ratio of Ru³⁺ + Ru^δ−/Ru⁰ of 1.26 is achieved.