Photo/Thermal Sequential Catalytic Production of Bio-ε-Caprolactam from Succinic Acids over a Ru/TiO₂ Catalyst

Developing an efficient biomass-based route for ε-caprolactam synthesis under mild conditions with a single robust catalyst is highly sought after but remains challenging. This study presents an efficient strategy for synthesizing ε-caprolactam from succinic acid derivatives through a two-stage process integrating photocatalytic decarboxylative alkylation and thermocatalytic reductive cyclization. By incorporating Ru particles on TiO2, the photocatalytic decarboxylation of monoethyl succinate and subsequent Giese addition into acrylonitrile were achieved (ambient pressure and temperature, 365 nm irradiation), followed by the thermocatalytic hydrogenation of ethyl 5-cyanopentanoate (2 MPa H2, 180 °C) to form ε-caprolactam, with yields of 81 and 70%, respectively. This innovative two-in-one catalytic system eliminates the need for additional catalysts and offers reusability, reducing costs and enhancing practical applicability. The mechanism was comprehensively studied, providing insights into extending this approach to other reactions. Compared to traditional routes, this method addresses key challenges, such as environmental impact, poor selectivity, and harsh conditions, demonstrating significant potential for ε-caprolactam production and broader chemical applications.