Highly Selective Hydrogenation of Phenol to Cyclohexanone Using WO3 Supported Tiny Pd Clusters Catalysts

Abstract Cyclohexanone is a crucial intermediate for producing nylon and other industrial products. However, the direct hydrogenation of phenol for synthesizing cyclohexanone easily generates cyclohexanol and thus reduce the yield. In this work, the Pd/WO 3 catalysts with different Pd contents (Pd/WO 3 -1–0.21 wt%, Pd/WO 3 -2–0.69 wt%, Pd/WO 3 -3–2.20 wt%) are prepared via using sodium borohydride liquid phase reduction, which have good catalytic performance for phenol selective hydrogenation. The Pd/WO 3 -2 catalyst can achieve 92.9% conversion, 84.4% selectivity and high TOF (turnover frequency) of 349.1 h −1 under the reaction conditions (120 °C, 2 h, 3.0 MPa H 2 ). The nanostructures of the catalysts are extensively characterized by XRD, XPS, SEM, TEM, HRTEM, STEM and STEM-EDS elemental mapping and line-scanning. It is found that the Pd/WO 3 -2 catalyst has a high Pd dispersion and quite tiny Pd clusters. Alternatively, the stability experiment of Pd/WO 3 -2 indicates that the conversion decreases from 92.9% to 87.5% and the selectivity to cyclohexanone does not change significantly (84%) after it is recycled for five times. Graphic Abstract