Selective Hydrogenation of Quercetin to Dihydroquercetin Using a Carbon Nanotube-Supported Non-Noble Nickel Catalyst

Dihydroquercetin (DHQ) is a flavonoid compound with notable pharmacological activities. Developing a green and efficient synthesis route for its sustainable production remains a considerable challenge. This study proposed a semisynthetic strategy based on a non-noble nickel catalyst for the selective catalytic hydrogenation of quercetin to produce DHQ. Under the conditions of 200 °C and 7 MPa H2 for 2 h, the Ni/CNT catalyst achieved a DHQ yield of 32.3% from quercetin, which is markedly higher than the commercial Pd/C catalyst (13.2%). This can be attributed to the synergistic effect between its unique structural characteristics and the underlying electronic effects. Based on the dual descriptor theory for predicting reaction sites and comparative experiments with different supports, this study clarified the inherent selectivity challenges in the hydrogenation of quercetin to DHQ and highlighted the key role of the unique tubular curved structure of carbon nanotubes. Furthermore, kinetic analysis in this study determined that the activation energy for the selective hydrogenation of quercetin to DHQ catalyzed by Ni/CNT is 76.15 kJ/mol. Further analysis revealed that the activation energy for the DHQ formation step is higher than that for its subsequent consumption step (Ea1 > Ea2), and the consumption rate constant is greater than the formation rate constant (k2 > k1). These results indicate that DHQ, as an intermediate, is difficult to accumulate, highlighting the necessity of precise control over reaction conditions to improve its yield, thereby providing a basis for the development of a green and efficient DHQ synthesis process.