Microfluidic synthesis enables highly dispersed Ru/ZrPO4 catalyst for hydrodeoxygenation of lignin-derived phenolic compounds

To address the demand for efficient hydrodeoxygenation (HDO) of lignin-derived phenolic compounds into high-value hydrocarbon fuels, this study designed and synthesized highly dispersed Ru/ZrPO4 catalysts by employing a novel microfluidic technology coupled with ethylene glycol thermal reduction. The traditional impregnation (Ru/ZrPO4-IMP) and the hydrothermal method (Ru/ZrPO4-HYD) were also conducted to compare with the microfluidic method (Ru/ZrPO4-MIC). Comprehensive characterizations via XRD, TEM, XPS, H2-TPD and NH3-TPD reveal that Ru/ZrPO4-MIC presents superior properties of small average Ru particle size (3.03 nm), excellent metal dispersion, outstanding hydrogen dissociation capability and suitable acid strength, which improve the HDO performance significantly. Under mild reaction condition (240 °C, 1 MPa H2), the Ru/ZrPO4-MIC achieves complete conversion of guaiacol and 97.9% selectivity toward cyclohexane, significantly outperforming the Ru/ZrPO4-IMP (47.4%) and Ru/ZrPO4-HYD (79.7%) catalysts, as well as most of the reported catalysts. Comparative studies confirm that the microfluidic approach effectively prevents metal agglomeration and enhances metal dispersion. Ru/ZrPO4-MIC catalyst also presents a high stability after 5 recycles, with little catalytic activity loss. Moreover, in the HDO upgrading of lignin oil, hydrocarbon content increases from 10.5% to 91.8%. This novel microfluidic method is also suitable for the preparation of other highly dispersed noble metal-based catalysts, which enables to achieve high catalytic activity under the low metal loading.