Abstract: Pd/UiO-66, Pd/UiO-66-NH2 and Pd/UiO-67-bpydc catalysts were prepared by impregnation method using a series of Zr-based MOFs materials with the same topological structure as supports. The primary focus wan to investigate the influence of different nitrogen-containing ligands in the supports on the size of Pd particles, the electron density, and the hydrogenation pathway of furfural. The characterization results of XPS, CO-FTIR, and TEM indicate that there are interactions of varying strengths between different N-containing ligands and Pd particles, this interaction not only regulate the size of Pd particles but also have a significant impact on the electron density of Pd. Catalytic reaction results show that different N-containing ligands resulted in significant differences in both the activity of the catalyst and the selectivity of the products, from the perspective of activity, an appropriate metal-support interaction between Pd and the different supports enhanced the activity of the Pd/Zr-MOFs catalysts, while excessively strong interactions suppressed catalytic activity. Regarding selectivity, the electron density of Pd is a key factor affecting the selectivity of furfural hydrogenation pathway. Specifically, the amino nitrogen in UiO-66-NH2 and the bipyridine nitrogen in UiO-67-bpydc not only promote the dispersion of Pd particles, but also facilitate the electron transfer between UiO-66-NH2 and UiO-67-bpydc and Pd particles. For the Pd/UiO-67-bpydc and Pd/UiO-66-NH2 catalysts with higher electron density, furfural preferentially undergoes hydrogenation through the aldehyde group (C=O ) in the side chain, for the Pd/UiO-66 catalyst with lower electron density, furfural preferentially undergoes hydrogenation through the furan ring C=C double bond.

Key words: Pd/Zr-MOF catalysts, Furfural hydrogenation, Reaction pathway, Pd electron density