Highly dispersed ultra-small Pd nanoparticles on gadolinium hydroxide nanorods for efficient hydrogenation reactions.

Heterogeneous catalytic hydrogenation reactions are of great importance to the petrochemical industry and fine chemical synthesis. Herein, we present the first example of gadolinium hydroxide (Gd(OH)) nanorods as a support for loading ultra-small Pd nanoparticles for hydrogenation reactions. Gd(OH) possesses a large number of hydroxyl groups on the surface, which act as an ideal support for good dispersion of Pd nanoparticles. Gd(OH) nanorods are prepared by hydrothermal treatment, and Pd/Gd(OH) catalyst with a low loading of 0.95 wt% Pd is obtained by photochemical deposition. The catalytic hydrogenation of p-nitrophenol (4-NP) to p-aminophenol (4-AP) and styrene to ethylbenzene is performed as a model reaction. The obtained Pd/Gd(OH) catalyst displays excellent activity as compared to other reported heterogeneous catalysts. The rate constant of 4-NP reduction is measured to be 0.047 s and the Pd/Gd(OH) nanocatalyst shows no marked loss of activity even after 10 consecutive cycles. Additionally, the hydrogenation of styrene to ethylbenzene over Pd/Gd(OH) nanorods exhibits a turnover frequency (TOF) as high as 6159 h with 100% selectivity. Moreover, the catalyst can be recovered by centrifugation and recycled for up to 5 consecutive cycles without obvious loss of activity. Our results indicate that Gd(OH) nanorods act as a promoter to enhance the catalytic activity by providing a synergistic effect from the strong metal support interaction and the large surface area for high dispersion of small sized Pd nanoparticles enriched with hydroxyl groups on the surface. The high performance of Pd/Gd(OH) in heterogeneous catalysis offers a new, efficient and facile strategy to explore other metal hydroxides or oxides as supports for organic transformations.