Oxidative stress and inflammation are at the root of a multitude of diseases. Treatment of these conditions is often necessary but current standard therapies to fight excessive reactive oxygen species (ROS) and inflammation are often ineffective or complicated by substantial safety concerns. Nanozymes are emerging nanomaterials with intrinsic enzyme‐like properties that hold great promise for effective cancer treatment, bacterial elimination, and anti‐inflammatory/anti‐oxidant therapy. While there is rapid progress in tailoring their catalytic activities as evidenced by the recent integration of single‐atom catalysts (SACs) to create next‐generation nanozymes with superior activity, selectivity, and stability, a better understanding and tuning of their safety profile is imperative for successful clinical translation. This review outlines the current applied safety assessment approaches and provides a comprehensive summary of the safety knowledge of therapeutic nanozymes. Overall, nanozymes so far show good in vitro and in vivo biocompatibility despite considerable differences in their composition and enzymatic activities. However, current safety investigations mostly cover a limited set of basic toxicological endpoints, which do not allow for a thorough and deep assessment. Ultimately, remaining research gaps that should be carefully addressed in future studies are highlighted, to optimize the safety profile of therapeutic nanozymes early in their pre‐clinical development.

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)₃) nanorods as a support for loading ultra-small Pd nanoparticles for hydrogenation reactions. Gd(OH)₃ possesses a large number of hydroxyl groups on the surface, which act as an ideal support for good dispersion of Pd nanoparticles. Gd(OH)₃ nanorods are prepared by hydrothermal treatment, and Pd/Gd(OH)₃ 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)₃ 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⁻¹ and the Pd/Gd(OH)₃ nanocatalyst shows no marked loss of activity even after 10 consecutive cycles. Additionally, the hydrogenation of styrene to ethylbenzene over Pd/Gd(OH)₃ nanorods exhibits a turnover frequency (TOF) as high as 6159 h⁻¹ 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)₃ 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)₃ in heterogeneous catalysis offers a new, efficient and facile strategy to explore other metal hydroxides or oxides as supports for organic transformations.

Oxygen-deficient Pd/Pr ₆ O ₁₁ nanocatalysts with strong metal-support interaction exhibit highly efficient styrene and 4-NP hydrogenation reactions performance.