Tuning the microenvironment of nanoreactors transforms ruthenium nanoparticles (NPs) from an inactive to active state for benzoic acid hydrogenation in organic solvent. In their Communication on https://doi.org/10.1002/anie.201908602page 14483 ff., L. Yu, J. Liu, Q. Yang, et al. show that encapsulation of metal NPs in nanoreactors with a precise microenvironment, mimicking the process of natural catalysts, is an efficient strategy to improve catalytic performance.