drawbacks, including the low boiling point and high toxicity of methanol, together with severe catalyst poisoning during long-term operation. [3,4] To address these issues, one can switch to alcohols with high molecular weights, such as ethylene glycol (EG) and glycerol that feature high boiling points and low toxicity. [5] With regard to the catalyst, an effective strategy is to incorporate Ru into the conventional Pd catalysts for the formation of a Pd-Ru alloy. The alloy-based catalysts are capable of not only enhancing the activity by modulating the electronic structure but also significantly improving the durability owing to the increased resistance to CO poisoning. [6][7][8] Additionally, compared with other precious metals such as Pt and Rh, Ru has a relatively high abundance in the Earth's crust and its current price is about three times lower than those of Pt and Rh, making it promising for the large-scale use in commercial applications. [9] However, Pd and Ru take completely different crystal structures in the bulk, face-centered cubic (fcc) for Pd versus hexagonal close-packed (hcp) for Ru, and their reduction potentials also show significant difference (Pd 2+ /Pd: 0.95 V vs the standard hydrogen electrode (SHE); Ru 3+ /Ru: 0.39 V vs SHE), making it challenging to synthesize Pd-Ru alloy catalysts with controllable compositions and structures. Thus far, the Pd-Ru catalysts reported in literature were mainly based on irregular nanoparticles, and nanoflowers or nanobranches featuring a low content of Ru. [10][11][12][13][14][15][16][17][18] As an alternative to the conventional catalysts based upon solid nanoparticles, nanocages have recently emerged as an intriguing class of catalysts for various reactions. [19][20][21][22][23][24][25] The characteristic hollow structure, ultrathin and porous walls of nanocages are advantageous in maximizing the atom utilization efficiency while the well-controlled surface structures could be leveraged to optimize the active sites. [26,27] One effective route to the synthesis of nanocages is based upon galvanic replacement, which involves the spontaneous reduction of metal ions at the expense of oxidation of a sacrificial template. [28] Moreover, galvanic replacement can be completed within a short period, making it attractive for practical applications. [29][30][31] Regarding the synthesis of Pd-Ru nanocages, despite the well-established protocols for the production of Pd nanocrystals with diverse This article reports a facile method for the synthesis of Pd-Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with Iions. The as-synthesized nanocages feature a hollow interior, ultrathin wall of ≈2.5 nm in thickness, and a cubic shape. Our quantitative study suggests that the reduction rate of the Ru(III) precursor can be substantially accelerated upon the introduction of Iions and then retarded as the ratio of I -/Ru 3+ is increased. The Pd-Ru nanocages take an alloy structure, with the Ru atoms in the nano cages cr...