Polyoxometalate (POM)-mediated cluster catalysis has emerged as a promising strategy for the development of efficient and selective catalysts because of its unique advantages in activity modulation, interface engineering, and electron/proton transfer. In this study, a series of sub-nanowire hybrid catalysts (denoted as Pd-PMo_12−xV_x, x = 0–3) is successfully constructed via a self-assembly strategy involving Keggin-type POMs and Pd⁰ clusters. Among them, Pd-PMo₁₀V₂ exhibits excellent catalytic performance for the selective hydrogenation of phenol to cyclohexanone, achieving 99.9% phenol conversion and 95.4% product selectivity. Experimental results demonstrate that POMs not only effectively stabilize sub-nano Pd⁰ clusters but also modulate their electronic structures, thereby enhancing the catalytic activity. Compared with tungsten-based POMs, molybdenum-based analogs exhibit stronger reducibility and superior electron/proton acceptance capabilities, which provide more efficient active hydrogen transfer channels for multi-hydrogenation processes. Moreover, increasing the reaction temperature can help overcome the energy barrier associated with the electron-coupled proton transfer process, thereby enabling the full utilization of redox active sites within POMs. This work provides a novel design strategy and mechanistic insight for the development of highly active and selective noble-metal cluster catalysts.

Clusters exhibit unique activity and selectivity in catalysis. However, research on the interactions between clusters and their synergistic catalysis is still in its infancy. Herein, ultrafine sub-nanowires composed of Pd⁰ sub-nanoclusters and polyoxometalates (POMs) stacked by cluster–cluster are successfully constructed (abbreviated as Pd-POMs). Notably, Pd-PW₁₂ exhibits exceptional activity (99%) and selectivity (99%) for the hydrogenation of C=C bonds in 4-vinylbenzaldehyde, significantly outperforming other supported Pd-based catalysts. Density functional theory (DFT) calculation results indicate that POMs can stabilize and adjust the electronic structure of Pd clusters, promoting the specific adsorption and reducing hydrogenation energy barriers of C=C bonds. Moreover, the electron–coupled proton (e⁻/H⁺) transfer process at the interface can be regulated by altering the redox properties of POMs, achieving extra regulations of the catalytic activity. This work reveals the synergistic optimization effects of POMs on the activity and selectivity of Pd clusters, providing new insights into the rational design of highly efficient catalysts.