Efficient phenol-to-cyclohexanone hydrogenation enabled by hydrogen spillover in sub-nanometric Pd-polyoxovanadomolybdate catalysts

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.