Support‐controlled Pd cluster catalysts for selective hydrogenation of α, β‐unsaturated aldehydes to saturated aldehydes

Selective hydrogenation of α, β‐unsaturated aldehydes remains challenging due to competitive CC and CO bond activation. We report an aerosol spray‐pyrolysis synthesis of Pd catalysts with tunable dispersions of nanoparticles, clusters, and single atoms, by varying the Ti/Ce ratio in supports. Pd clusters on Ti‐doped CeO 2 achieve 97.9% selectivity toward CC hydrogenation of cinnamaldehyde (CAL) to phenylpropanal (HCAL) under mild conditions (70°C, 1 MPa H 2 ), along with complete conversion within 0.5 h, outperforming nanoparticles (56.1%) and single‐atom dominant catalysts with a favored selectivity of acetalization. Synchrotron XAFS, AC‐STEM, and DFT reveal that clusters enable homolytic H 2 cleavage and strong CC adsorption (−1.39 eV), while single‐atom sites promote heterolytic splitting leading to acid‐catalyzed side reactions. The catalyst shows robust recyclability over 10 cycles, and the strategy is universal for acrolein and crotonaldehyde. This work establishes a structure‐selectivity framework and offers a potentially scalable catalyst design for sustainable biorefinery processes.