Tuning the Selectivity of Acetylene Polymerization Atom by Atom

The polymerization of acetylene was studied by thermal programmed reaction on nanoassembled model catalysts fabricated by soft landing of size-selected palladium Pd_n (1≤n≤30) clusters on well-characterized MgO(100) thin films. In a single-pass heating cycle experiment, benzene, butadiene, and butene were catalyzed with different selectivities as a function of cluster size: palladium atoms selectively produce benzene, and the highest selectivity for butadiene is observed for Pd₆, whereas Pd₂₀ reveals the highest selectivity for butene. These results provide an atom-by-atom observation of the selectivity of small palladium model catalysts, and extend toward small cluster sizes the study of Ormerod and Lambert on real palladium catalysts, where a structure sensitivity for the cyclotrimerization was observed.