Heterogeneous
single-metal-site catalysts (HSMSCs) have attracted
considerable interest, but most studies have focused on the metal
atoms in the active site while ignoring the key role of ligands. The
unique coordination environment of a single-site catalyst is crucial
for realizing its potential. Constructing this kind of catalyst via a feasible and practical fabrication method is challenging.
Herein, a single-site Pd catalyst with iodide ligands supported on
activated carbon (Pd1/AC) was successfully fabricated by
atomic dispersion of large Pd nanoparticles (NPs). Intermediate I•
radicals were detected during the atomic dispersion process of Pd
NPs by in situ imaging photoelectron photoion coincidence
spectroscopy (in situ iPEPICO) with vacuum ultraviolet
synchrotron radiation. The molecular structure of single-site Pd was
established as [Pd(CO)I4(OAC)]2– through combined characterization. Alkyne dialkoxycarbonylation
with high selectivity toward 1,4-dicarboxylic acid esters (>94%)
and
high acetylene conversion (>99%) was achieved. A sulfonic promoter
on the Pd1/AC catalyst for alkyne dialkoxycarbonylation
was avoided because of the iodide ligand. Good durability and a broad
substrate scope were successfully achieved.
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