Atom-precise silver-palladium bimetallic clusters on carbon supports as selective hydrogenation catalysts

Bimetallic atom-precise Ag24Pd1(SR)(18)(2-) clusters on carbon supports were prepared, characterized, and evaluated as heterogeneous catalysts for hydrogenation reactions. Element-specific X-ray spectroscopy data suggests that the single Pd atom resides in the thiolate environment in the cluster structure and thus is accessible for hydrogenation catalysis. XAS data indicated that bimetallic Ag24Pd1(SR)(18)(2-) clusters exhibit better thermal stability than homonuclear Ag-25(SR)(18)(-) clusters on carbon supports, and significant Pd-S interactions still exist after calcination at 250 & DEG;C. Both Pd K-edge and that Pd L-3-edge measurements indicated that after calcination at 450 & DEG;C the resulting Ag24Pd1 clusters consist mostly of zerovalent Ag and Pd, with a trace amount of PdOx species. Carbon-supported Ag24Pd1(SR)(18)(2-) bimetallic cluster catalysts showed improved catalytic activity compared to homonuclear Ag-25(SR)(18)(-) cluster catalysts in the hydrogenation reactions of 2-methyl-butyn-1-ol (MBY) and 3-hexyn-1-ol (HY) as model alkynol substrates. The Ag24Pd1(SR)(18)(2-) cluster catalysts also showed excellent chemoselectivity for selective hydrogenations to alkenols and stereoselectivity towards the Z-isomer of 3-hexen-1-ol (Z-HE). The presence of residual thiolate ligands on activated Ag24Pd1 clusters led to higher selectivity towards semi-hydrogenation products.

Automated summary

Bimetallic atom-precise Ag24Pd1(SR)(18)(2-) clusters on carbon supports were synthesized and used as heterogeneous catalysts for hydrogenation reactions. The single Pd atom in the cluster structure was found to be accessible for the hydrogenation catalysis. The bimetallic Ag24Pd1(SR)(18)(2-) clusters exhibited better thermal stability and higher catalytic activity than homonuclear Ag-25(SR)(18)(-) clusters on carbon supports.