An Atomically Precise Ru₁Au₆(TBBT)₆(PPh₃)₆ Cluster Catalyst for Ammonia Production

Only one active site in a catalyst is not able to handle a deal of multitasking at once to facilitate distinct elementary steps in a catalytic cycle. To overcome this, a multi-functional system is required by two or more functional units combined in one catalyst, with each unit playing a complementary role. Here we find that the Au site of Au(TBBT)PPh₃ (TBBT = 4-tert-butylbenzenethiol) complex not only activates water but also reduces nitrate to ammonia, resulting in a low efficiency for the electrocatalytic reduction of nitrate. To decouple the responsibility of the Au site, we synthesize a Ru₁Au₆(TBBT)₆(PPh₃)₆ cluster consisted of one Ru atom and six Au(TBBT)PPh₃ complexes bridged by the S atoms, in which the water dissociation is mostly undertaken on the Ru site for the steady supply of proton, while the nitrate is sequentially reduced on the Au sites. More notably, the hopping of proton from Ru to Au is readily proceeded over the S bridge, giving rise to positively cooperative couple of one Ru site and six Au sites among this cluster, and thereby 19-fold efficiency increase is observed in comparison to this complex catalyst.