Size Dependent Catalytic Activity of Reusable Subnanometer Copper(0) Clusters

The catalytic reduction of methylene blue (MB) to leucomethylene blue (LMB) by hydrazine in the presence of size-selected copper clusters (CuCLs, CuN, N = number of atoms, 2 ≤ N ≤ 20) is demonstrated here. Only copper clusters smaller than ≈10–13 atoms enhance the rate of the reduction of MB. Cluster-mediated electron transfer through the cluster's lowest unoccupied molecular orbital (LUMO) frontier orbital is proposed as the main step for the catalysis. Catalyst recycling and stability were also studied demonstrating that they can be used as effective, stable, and reusable catalysts, which could be also employed in different types of redox reactions with important technological applications.