Genesis of Bimetallic Pt-Cu Clusters in Reverse Micelles Investigated by in Situ X-ray Absorption Spectroscopy

摘要

The formation mechanism of platinum-copper(Pt-Cu)bimetallic clusters at the early stage within the water-in-oil microemulsion system of water/sodium bis(2-ethyl hexyl)sulfosuccinate-heptane is explored by in situ X-ray absorption spectroscopy.The reduction of platinum and copper ions and the formation of corresponding clusters are monitored as a function of the dosage of reducing agent,hydrazine(N_2H_4).Upon successive addition of the reducing agent,hydrazine(N_2H_4),five distinguishable steps are observed in the formation process of Pt-Cu clusters at the early stage.Both in situ X-ray absorption near-edge structure and extended X-ray absorption fine structure at the Pt L_(III)-edge suggest the Pt~(4+)- Pt~(2+)- Pt° reduction sequence,and analysis of the spectra recorded at the Cu K-edge confirms the Cu~(2+)->Cu~0 reduction sequence.A corresponding structural model is proposed for each step to provide detailed insight into the mechanism of nucleation and growth of Pt-Cu bimetallic clusters.