Binuclear gold phosphine complexes as single-source precursors for CO oxidation catalysts: insights into the formation of surface-stabilized Au particles

We herein present the application of atomically precise binuclear gold phosphine complexes as precursors for supported Au catalysts tested in CO oxidation. Using a variety of complementary analytical techniques, including transmission electron microscopy imaging, in-situ and operando X-ray absorption spectroscopy, and diffuse reflectance infrared Fourier transformed spectroscopy, we discovered that minor changes in the ligand arrangement of molecular Au phosphine complexes result in significantly different activation behaviors of alumina-supported Au catalysts under reaction conditions. When using [Au2(μ2-POP)2]OTf2 (POP = tetraphenylphosphoxane) as a single-source precursor, we obtained an active supported Au oxidation catalyst in the second light-off, outperforming both a commercial Au/TiO2 and a P-free Au/Al2O3 reference catalyst. Conversely, using [Au2(μ2-dppe)2]OTf2 (dppe = diphenylphosphinoethane) on alumina led to a significant decrease in CO oxidation activity. This difference is attributed to the formation of a P-containing binding pocket in the case of [Au2(μ2-POP)2]OTf2/Al2O3, which not only enhances the thermal stability of the Au particles but also affects their electronic properties through charge transfer processes from Au to P. In contrast, the molecular precursor of [Au2(μ2-dppe)2]OTf2/Al2O3 is too stable and produces gold nanoparticles with blocked active sites. This work provides detailed insights into the ligand decomposition of molecular gold phosphine complexes under reaction conditions and demonstrates the delicate balance between the stabilization of Au particles, clusters and complexes using ligands and the blocking of active surface sites by strongly coordinating molecules. This knowledge will pave the way for the targeted use of molecular transition metal complexes as precursors in synthesizing surface-stabilized nanoparticles.