X-ray photoelectron spectra (XPS) were used to probe the electronic properties of the PtnGe/alumina catalysts and measure the Ge:Pt stoichiometry, which was found to be 1.07:4, i.e., roughly one Ge atom was deposited per Pt4 cluster. In addition, there was some non-specific Ge deposition on the alumina support, but as shown below and in the supporting information, this alumina-bound Ge is not catalytically active itself, and has little effect on the catalytic properties of Ptn clusters deposited on a Ge-treated alumina support. As shown in Figure , the Ge 2p3/2 peak for Pt4Ge is shifted slightly to lower binding energy compared to that for Ge bound directly to the alumina support, reflecting the difference in electronic environment.