“…Thus far, characterization of the low-loading regime has been pursued with a variety of techniques, all of which probe relatively large surface areas, yielding an average signal. [3,5,8,9] It has been inferred that "surface chromate species", as opposed to fragments of stoichiometric oxides, are responsible for catalysis. Efforts to determine the oxidation state of Cr in catalytically active species have yielded conflicting results, but a consensus has emerged that Cr 6+ is present.…”