The interaction of KOH with clean and oxidized carbon surfaces

Abstract

The interaction of KOH with oxidized edge graphite and glassy carbon surfaces was studied with Auger electron spectroscopy (AES), ultraviolet photoemission spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). These results are compared to those from pure KOH deposited on the oxygen free basal and edge surfaces of graphite. Submonolayer concentrations of a potassium-oxygen surface species, which are stable to 800 °C under vacuum, are formed from KOH on preoxidized edge graphite and glassy carbon surfaces. Similar properties are found on glassy carbon surfaces after potassium-catalyzed gasification in CO 2. XPS from these surfaces show two O( ls) peak envelopes centered near 531 and 533 eV. The higher binding energy peak is characteristic of oxygen strongly bound to carbon. Heating to 950 °C results in the loss of potassium and the lower binding energy oxygen peak associated with potassium. The presence of an oxidized carbon surface enables development of stable potassium-oxygen surface species from KOH. Pure KOH interacts reversibly with the oxygen-free edge graphite surface and does not produce a form of potassium which is stable above 500 °C under vacuum. Our results show the presence of strongly bound potassium surface intermediates in inert environments. As a consequence, a catalytic cycle can be postulated which does not involve bulk-like K 2O or K 2CO 3.