CO Adsorption on FeO x Nanoclusters Supported on HOPG—Effect of Oxide Formation on Catalytic Activity

Abstract

CO adsorption on FeO x clusters has been characterized by thermal desorption spectroscopy (TDS) and molecular beam scattering. Iron was vapor deposited and oxidized by annealing in O 2 . The TDS curves consist initially of two peaks indicating formation of c-Fe 2 O 3 / Fe 3 O 4 . Increasing the O 2 exposure results in one TDS peak and the dominance of a-Fe 2 O 3 .

Adsorption dynamics and kinetics of CO2 on Fe/FeOx nanoclusters supported on HOPG

“…2(B)) may be related to different crystal planes present in the larger Fe clusters. Alternatively, and in analogy to the results obtained for CO adsorption on iron-oxide clusters, [41] the α 1 /α 2 -peak also may be assigned to adsorption of CO 2 (Fig. 1(B)) is assigned to carbonate formation, probably involving surface oxygen as suggested in prior studies [23] on iron oxides.…”

“…In addition, the averaged stoichiometry (x in FeO x ) has been estimated by measuring oxygen and iron AES line intensities (x = AES-O 506 /AES-Fe 703 ) and is included in the figure captions. [41] Accordingly, the averaged stoichiometry for most of the data presented here amounts to 0.57 ± 0.07. Thus, it appears that even under UHV conditions, mostly iron-oxide clusters are formed.…”

“…Thus, it appears that even under UHV conditions, mostly iron-oxide clusters are formed. According to the data [41] obtained with CO and prior studies on single crystals, mixed Fe 2 O 3 /Fe 3 O 4 oxides and a small amount of metallic Fe clusters are formed.…”

“…The equivalent Fe coverage has been estimated from AES and CO-TDS measurements; 1 ML corresponds to an exposure, χ Fe , where a transition from two-dimensional to three-dimensional cluster growth was indicated by AES/TDS data. [41] The impact energy, E i , of the CO 2 molecules could be varied within (0.12-1.0) eV by seeding 3% CO 2 in He, combined with a variation of the nozzle temperature. [51] The adsorption isotherms (King and Wells curves [52] ) are smoothed while conserving the shape of the curves.…”

“…The deposition of Fe has been characterized in a prior study [41] by means of TDS and AES. In doing so, the Fe coverage, Fe , could be estimated and is given in the figures.…”