CO and O-2 adsorption on alpha-Mo2C (0001)

CO and O-2 chemisorption on Mo- and C-terminated faces of alpha -Mo2C (0001 ) was investigated. CO adsorbs molecularly, and thermal desorption spectros copy (TDS) studies indicate one CO chemisorption state with an apparent fir st-order activation energy for desorption of 93 kJ mol(-1) at saturation co verage. O-2 adsorbs dissociatively, resulting in a(1 x 1)rectangular overla yer on the Mo-terminated surface. CO is the only thermal desorption product detected from an oxygen-saturated surface, yielding a low temperature deso rption-limited feature and a high temperature reaction-limited feature. How ever. the majority (similar to 85%) of the surface oxygen does not burn off as CO, but instead diffuses into the sample bulk. For the C-terminated sur face, the CO and O-2 saturation coverages are not significantly altered. Re lative surface coverages based on the total number of surface Mo atoms are 14% for CO and 50% for oxygen atoms. (C) 2000 Elsevier Science B.V. All rig hts reserved.