TY - JOUR
T1 - Oxygen adsorption and water formation on Co(0001)
AU - Kizilkaya, A.C.
AU - Niemantsverdriet, J.W.
AU - Weststrate, C.J.
PY - 2016/3/10
Y1 - 2016/3/10
N2 - Oxygen adsorption and removal on flat and defective Co(0001) surfaces have been investigated experimentally using scanning tunneling microscopy, temperature-programmed and isothermal reduction, synchrotron X-ray photoemission spectroscopy, and work function measurements under ultrahigh vacuum conditions and H2/CO pressures in the 10-5 mbar regime. Exposure of the Co(0001) to O2(g) at 250 K leads to the formation of p(2 × 2) islands with a local coverage of 0.25 ML. Oxygen adsorption continues beyond 0.25 ML, reaching a saturation point of ∼0.39 ML Oad, without forming cobalt oxide. Chemisorbed oxygen adlayers can be reduced on both flat and defective Co(0001) surfaces by heating in the presence of ∼2.3 × 10-5 mbar H2(g). The onset of the oxygen removal as water during temperature-programmed reduction experiments (1 K s-1) is at around 450 K on flat Co(0001) and 550 K on defective Co(0001). By evaluation of isothermal reduction experiments using a kinetic model, the activation energy for water formation is found to be ∼129 ± 7 kJ/mol for the flat Co(0001) and ∼136 ± 7 kJ/mol for the defective Co(0001). Adsorbed oxygen cannot be reduced by CO(g) on flat and defective Co(0001) using CO pressures up to 1 × 10-5 mbar and temperatures up to 630 K.
AB - Oxygen adsorption and removal on flat and defective Co(0001) surfaces have been investigated experimentally using scanning tunneling microscopy, temperature-programmed and isothermal reduction, synchrotron X-ray photoemission spectroscopy, and work function measurements under ultrahigh vacuum conditions and H2/CO pressures in the 10-5 mbar regime. Exposure of the Co(0001) to O2(g) at 250 K leads to the formation of p(2 × 2) islands with a local coverage of 0.25 ML. Oxygen adsorption continues beyond 0.25 ML, reaching a saturation point of ∼0.39 ML Oad, without forming cobalt oxide. Chemisorbed oxygen adlayers can be reduced on both flat and defective Co(0001) surfaces by heating in the presence of ∼2.3 × 10-5 mbar H2(g). The onset of the oxygen removal as water during temperature-programmed reduction experiments (1 K s-1) is at around 450 K on flat Co(0001) and 550 K on defective Co(0001). By evaluation of isothermal reduction experiments using a kinetic model, the activation energy for water formation is found to be ∼129 ± 7 kJ/mol for the flat Co(0001) and ∼136 ± 7 kJ/mol for the defective Co(0001). Adsorbed oxygen cannot be reduced by CO(g) on flat and defective Co(0001) using CO pressures up to 1 × 10-5 mbar and temperatures up to 630 K.
UR - http://www.scopus.com/inward/record.url?scp=84960878238&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.5b08959
DO - 10.1021/acs.jpcc.5b08959
M3 - Article
AN - SCOPUS:84960878238
SN - 1932-7447
VL - 120
SP - 4833
EP - 4842
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 9
ER -