Jm. Guevremont et al., EFFECTS OF SURFACE IMPERFECTIONS ON THE BINDING OF CH3OH AND H2O ON FES2(100) - USING ADSORBED XE AS A PROBE OF MINERAL SURFACE-STRUCTURE, Surface science, 391(1-3), 1997, pp. 109-124
Studies are presented that investigate the adsorption and binding of C
H3OH and H2O on the atomically clean (100) crystallographic plane of p
yrite, FeS2. Temperature programmed desorption suggests that both reac
tants adsorb molecularly at 90 K and desorb thermally between 170 and
400 K depending on the surface coverage. Photoemission of adsorbed xen
on (PAX) suggests that the surface of pyrite is heterogeneous and cont
ains a significant fraction of defect sites that are believed to be, a
t least in part, anion vacancy or sulfur-deficient sites. An upper lim
it of 0.2 is proposed for the fraction of surface sites that are defec
ts on FeS2(100). PAX indicates that these defect sites at low adsorbat
e coverage serve as the exclusive binding sites for H2O and CH3OH adso
rbate, We speculate, on the basis of our ability to interpret PAX data
for pyrite, that PAX may be of use for understanding the effect of sh
ort range order on adsorbate binding on other complex mineral surfaces
. On the basis of high resolution electron energy loss spectroscopy, i
t is found that some dissociation of the adsorbate occurs on the pyrit
e. Vibrational data obtained with this technique suggests that Fe-O sp
ecies result from the adsorbate decomposition, After saturation of the
defect sites, further molecular adsorption is accommodated on the les
s reactive surface that we postulate is largely disulfide, the charact
eristic structural group of pyrite. (C) 1997 Elsevier Science B.V.