Vi. Bukhtiyarov et al., X-ray absorption and photoemission studies of the active oxygen for ethylene epoxidation over silver, CATAL LETT, 74(3-4), 2001, pp. 121-125
Activation of clean polycrystalline silver by a C2H4 + O-2 reaction mixture
has been studied by XANES, XPS, and UPS. In situ monitoring of the O K-edg
e XAS spectrum of the pre-treated silver surface revealed a broad signal at
10-20 eV above the threshold. The comparison of the X-ray absorption spect
ra with O Is and valence band photoemission data allowed us to attribute th
is XAS signal to "electrophilic" oxygen (Eb(O Is) = 530.4 eV) which is know
n to be active in ethylene epoxidation. The complete absence of XAS feature
s in the photon energy range typical for pi* and sigma* transitions of mole
cular oxygen (530-535 eV) indicates both the atomic origin of the electroph
ilic oxygen and the absence of molecular species on the catalyst surface un
der the present reaction conditions.