Paramagnetic CO species adsorbed on the surface of scandium, yttrium, and lanthanum oxides

Abstract

The interaction of CO molecules with the surface of Sc, Y, and La oxides leads to the formation of paramagnetic polyatomic surface compounds containing two equivalent carbon atoms and lattice cations; a structure for the adsorbed (CO)2.radical anions which explains their high thermal stability and reactivity has been suggested.The nature of intermediate surface compounds is important in elucidating the mechanism of catalytic reactions involving CO. A large number of variations of the forms of adsorbed CO have been found on oxide catalysts of a basic type. In addition to the usual carbonyl and carbonate-carboxylate structures, surface ionic compounds containing two and more adsorbate molecules have been formed. They were detected on Mg01J and rare earth oxides3.4 by optical and e.s.r. spectroscopy. With rare earth oxides (-20% of m ~n o l a y e r ) ~ the maximum chemisorption of CO as dimers (compared with that on monometallic oxides) was attained.3,4The aim of the present work was to establish the structure of the surface compounds which are formed during the interaction of CO with rare earth oxides by e.s.r. methods using W O and D20. The e.s.r. spectra were obtained on a Jeol JES-3BS-Q radiospectrometer in X and Q bands.The Sc, Y, and La oxides evacuated at 800-1100 K gave signals with g = 2.003 (Figure 1, signal A) when CO was admitted at 230-620 K. The spectra of radical A on scandium, yttrium, and lanthanum oxides possessed different

EPR Characterization and Reactivity of Surface-Localized Inorganic Radicals and Radical Ions

“…The reactions observed 120 can be described as follows: Some ethylenedione anions are stabilized at the surface, where they are observed by EPR, while others react with electrons to give the diamagnetic C 2 O 2 2ion, which, in turn, undergoes a series of condensation reactions, producing cyclic and linear oxycarbon dianions (C n O n 2-) which have been observed by vibrational spectroscopy. 123,124 Polymeric radical species derived from CO, and similar to those described here for MgO, have been reported on scandium, yttrium, and lanthanum oxides 125 and on zirconium dioxide. 126…”

Adsorption of carbon monoxide on a SmOx film

“…7 They have reported that CO chemisorbed reactively on a Sm 2 O 3 surface to form several types of species, which were also detected on other rare earth oxides. 8 On the other hand, under UHV conditions, no CO chemisorption was observed on rare earth oxide films 2 or single crystal surfaces of a rare earth oxide 3 at room temperature. The characteristic weak adsorption state of CO observed here on the SmO x surface was not stable at room temperature under UHV condition.…”