This study reports and compares the adsorption and dissociation of water on oxidized and reduced CeO 2 (100) and CeO 2 (111) thin films. Water adsorbs dissociatively on both surfaces. On fully oxidized CeO 2 (100) the resulting surface hydroxyls are relatively stable and recombine and desorb as water over a range from 200 to 600 K. The hydroxyls are much less stable on oxidized CeO 2 (111), recombining and desorbing between 200 and 300 K. Water produces 30% more hydroxyls on reduced CeO 1.7 (100) than on oxidized CeO 2 (100). The hydroxyl concentration increases by 160% on reduced CeO 1.7 (111) compared to oxidized CeO 2 (111). On reduced CeO 1.7 (100) most of the hydroxyls still recombine and desorb as water between 200 and 750 K. Most of the hydroxyls on reduced CeO 1.7 (111) react to produce H 2 at 560 K, leaving O on the surface. A relatively small amount of H 2 is produced from reduced CeO 1.7 (100) between 450 and 730 K. The differences in the adsorption and reaction of water on CeO X (100) and CeO X (111) are attributed to different adsorption sites on the two surfaces. The adsorption site on CeO 2 (100) is a bridging site between two Ce cations. This adsorption site does not change when the ceria is reduced. The adsorption site on CeO 2 ( 111) is atop a single Ce cation, and the proton is transferred to a surface O in a site between three Ce cations. When the CeO X (111) is reduced, vacancy sites are produced which allows the water to adsorb and dissociate on the 3-fold Ce cation sites. Recently, Molinari et al. 9 calculated that dissociation is favored

X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO2(111) surfaces. Upon adsorption on CeO2(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500–800 K) leads to partial reduction of the ceria substrate with the formation of Ni2+ species that exists as NiO and/or Ce1−xNixO2−y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO2(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce+3 cations, CO dissociates on the surface at 300 K forming NiCx compounds that may be involved in the formation of CH4 at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO2(111) surfaces are able to catalyze the production of methane from CO and H2, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO2(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water–gas shift reaction

This study reports the interaction of methanol, ethanol, 1-propanol, and 2-propanol with well-ordered CeO2(111) thin film surfaces. All of the alcohols adsorb at low temperature by forming alkoxy and hydroxyl species on the surface. On fully oxidized CeO2(111), recombination occurs between some of the alkoxys and hydroxyls, resulting in alcohol desorption near 220 K. At the same temperature, some of the surface hydroxyls disproportionate to produce water and the loss of lattice O. The remaining alkoxys react above 550 K. The primary alcohols favor dehydrogenation products (aldehydes). There is a net loss of O from the system, resulting in a reduction of the ceria. The secondary alcohol, 2-propanol, undergoes primarily dehydration, producing propene with no net change in the cerium oxidation state. Reduced CeO X (111) competes with the gaseous products for available O. Little or no water is produced. The reaction selectivity for the C2 and C3 alcohols shifts toward favoring dehydration products. The loss of O from the alcohols leads to oxidation of the reduced ceria. Compared with the oxidized surface, the alkene desorption shifts to lower temperature, whereas the aldehyde desorption shifts to higher temperature. This indicates that, on the reduced surface, it is easier to break the C−O bond but more difficult to break the O-substrate bond.

This study reports the interaction of acetaldehyde with well-ordered CeO X (111) thin film surfaces. The fully oxidized CeO2(111) surface shows a weak interaction with acetaldehyde with the sole desorption product (TPD) being the parent molecule at 210 K. The chemisorbed molecule binds to the surface as the η1-acetaldehyde species rather than through a bridge-bonded dioxy configuration. Acetaldehyde chemisorbs strongly on reduced CeO2−X (111) with nonrecombinative and recombinative acetaldehyde desorbing at 405 and 550−600 K, respectively. Deoxygenation and dehydration also occur, producing ethylene and acetylene at 580 and 620 K, respectively. Acetaldehyde initially adsorbs in the η1 configuration and then converts to a carbanion species with both CC and CO bond character above 300 K.