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Deactivation of the water–gas-shift activity of Pd/ceria by Mo

“…Consistent with this, CeO 2 single crystals, which by definition have been heated to high temperatures during their preparation, are difficult to reduce except by very harsh treatments such as ion sputtering [12,13]. (Notice that ordered ceria films grown stabilized-zirconia crystals are highly reducible and should not be considered in this category [14].) Deactivation of the oxygen storage capacity of ceria by high temperatures in automotive applications is well known, and it is necessary to stabilize the reducibility of ceria for that application by mixing it with zirconia [15].…”

The effect of oxide dopants in ceria on n-butane oxidation

“…The increased reducibility of ceria-zirconia mixtures is usually explained by formation of solid solutions [18]. Again, others have reported that the most active form of ceria-zirconia is not a true solid solution [19]; and thick films of ceria on zirconia substrates were shown to be highly reducible, even when no solid solution had been formed [20][21][22]. Another possibility is that the facile reduction of ceria is associated with defect sites.…”

Ceria Surfaces and Films for Model Catalytic Studies Using Surface Analysis Techniques

“…Ce deposition and oxygen exposure (oxidation) may be performed simultaneously 16 or sequentially. 17 ' 18 Single crystal metals (Pt, 17 ' 19 Cu, 18 Pd, 20 Ni, 16 and Ru 16 ) and oxides, including yttrium-stabilized zirconia (YSZ), 21 and sapphire, 22 checked by "bulk" ex situ techniques such as XRD and SEM, but more typically in situ LEED patterns or ion scattering have been employed to show the symmetry of the surface, and XPS or AES is used to monitor the ceria growth. In most of the cases cited above, it seems that the ceria film is thought of as continuous and thick enough that it completely covered the substrate surface, as opposed to isolated islands of ceria with exposed substrate.…”

“…Ethylene adsorbs dissociatively on Rh, undergoing a sequence of dehydrogenations leading to hydrocarbon fragments (ref 97 and references therein). For Rh on ceria model catalysts the ethylene dehydrogenation and H 2 evolution mimic that of Rh single crystals, indicating these steps occur only on the metal particles with no influence or contribution from the ceria surface.…”

“…85 Similarly, since ethylene thus reduces the ceria, successive ethylene exposures and TPD experiments leads to an increasing CO desorption temperature. 22 ' 97 There is no C0 2 formation, since CO desorbs before further oxidation can occur. Ferrizz et al argue that the CO evolution is kinetically limited by the C + O reaction if the ceria is highly oxidized, but the rate limiting step shifts to oxygen transfer to the Rh if the ceria is highly reduced.…”