Ceria-zirconia

K.B. Yi, Ceria-Zirconia oxide high temperature desulfurization sorbent, Ph.D. Thesis, Louisiana State University, 2004. 

Binet, C. and Daturi, M. (2001) Methanol as an IR probe to study the reduction process in ceria-zirconia mixed compounds, Catal. Today, 70, 155. 

We shall mainly consider, in the present chapter, non-precious transition metals, but the model can be extended to precious metals presenting an oxidation state higher than zero [10,11], such as Rhx+, Pdx+, Ptx+ and tix+. The model also applies to some oxides alone, such as ceria (Ce02) [19] or mixed oxides such as ceria-zirconia (CeZr02) able to present redox properties and oxygen vacancies during catalytic reactions. 

On ceria or ceria—zirconia, OHs species are generally associated to the formation of CeOOH groups with a correlative reduction of the surface [32,33],... 

Although the catalyst did not recover in the reformate stream, the authors did indicate that the carbonate species could be removed by air treatment at temperatures > 400 °C. Ruettinger and coworkers452 reported on the mechanism of aging of Pt/ceria-zirconia mixed oxide catalysts. In that case, the authors followed the activity of a 2% Pt/Ce02-Zr02 catalyst at 228 °C in a feed containing 5.92% CO, 7.4% C02, 31.82% H2, 28.86% N2, and 26% H20, and observed the deactivation data tabulated in Table 86. 

The application of the SEA approach to other systems is straightforward, and involves the three steps (PZC determination, uptake-pH survey, and tuned reduction) demonstrated in the earlier sections. It has recently been suggested that electrostatic adsorption over silanol groups is the cause for metal overexchange in low-aluminum zeohtes [61], It is presently being employed to study noble metal uptake on pure oxides of titania, ceria, zirconia, and niobia. 

C. Bozo, N. Guilhaume, and J.-M. Herrmann, The role of the ceria-zirconia support in the reactivity of platinum and palladium catalysts for methane total oxidation under lean conditions, J. Catal. 393, 393 06 (2001). 

P Ratnasamy, Crystalline, mesoporous ceria—zirconia based reforming catalysts for PEM fuel cells. Preprints Symp.—Am. Chem. Soc., Div. Fuel Chem. 46,635—640 (2001). 

A. Martinez-Arias, M. Femandez-Garcia, C. Belver, J. C. Conesa, and J. Soria, EPR study of oxygen handling properties of ceria, zirconia and Zr—Ce (1 1) mixed oxide samples, Catal. Lett. 65,197-204 (2001). 

The presence of oxygen enhances the catalyst stability. Breen et al. [187] investigated SRE over a range of oxide-supported metal catalysts. They concluded that the support plays an important role in the reaction. In fact, they observed that alumina-supported catalysts are very active at low temperatures for dehydration of ethanol to ethylene, which at higher temperatures (550 °C) is converted into H2, CO and CO2 as major products and CH4 as a minor product. The activities of the metal decrease in the order of Rh > Pd > Ni PS Pt. Ceria/zirconia-supported catalysts are more active and exhibit 100% conversion of ethanol at high space velocity and high temperature (650 °C). 

The order of activity at higher temperatures is Pt fs Rh > Pd. By using a combination ofa ceria/zirconia-supported metal catalyst with the alumina support, it was observed that the formation of ethene does not inhibit the steam reforming reaction at higher temperatures. 

So far only steady-state kinetics have been discussed. It is also important to include a description of oxygen storage into the model. Oxygen storage components (OSC) in the catalyst, typically ceria-zirconia, serve to store and... 

Oxides other than ceria and ceria-zirconia are very effective supports for gold in the water-gas shift, perhaps even better, but there is no agreement as to the comparative merits of ceria and titania (compare Table 10.1 and Ref. 43). We need not suppose that the same mechanism will operate in all cases, and indeed it seems unlikely that Au + ions will actually dissolve in... 

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