Mesoporous ceria catalysts

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). 

Mesoporous ceria and ceria-zirconia powders with high surface area have also been prepared using a surfactant-assisted method to prepare catalysts containing Ce02... 

In 2012 Idakiev et al. [120] investigated the Au supported on ceria-modified mesoporous zirconia catalysts for the WGSR. The WGS activity of various Au-supported mesoporous zirconia and ceria-modified mesoporous zircOTiia catalysts are presented in Figure 3.23. 

Ceria-modified mesoporous zirconia catalysts show much higher activity than pure mesoporous zirconia catalysts especially at lower reaction temperatures. The characterization results reveal that ceria decreases the degree of zirconia crystallinity and particle size. Also ceria interacts with the mesoporous zirconia and causes the strong effect on the reducibility of the support. The high and stable WGS activity could be related to the high stability of the gold dispersion and to larger number of active sites located at the Au/ceria-modified mesoporous zirconia interface. 

Idakiev et al. [137] reported mesoporous ceria and nanorods Ce02 for the Au catalysts for WGSR. Both mesoporous- and nanorod-supported catalysts exhibit higher activity than regular Au/Ce02. Of the mesoporous- and nanorod-supported catalysts, mesoporous-supported catalyst exhibited higher activity. 

Fig. 3 depicts the N2 adsorption-desorption isotherms (A) and pore size distribution (B) of the samples. The shape of the isotherms (Fig. 3A) and the pore sizes did not change significantly (Table 1), meaning that material kept its mesoporous structure after introduction of the ceria. The pore diameters of the support and the gold loaded catalysts, both calcined at 400 °C, are practically... 

Fig. 3. Niteogen adsorption isotherms (A) and the corresponding BJH pore size distribution curves (B) of the mesoporous titania as-prepared (MTi02 80), modified by ceria mesoporous titania support as-prepared (CeMTi 80) and calcined at 400 °C (CeMTi 400), and gold-based catalysts calcined at 400 °C with different gold content (2 Au/CeMTi 400 and 5 Au/CeMTi 400).

Formation of dispersed phase of ceria in the dealuminated mordenites modified with ceria/cerium was registered by XRPD. Decrease in acidity at increased content of ceria may be prescribed to ion-exchange of protons with cerium cations. An extra mesoporous structure of ceria at higher metal loading (more than 10 wt. %) was found. On one side, a lower acidity and narrower channels of catalysts resulted in the lower catalytic activity, on the other side higher selectivity to the desired 4,4 -dialkylated biphenyl was achieved. 

V. Idakiev, T. Tabakova, K. Tenchev, Z.-Y. Yuan, T.-Z. Ren, B.-L. Su, Gold nanoparticles supported on ceria-modified mesoporous titania as highly active catalysts for low-temperature water-gas shift reaction, Catal. Today 128 (2007) 223-229. 

Other molecules present in the gas mixtures like alcohols or ketones may have a moderate effect on aromatic oxidation but the reverse (inhibition of alcohol oxidation by aromatics) is most often observed. Different supports of Pt were used for toluene oxidation Al203, Al203/Al, Zn0/Al203, Ti02, mesoporous fibrous silica or monoliths. Zeolites, generally promoted by platinum, were shown to give excellent catalysts for aromatic oxidation. Basic zeolites showed excellent performances in oxidation of m-xylene even in the absence of platinum. Palladium catalysts, either supported on alumina or ceria-alumina, were also investigated for oxidation of benzene and several alkylbenzenes. ... 

There has been much recent interest in the preparation of various inorgairic solids (notably aluminium phosphates) with controlled porosity in the microporous and mesoporous range [1], in ways analogous to that used in the synthesis of aluminosilicate zeolites. For the synthesis of mesoporous solids, the synthetic paths make use of long chain surfactant molecules. At the University of Cyprus there is a long-standing interest in the synthesis and study of porous ceria [2-4], because of the importance of that solid in several catalytic applications, and notably in automobile exhaust catalysts. In this presentation we discuss the use of aniline as the precipitating base instead of ammonia, which has hitherto been used. 

We have been interested in the synthesis and study of porous ceria, because of its importance in several catalytic applications, and notably in automobile exhaust catalysts [1,2,3]. Work so far, has indicated that ceria or metal-doped ceria prepared from dilute aqueous solutions by ammonia precipitation, is mesoporous [4-6]. The surface texture of these solids (BET surface area, size and shape of pores, total pore volume) is susceptible to changes in synthesis conditions such as pH and concentration of the cerium and other cation precursors used. For several cations used, a lowering of the BET surface area of ceria was obtained. However, for several metallic cations, including manganese, a significant increase in BET surface area was obtained. 

Often, there is a correlation between acidic/basic or red-ox properties of some solid material and its ability to adsorb or catalytically convert certain pollutant. For example, acidity of different zeolites and mesoporous materials is important for their ability to adsorb aldehydes and ketones (from the gas phase) or phenol and nicotine (from the aqueous phase) [40, 43]. Red-ox properties are often correlated with catalysts efficiency for example, red-ox features of ceria-based mixed oxides are of importance for their ability to catalyse direct conversion of methane to synthesis gas, and they can be affected by incorporation of Zr02 [44]. The oxidability of mixed oxides is an important feature, which determines the possibility of their use as catalysts for combustion reactions and it can be also determined using TPR-TPO techniques [45]. 

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