Ceria catalyst

Jacobs, G., Crawford, A., Williams, L., Patterson, P.M., and Davis, B.H. 2004. Low temperature water-gas shift Comparison of thoria and ceria catalysts. Appl. Catal. A Gen. 267 27-33. 

Bazin et al.447 applying infrared spectroscopy and CO adsorption to a Pt/ceria catalyst, assigned a band at 1937 cnC1 on the reduced catalyst to a bridging CO species bound between both the support and Pt particle. 

Table 69 Kinetic parameters from fixed bed testing of metal/ceria catalysts at 300 °C386... 

Flytzani-Stephanopoulos and coworkers—urea method for preparing high surface area ceria/substituting noble metals with base metals/cationic active sites for Au and Pt-ceria catalysts/deactivation by hydroxycarbonates and improved stability with 02 co-feeding. Li et al.396 reported on low temperature water-gas shift catalysts in their search for a replacement catalyst for Cu/ZnO suitable for use in a fuel... 

In 2006, Deng and Flytzani-Stephanopoulos450 included a small amount of ( 1 %02) in the water-gas shift feed and indicated that both the Au/ceria and Pt/ ceria catalysts were able to recover from the shutdown condition, and TPO tests... 

Table 72 CO conversion data over l%Pt/ceria catalysts with varying BET surface area. 1.5%CO 50% H2O 40%H2, balance N2 at SV = 435 000 cm3/g per hour407...

Table 73 CO conversion data over metal/ceria catalysts with equivalent molar amounts of metal (l%Pt by weight as basis). GHSV = 21.7 L/g, per hour. BET SA ceria = 105.5 m2/g410 ... 

While Au promoted reduction of ceria to a lower temperature than Pt, both 5% loaded catalysts led to reduction of the ceria surface shell by heating in H2 to 200 °C. However, 20 times the amount of Au/ceria catalyst was required to achieve the same lightoff curve as was obtained with Pt/ceria, indicating that the Pt/ceria catalyst was much more active (Table 78). As previously observed with Pt, increasing the loading of Au did increase the CO conversion rate, as shown in Table 79. To help explain the observed differences in the water-gas shift rates observed for the two different promoters, transient formate decomposition tests in the presence of steam432 were... 

The authors also pointed out that the Pt/ceria catalysts were much more stable than the Au/ceria and Au/Fe203 catalysts, and that the addition of 40% H2 to the feed caused the Au catalysts to rapidly lose activity. In a test with 2%CO, 20%H2O, and helium, the Pt/ceria catalyst retained activity at over 85% conversion, while Au/ ceria dropped from 65% to <10% during 3000 min. Au/Fe203 deactivated from 50% to about 40%. 

The metal/ceria catalyst was suggested to possibly follow the simplified mechanism in Scheme 83, with H20 activation on ceria, CO adsorption on the metal, with reaction across the metal-ceria interface. 

Bera and co workers421 reported on a combustion-synthesized Cei xPtx02 catalyst, where a high fraction of Pt was suggested to be dispersed as Pt2+ ions. Based on XPS results before and after reaction, the authors concluded that the Pt ions were likely the active sites for the WGS reaction. The l%Pt/ceria catalyst was prepared using a combustion mixture of (NH4)2Ce(N03)6, H2PtCl6 and C2H6N402 in the... 

Liu, Ruettinger, Farrauto, and coworkers—loss of catalytic activity during shutdown/restart cycles linked to formation of carbonates. Liu and coworkers435 at Engelhard reported on the loss of catalytic activity when Pt/ceria catalysts were exposed to shutdown/restart cycles. Utilizing DRIFTS spectroscopy, the authors... 

Kim and Thompson—site blocking by formates/carbonates over Au/ceria catalysts linked to deactivation. Kim and Thompson437 reported on the deactivation of Au/ceria catalysts. The ceria was prepared by the decomposition of cerium carbonate (BET SA ceria calcined at 400 °C = 203 m2/g) or obtained from Rhodia (BET SA ceria calcined at 400 °C = 155 m2/g). Au was added by precipitation of HAuC14, resulting in a particle distribution between 1 and 10 nm, with the majority of clusters between 2 and 7 nm, as examined by HR-TEM. The experimental catalyst was tested with respect to the Sud-Chemie water-gas shift catalysts, consisting of Cu-Zn-Al with surface area 60 m2/g, and results are reported in Table 87. 

To gain insight into the nature of the deactivation behavior, the authors used the 5% Au/ceria catalyst prepared using the Rhodia support, and examined changes in... 

Table 88 CO conversion over 30%Cu-l%Pd/ceria catalyst prepared by IWI of the metals at 210 °C as a function of feed type, using 4%CO, 10%CO2, C0/02 = 1/0.5, and CO/H20 = 1/10, balance H2 with 0.5 ml of catalyst438...

Catalyst systems for the WGS reaction that have recently received significant attention are the cerium oxides, mostly loaded with noble metals, especially platinum 42—46]. Jacobs et al. [44] even claim that it is probable that promoted ceria catalysts with the right development should realize higher CO conversions than the commercial Cu0-Zn0-Al203 catalysts. Ceria doped with transition metals such as Ni, Cu, Fe, and Co are also very interesting catalysts 37,43—471, especially the copper-ceria catalysts that have been found to perform excellently in the WGS reaction, as reported by Li et al. [37], They have found that the copper-ceria catalysts are more stable than other Cu-based LT WGS catalysts and at least as active as the precious metal-ceria catalysts. 

The copper-ceria catalysts in WGS were found to be nonpyrophoric and stable, showing little or no deactivation during the experiments. The Civ,2Ce(J802 y catalyst prepared by coprecipitation method showed good catalytic activity for the WGS reaction. The Cu0, Ce0 902 v catalysts prepared by the sol-gel method were found to be less active, which could be due to the lower number of active... 

A. Martinez-Arias, M. Femandez-Garcia, L.N. Salamanca, R.X. Valenzuela, J.C. Conesa, and J. Soria, Stmctural and redox properties of ceria in alumina-supported ceria catalyst supports, J. Phys. Chem. B 104, 4038 046 (2000). 

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