Ceria-lanthana catalysts

Karatzas et al. [34] performed autothermal reforming of tet-radecane, low sulfur, and Fischer-Tropsch diesel in a monolithic reformer over rhodium/ceria/lanthana catalyst. The reformer had a thermal power output of 14 kW. It was composed of an inert zirconia-coated alumina foam for feed distribution at the reactor inlet and two 400 cpsi cordierite monoliths coated with the catalyst switched in series. At an O/C ratio of 0.45, a S/C ratio of 2.5 and temperatures exceeding 740°C, full conversion of the low sulfur feed was achieved, while the formation of the byproduct ethylene was between 100 and 200 ppm. As shown in Figure 14.7, an increasing S/C ratio suppresses ethylene formation. The catalyst showed stable performance for 40 h duration. Karatzas et al. [44] determined experimentally as shown in Figure 14.8 that the efficiency of their ATR increased with increasing fuel inlet temperature and O/C ratio. 

In contrast, ceria supported catalysts show little response to the r-o-r procedure, but ytterbia ceased to be a methanator and showed trends similar to lanthana. Holmia is the only REO which so far has not produced significant lower olefin selectivity, either as prepared or following the r-o-r procedure. 

Figure 6. Initial selectivity to 4-methylpent-1-ene as a function of the ns/nA ratio. Full symbols refer to the sanqjles investigated in the present work. Open symbols represent previously investigated catalysts pure and doped zirconias (squares) [4] pure and doped cerias and lanthanas (circles) [5] ceria-zirconia solid solutions (triangles) [6] zirconias prqiared via sol-gel (reversed triangles) [7] ceria-lanthana solid solutions (diamonds) [8].

Lanthana is supposed to be superior to ceria as a washcoat stabilizer, but for oxygen storage, ceria is most effective. The market for auto exhaust catalysts is extensive with over several million units being produced each year in the world, but the rare earth content is only of the order of several grams. 

There is an obvious overlap among various applications categories. An example of the overlap is alumina which is both a structural refractory ceramic as well as a catalyst support. The additives modify the interconversion of various AI2O3 phases and the high surface area of y-Al203 is maintained by the added 3 wt% ceria or lanthana. Additives like yttria stabilize zirconia with respect to inertness and mechanical stability. Addition of yttrium or lanthanide to Fe-Cr-Al alloys reduces the spallation of oxide film. 

Most of the current converters consist of a flow-through ceramic monolith with its channel walls covered with a high-surface-area 7-AI2O3 layer (the washcoat) which contains the active catalyst particles. The monolith is composed of cordicrite, a mineral with the composition 2MgO 2AI2O3 5Si02. The chemical composition of a modern TWC is quite complex. In addition to alumina, the washcoat contains up to 30 wt% base metal oxide additives, added for many purposes. The most common additives are ceria and lanthana in many formulations BaO and Zr02 are used, and in some converters NiO is present. The major active constituents of the washcoat are the noble metis Pt, Pd, and Rh (typically 1-3 g). Most of the TWC systems in use today are still based on Pt and Rh in a ratio of about 10 1. 

Alvarez-Galvan, M.C., Navarro, R.M., Rosa, F., Briceno, Y., Ridao, M.A., and Fierro, J.L.G. Hydrogen production for fuel cell by oxidative reforming of diesel surrogate Influence of ceria and/or lanthana over the activity of Pt/Al203 catalysts. Fuel, 2008, 87 (12), 2502. 

The interaction of ruthenium carbonyl, Ru3(C0)j2 with rare earth oxides of high surface area, >50rrrg"l, has been studied. [Ru3(u H)(C0)jq(ii-0M=)] is formed on holmia, but on lanthana only [Ru(C0)o]n species are observed. Reduction of the carbonyl ligands takes place at <573K to give catalysts for the hydrogenation of carbon monoxide with activity and selectivity dependent on the particular rare earth oxide and pretreatment. Over ceria, the product is up to 55 wt% C2-5 olefins. A similar selectivity is obtained over lanthana only after redispersion through a reduction-oxidation-reduction cycle. 

Previous results [4-8] for the same reaction on zirconia-, ceria-, and lanthana-based catalysts showed a correlation between the acid-base properties (in terms of both the concentration and the strength of the sites) of the samples and their catalytic behaviour. When the number of the acid sites is sensibly higher than that of the basic ones, the main product is the undesired 2-alkene, which forms through an El mechanism (Saytzeff orientation). The alcohol adsorbs on the oxide surface through the interaction between the OH group and an acid site the rupture of the C-OH bond leads to the carbocation which mainly gives the... 

Zirconia, lanthana, and ceria have been recently reported as promoters of methane reforming reactions. Incorporation of a 5 wt% ZrOg to a base Ni/SiOg catalyst resulted in excellent performance for the reforming of methane with a CO2+ O2 mixture in a fluidised bed reactor. A conversion of CH4 near thermodynamic equilibrium and low Hg/CO ratio (l

catalyst deactivation for 10 h on-stream, in a most energy efficient and safe manner. It has been argued that Zr02 could promote the dispersion of Ni on the silica substrate, which has a direct effect on its reduction behaviour, COg adsorption and catalytic... 

Karatzas et al. [34] investigated the performance of rhodium catalyst containing 3 wt.% rhodium, 10 wt.% ceria, 10 wt.% lanthana on alumina carrier for the autothermal reforming of n-tetradecane, low sulfur diesel containing 6 ppm sulfur, and Fischer-Tropsch diesel over cordierite monolithic reactors. At temperatures exceeding 740°C, full conversion of the feed was achieved. 

Liang S, Veser G. Mixed lanthana/ceria nanorod-supported gold catalysts for water-gas-shift. Catal Lett 2012 142 936. 

Suzuki et al. reported catalyst development for kerosene steam reforming [254]. They prepared a 2 wt.% ruthenium catalyst supported by an alumina carrier, which was stabilised by 20 wt.% yttria, lanthana and ceria, respectively. At 800 °C reaction temperature, S/C 3.5 and 8-bar pressure the ceria stabilised sample showed the best performance in the medium term in the presence of 51 ppm sulfur in the feed. With hydrodesulfiirised kerosene the catalyst showed a stable performance for 8000-h... 

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