Effect of Cerium

The rare earth composition of commercial electrodes is also related to electrode corrosion. This was noted by Sakai et. al. [44], who found that the presence of Nd or Ce inhibited corrosion when substituted in part for La in La, Z (NiCoAl)5 (Z = Ce or Nd) electrodes. However no explanation for the effect was noted. Willems [22] prepared an electrode of Lao jjNdo jNij COi Sif), which retained 88% of its storage capacity after 400 cycles. He attributed its long cycle life to a low of 2.6 A.  

The case of cerium is of particular interest. Adzic et al. [43] examined the properties of a homologous series of alloys with a composition corresponding to Ltti CCvNiji j CoQ.jjMno Aloj and measured their comparative performance as battery electrodes. A PCT diagram for this system is shown in Fig. 10. 

Note that at x 0.2 there is a decrease in the H storage capacity and thermodynamic stability, until at. r = 1 the decrease in both 

Cycle-life plots for the La Ce B, electrodes are illustrated in Fig. 11. The decreased charge capacity in all Lai Ce B, alloys with x 0.35 conforms with the shorter and higher plateau pressure of the isotherms depicted in Fig. 10. The extremely low electrochemical capacity of CeB is a consequence of the 

X Vh ( A /atom ) n (H atoms/ unit cell) AV/V (%) QnViiX Corrosion (wt.% / cycle) 

X value Vh (A /atom) n, H atoms per unit cell %AVIV Qmax (mAhg-1) Corrosion (wt%/cycle) 

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Oh, S.H. (1990) Effects of cerium addition on the CO-NO reaction kinetics over alumina-supported rhodium catalysts, J. Catal. 124, 477. 

Table I. Effect of Cerium and Alumina Added to Cracking Catalyst...

The promotional effect of cerium is not confined to alumina as shown by the data for magnesia (26) in Table II. 

Results, again, show net gain over the same cracking catalyst used previously for cerium/alumina case. Cerium, moreover, seems to act as a promotor for other rare earths as could be implied from the synergistic effect observed between cerium and lanthanum (27). Our conclusions about the catalytic effect of cerium have been confirmed recently by others (28). 

Figure 9. The effect of cerium, introduced as mischmetal along with the treatment alloy, as a junction of the cerium content of the alloy (21). Compositions of the irons were 3.4-3.7% C, 2.3-2.6% Si, 0.6% Mn, 0.01-0.02% S, 0.036-...

As far as future research is concerned, one can anticipate a greater concern with the effects of the individual rare earth elements. Effects of cerium as opposed to lanthanum, or the other rare earths, may be more thoroughly researched. Perhaps the list of those elements specified by the foundry industry will eventually embrace those beyond neodymium. Nevertheless, much... 

The above observations clearly indicate the inadequacy of the simple second-order law for describing the reaction rate outside the conditions of strongly acidic solutions and low initial cerium(III) concentrations. A more general rate law, suggested by considerations of the reaction mechanism (see Discussion), which takes into account the inhibiting effect of cerium(III), is of the form... 

Figure 4. Effect of cerium(III) on cerium(IV) -cis-Cr(0H2)2(C204)2<- reaction in 0.950M sulfuric acid...

Not until similar information is obtained on the effect of cerium(III), hydrogen ion, and sulfate ion on the oxidations of Cr(C2C>4)3 3 and Cr(OH2)4C204+, will it be appropriate to discuss the relative reactivities of the three oxalato complexes toward cerium(IV). 

Figure 11 The effect of cerium amount on the isopropylation of naphthalene over ceria modified H-mordenite. Reaction conditions catalyst, 1 g naphthalene, 200 mmol propylene pressure, 0.8 MPa temperature, 300 °C period, 4 h.

In conclusion, there is overwhelming evidence for the beneficial effect of cerium oxide on the activity of the noble metal catalyst. However, the nature of the promoter effect of ceria is not fully understood. Most likely, the noble metal-cerium oxide interface is of crucial importance for some of the effects observed. More studies with model systems are needed for a better understanding of the promoter effects of ceria. 

Zhuang, Q., Qin, Y., and Chang, L. Promoting effect of cerium oxide in supported nickel catalyst for hydrocarbon steam-reforming. Applied Catalysis, 1991, 70 (1), 1. 

The objective is to study the effect of cerium introduced in USY zeolite and the resistance of these modified catalysts to vanadium in steam. 

For Cr-containing catalysts, the stabilizing effect of Ce and La is not so evident, since Cr ions appeared to be weak mineralizations at their content less than 10% and the temperatures below 1273 K [8]. When Cr is supported on Ce-containing alumina, the stabilizing effect of cerium is enhanced by Cr. The quantity of a-Al203 formed vs Cr concentration with respect to the absolute value becomes comparable with La effect (Fig.l, A, B). 

Imamura S, Shono M, Okamoto N, Hamada A. Ishida S (1996) Effect of cerium on the mobility of oxygen on manganese oxides. Appl. Catal. A 142 279—288. 

Guergova, D., Stoyanova, E., Stoychev, D., Avramova, L, Stefanov, P., (2011). Investigation of the inhibiting effect of cerium ions on the corrosion behaviour of OC404 stainless steel in sulfuric acid medium. Open Corrosion Journal in press, ISSN 1876-5033... 

Pokrovski KA, Rhodes MD, Bell AT (2005) Effects of cerium incorporation into zirconia on the activity of Cu/Zr02 for methanol synthesis via CO hydrogenation. J Catal 235 368-377... 

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