Catalysts cerium

From the early 1960s onwards, the use of lanthanide (Ln) based catalysts for the polymerization of conjugated dienes came to be the focus of fundamental studies [31]. The first patent on the use of lanthanides for diene polymerization originates from 1964 and was submitted by Union Carbide Corporation (UCC) [32,33]. In this patent the use of binary lanthanum and cerium catalysts is claimed. Soon after this discovery by UCC, Throckmorton (Goodyear) revealed the superiority of ternary lanthanide catalyst systems over binary catalyst systems. The ternary systems introduced by Throckmorton comprise a lanthanide compound, an aluminum alkyl cocatalyst and a halide donor [34], Out of the whole series of lanthanides Throckmorton... 

At the start, the cycle begins with a certain amount of Ce+4 ions. The second reaction provides Br- ions, which inhibit the first reaction. This leads to an increase in concentration of Ce+3. After reaching a certain amount of Ce+3, the oxidation reaction starts, since little Ce+4 remains. The system can no longer produce sufficient Br to inhibit the reaction, and Ce+3 decreases rapidly, producing Ce+4 until the cycle is completed. It is possible to maintain indefinite oscillations with constant frequency in a continuous flow stirred reactor into which bromate, malonic acid, and cerium catalyst are being supplied at a uniform rate. 

The influence of the inlet concentration of NO was studied with four soot samples mixed with a supported platinum catalyst (I wt% Pi on ASA) at 650 K. The oxidation rate at 50% soot conversion is plotted as a function of the NO inlet concentration in Figure 12.2.a. From this figure it is clear that the influence of the NO concentration on the oxidation rate of the synthetic Printex-U and the diesel soots activated with copper or iron is comparable. There is a first order relation between the NO inlet concentration and the oxidation rate. For cerium activated soot, there is also a first order relation between the NO inlet concentration and the oxidation rate. In this case, however, the effect of NO is approximately twice as large as is the case with Printex-U, Phntex-U with a physical mixture of a cerium catalyst (not shown), and copper- or iron-activated soot. 

The addition of a separate cerium catalyst has only a minor effect on the soot oxidation rate both in the presence of Oj and O/NO2. 

The use of CeOs-based materials in catalysis has attracted considerable attention in recent years, particularly in applications like environmental catalysis, where ceria has shown great potential. This book critically reviews the most recent advances in the field, with the focus on both fundamental and applied issues. The first few chapters cover structural and chemical properties of ceria and related materials, i.e. phase stability, reduction behaviour, synthesis, interaction with probe molecules (CO. O2, NO), and metal-support interaction — all presented from the viewpoint of catalytic applications. The use of computational techniques and ceria surfaces and films for model catalytic studies are also reviewed. The second part of the book provides a critical evaluation of the role of ceria in the most important catalytic processes three-way catalysis, catalytic wet oxidation and fluid catalytic cracking. Other topics include oxidation-combustion catalysts, electrocatalysis and the use of cerium catalysts/additives in diesel soot abatement technology. 

The highly exchanged cerium catalysts exhibited an initial deceler-atory period in the 1-butene isomerization. This may be caused by some strong sorption of the butene molecules which would be expected at the low reaction temperatures used for CeX-I and CeX-II and with the high fields associated with Ce " ions in surface sites. Such sorption might lead to a reduction in the number of sites for catalysis. 

Figure 1. Wet air oxidation. Magnesium-cerium catalysts with different mass ratios as defined above. Conversion of phenol as a function of time.

The fresh catalysts were analysed by BET, XRD and TPR techniques. BET analyses show clear differences in the surface area, pore volume and pore size distribution between cerium catalysts (A and B) (Fig. 1). Pore distribution and morphological parameters of catalyst B are similar to those of pure Zr02 (23 m /g for Zr02 and 22 m /g for support B), whereas the surface area of catalyst A is markedly higher (71 mVg). 

Br2 then brominates the organic acid. This reaction depletes Br- and lets a second pathway take over that starts with a self-accelerating two-step sequence that also oxidizes the cerium catalyst and so produces the color change ... 

The CeY zeolite is utilized for the preparation of 4-methylcoumarin by the reaction of phenol with AAN. The formation of PA represents the first step the subsequent acylation at the ortho position, followed by an intramolecular aldol-like condensation, affords the final 4-methylcoumarin in 75% yield (Scheme 5.8). In the entire process, the cerium-catalyst shows a bifunctional character the active centers in the supercage of CeY zeolite, the Ce + ions, act as Lewis acid catalysts, whereas the acid centers H+, formed by the dissociation of water according to the equation Ce + + H2O [Ce(OH)]2+ + H+, act as Bronsted catalysts. 

In order to compare the rate of reaction (P5) for various perturbants we carried out qualitative experiments where one of the perturbants (at a concentration of 9.37-10 mol dm ) and all the BZ reagents, except for the Ce(IV), have been premixed for two hours. Our hypothesis was that due to (P5), in the absence of the catalyst, some BrMA should accumulate, which would shorten or eliminate the induction period. It has been found that, for PEG-2000 after two hour premixing, on addition of the cerium catalyst, the system immediately starts to oscillate. For both the other two PEGs used a decrease in the IP was observed, while in the case of MPEG-2000 the IP slightly decreased and with EG the IP is unaffected. 

This equation cannot explain the most striking feature of the BZ reaction, namely the periodic changes in the color of the solution when the reaction proceeds. The equation does not explain the role played by the cerium catalyst or by the bromide ions that are added before the start of the reaction. A careful examination of the reaction mechanism is therefore necessary. Three processes are of importance Process A consumption of bromide ions Process B formation... 

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