Lanthanum oxide, catalyst

Figure 4.21 The La/Ai intensity ratio from LEIS spectra for a series of alumina-supported lanthanum oxide catalysts of different loadings as a function of the pretreatment temperature indicates that the lanthanum oxide spreads over the alumina surface at high temperatures (from van Leerdam el al. [53]).

Borchert, H. and Baerns, M. The effect of oxygen-anion conductivity of metal oxide-doped lanthanum oxide catalysts on hydrocarbon selectivity in the oxidative coupling of methane. J. Catal 1997,168, 315-320. 

Borchert, H. Baemsy, M. The Effect of oxygen-Anion Conductivity of Metal-Oxide Doped Lanthanum Oxide Catalysts on Hydrocarbon Selectivity in the Oxidative Coupling of Methane, y. Catal. 1997, 168,315-320. 

Conway, S. J., Greig, J. A. Thomas, G. M. (1992). Comparison of lanthanum oxide and strontium-modified lanthanum oxide-catalysts for the oxidative coupling of methane. Appl. Catal. A Gen., 86,199-212. 

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

The catalyst was prepared by impregnating porous alumina particles with a solution of nickel and lanthanum nitrates. The metal loading was 20 w1% for nickel and 10 wt% for lanthanum oxide. The catalyst particles were A group particles [8], whereas they were not classified as the AA oup [9]. The average particle diameter was 120 pm, and the bed density was 1.09 kg m . The minimum fluidization velocity was 9.6 mm s. The settled bed height was around 400 mm. The superficial gas velocity was 40-60 mm s. The reaction rate was controlled by changing the reaction temperature. 

To finish with another trend for NO removal consisting in NO direct decomposition, we would like to depict the infrared study of NO adsorption and decomposition over basic lanthanum oxide La203 [78], In this case, the basic oxygens are proposed to lead to N02 and N03 spectator species, whereas the active sites for effective NO decomposition are described as anion vacancies, which are often present in transition metal oxides. This last work makes the transition with the study of DeNO, catalysts from the point of view of their ability to transfer electrons, i.e. their redox properties. 

Lanthanum cobaltate catalysts carbon monoxide oxidation, kinetics, 36 281-283... 

Perovskites, 27 358 band structure, 38 131-132 crystal structure, 38 123-125 Perovskite-type oxides see also specific lanthanum-based catalysts actinide storage in radioactive waste, 36 315-316... 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

The rare earth oxides have a number of distinguishing properties important in catalytic applications. The oxides are basic O) compared to alumina, lanthanum oxide (La203) being the most basic. The oxides also have good thermal stability, a valuable characteristic in most industrial applications. Some rare earths including cerium, praseodymium, and terbium form non-stoichiomet-ric oxides ( ), an important property shared by many good oxidation catalysts. These mixed valence state compounds are typically polymorphic. 

Recent studies of the kinetics and mechanism of n-butene isomerization over lanthanum oxide by Rosynek et al. (28) indicate that for this catalyst interconversion of the two 2-butene isomers (s4 in Example 8) is very slow and in that case the system could be described by mechanism m3. Studies by Goldwasser and Hall (29) indicate that as temperature is increased, there is appreciable direct conversion via s4 so that one or both of the other two direct mechanisms may be involved. These authors suggest that further studies with all three isomers, at several temperatures and with tracers, would be desirable. 

Lanthanum oxide is well-known as an active isomerization (406) and hydrogenation catalyst (407), and it has attracted much attention recently (along with other basic oxides, such as MgO and CaO) as a catalyst for the oxidative dehydrogenation and coupling of methane to C2 hydrocarbons (408-410). Its activity for selective NO reduction of CH4 in excess oxygen has also been demonstrated (411, 412). 

Fig. 10.12. LEIS spectra of La203/Al203 catalysts after calcination at 825 and 1325 K, taken with a 3 keV He+ beam indicate that lanthanum oxide spreads over alumina at high temperatures (from...

Inui found an accelerating efiect of CO on carbon dioxide methanation over a supported nickel lanthanum oxide ruthenium catalyst [158] and a systematic comparison of the catalytic efficiencies of the atumina supported noble metals Pi, Pd, Kh. Ir and Ku was reported by Solymosi [tS9. He found that (he specific rates for the formation ofCH decrease in the order Ru > Kh > Pt - Ir - Pd. 

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