Lanthanum oxide

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). 

In addition to platinum and related metals, the principal active component ia the multiflmctioaal systems is cerium oxide. Each catalytic coaverter coataias 50—100 g of finely divided ceria dispersed within the washcoat. Elucidatioa of the detailed behavior of cerium is difficult and compHcated by the presence of other additives, eg, lanthanum oxide, that perform related functions. Ceria acts as a stabilizer for the high surface area alumina, as a promoter of the water gas shift reaction, as an oxygen storage component, and as an enhancer of the NO reduction capability of rhodium. 

Four years before isolating yttria, Mosander extracted lanthanum oxide as an impurity from cerium nitrate (hence the name from Greek XavOaveiv, to hide), but it was not until 1923 that metallic lanthanum in a relatively pure form was obtained, by electrolysis of fused halides. 

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. 

Lanthanum oxide is valence invariant, and does not exhibit any oxygen storage capacity, but it effectively stabilizes 5/-AI2O3. It spreads over the alumina surface and provides a barrier against dissolution of rhodium in the support. 

E. Morrice, C. Wyche and T. A. Henrie, Electrowinning Molten Lanthanum from Lanthanum Oxide,... 

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. 

Aluminium oxide, arsenic trioxide, bismuth trioxide, calcium oxide, chromic oxide, lanthanum oxide, lead dioxide, magnesium oxide, manganese dioxide, molybdenum trioxide, phosphorus pentoxide, stannic oxide, sulfur dioxide (explodes), tantalum pentoxide, tungsten trioxide, vanadium pentoxide. 

W. A. Roth, U. Wolf, and O. Fritz, The Heat of Formation of Aluminum Oxide (Corundum) and of Lanthanum Oxide, Zeit. Elektro. u. Angew. Physik. Chemie, 46,42 (1940). 

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]).

Regeneration of the active sites in the vicinity of lanthanum oxide... 

Langmuir isotherm equation phys chem An equation, useful chiefly for gaseous systems, for the amount of material adsorbed on a surface as a function of pressure, while the temperature Is held constant, assuming that a single layer of molecules is adsorbed it is / = ap/ 1 + ap). where / is the fraction of surface covered, p is the pressure, and a is a constant. lar),myur Ts-3,th3rm i,kwa zh3n ) lanthana See lanthanum oxide. lan tha-na ... 

Lanthanum is a soft silvery-white metal that, when cut with a knife, forms an oxide with the air (tarnishes) on the exposed area. It is the most reactive of the elements in the series. It reacts slightly with cold water but rapidly with hot water, producing hydrogen gas (H ) and lanthanum oxide (La O ). It directly interacts with several other elements, including nitrogen, boron, the halogens, carbon, sulfur, and phosphorus. 

Lanthanum oxide (2La + 30 —> La O ) is used to make high-quality glass,... 

The first, made by Ichikawa et al. [29], was the evidence that rhodium or iridium cluster carbonyls, when adsorbed on zinc oxide, titania, lanthanum oxides, zirconia or magnesia, could produce quite selectively ethanol by the Fischer-Tropsch synthesis. This was a timely discovery (metallic catalytic particles produced by traditional methods could not reproduce such selectivity) since it came at a period of geopolitical tension after the Kippur war in 1973, which caused the price of crude oil to increase enormously. Therefore, that period was characterized by intense research into selective Fischer-Tropsch catalysis. 

The experimental simplicity of Method 3 has attracted the specialists in modern trends in catalysis. Thus, in Method 3 different authors used RbF (04SC4431), MgO (09EJM3805), KF/AI2O3, mixed magnesium-aluminum carbonate, or mixed magnesium-lanthanum oxide (08TL2730) in methanol. Recently, 2-aminopyran syntheses with acetylacetone 35 and ethyl acetoacetate 36 were carried out in an ionic liquid [(bmim)(BF4), 1-butyl-3-methylimidazolium borofluoride] with 1,1,3,3-tetramethylguanidine as... 

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 production of endohedral fullerene complexes in visible amounts was first accomplished by a pulsed laser vaporization of a lanthanum oxide-graphite composite rod in a flow of argon gas at 1200 °C [66]. In this procedure, the newly formed endohedrals, together with empty fullerenes, sublime readily and are carried away in the flowing gas, depositing on the cool surfaces of the apparatus. This sublimate contains the complexes La CgQ, La C74 and La Cg2 (Figure 1.9). Among these, the endohedral molecule La Cg2 exhibits an extra stability. It can... 

Figure 1.9 FT-ICR mass spectrum of hot toluene extract produced by laser vaporization of a lanthanum oxide-graphite composite rod [66].

Another method involves heating lanthanum oxide with excess ammonium chloride at 300°C ... 

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