Doping and alumina

This is practically total above 300°C and, even at atmospheric pressure, lowers the residual CO content to less than 20 ppm and to a few ppm under pressure. It takes place in the presence of nickel base catalysts deposited on alumina and doped with chrominm oxide. The exothennicity of the reaction (Ar from 70 to 80 C/per cent CO converted) requires operation with two catalyst beds and intermediate effluent cooling. 

Besides boehmite and boehmite derived calcined alumina phases bayerite and eta alumina can also be produced via this technology. Also accessible is an almost unlimited variety of high purity mixed oxides such as silica aluminas and doped aluminas. Even other catalytic carrier materials for example, MgO can be obtained. 

There are also several proposals to use anodic aluminum oxides in producing optoelectronic devices. Porous oxides may find use as antireflecting coatings for optical pathways. Anodic alumina films doped by Eu and Tb are promising for application in electroluminescent cells for TEELs.28... 

Alumina, silica, clays, and zeolites are increasingly used as acidic or basic supports [26], Cycloaddition reactions often require Lewis-acid catalysts if good yields are to be obtained. Clay and doped silica gel catalysts have emerged as useful alternatives to the use of Lewis acids. Cycloaddition offuran (5) under solvent-free conditions, catalyzed by K10 montmorillonite, results in a decrease in the reaction time the endo-exo relationship is no different that obtained by use of classical heating (Scheme 9.2) [27]. 

Figure 4 in Ref. 216, reproduced on the right, displays Pt 4d5/2 XPS spectra from calcined alumina-supported platinum catalysts, pure (Pt/A) and doped with lanthanum (Pt/A-L), cerium... 

F NMR of Fluorine-Doped -Alumina. The samples studied 115) were high surface area aluminum oxides doped with fluorine by addition of aqueous HF to alumina and subsequent dehydration. A suflScient number of paramagnetic impurities were present in the samples to give relaxation times of the order of 0.01 second. The BET surface areas of most of the samples examined were within 20% of 250 meterVgram. 

The spray method was used to produce alumina pigments doped with Cr, Mn, and Co. In these experiments, Al(.vec-OBu)3 was mixed with solutions of the corresponding metal nitrates in. veobutoxide, the resulting liquids were nebulized, and then the droplets were hydrolyzed (76). The major purpose of these studies was to obtain inorganic pigments and to evaluate their color properties by altering the amount of dopants in the aluminum oxide matrix. For the same reason, the vanadium... 

Undoped p-alumina demonstrates a maximum conductivity and minimum activation energy when the sodium excess is around 20 to 30 mole%. Thereafter, further increase in the sodium content causes the conductivity to decrease. By contrast, P-alumina crystals doped with have a much higher conductivity than do undoped crystals. Explain these observations. 

Coordination causes electron-spin density redistribution in the N-O fragment the contribution of resonance structure II increase. The redistribution of spin density results in changes in the parallel component of the nitrogen hyperfine tensor. TEMPO and anthraquinone (AQ) have been used in this way to probe the Lewis acidity of alumina and Li and Mg doped alumina matrices.176 The differences in the Lewis acidic strength towards TEMPO and anthraquinone are discussed. An interesting study has appeared aimed to study the guest-host interaction between poly(amidoamine) dendrimers labelled with nitroxides and several porous solids including alumina.177... 

Table 1 summarises the most important results from the investigation of metal doping. In this table the results of MAP treatment are combined with effects of firing temperature and doping. As can be seen in Table 1, y-alumina membranes with pore radii as low as 2.0 nm (Kelvin radius) may be obtained after firing at 600°C. Note that an instrumental standard error of 0.5 nm (90% reliability) is common in permporometry. This technique should therefore only be used for comparison purposes and to obtain a qualitative impression of the pore-size and pore-size distribution of the material under investigation. 

Pore size distribution of a SASRA-treated y-alumina membrane. The support was treated with 5 mol-% MAP (MAP 10). The y-alumina was doped with 6 mol-% La and sintered at 1000°C for three hours. 

The pore doping approach has also been successful in maintaining small NC size dispersities. Initially, porous dip-coated alumina and titania films were fabricated and then directly immersed into aqueous solutions of NaAuCl4-2H20 so that the AuCLt ions could be incorporated into the pores of... 

Theories and principles of the characterization techniques are not described here. For consistenc), all the catatysts described in this review are referred to with the same nomenclature, although a different nomenclature is sometimes used in the cited publications. Each catalyst component (element) separated by the symbol indicates the sequence of its introduction into the catalyst formulation from right to left. Those separated by the symbol 7 between right and left belong to the support material and the elements on the support, respectively. For example, NiMo-P/Al refers to a catalyst prepared such that the phosphorus-containing precursor is loaded on the alumina support first, followed by nickel and molybdenum, which are introduced simultaneously. CoMo/Al — P refers to a catalyst in which cobalt and molybdenum are introduced simultaneously onto an alumina support doped with phosphorus-containing species. Each element may represent its oxide or sulfide forms. In all cases, A1 refers to the alumina-based support or to its hydroxide precursor. 

Nickel - molybdenum - alumina catalysts doped with fluoride and/or lithium, AlChE Symp. Ser, Tar Sand and Oil Upgrading, (eds S S. Shih and c.M- Oballa) (submitted for publication). 

Decay time measurements of EU2O3, and Tb203 doped and coated on alumina were conducted [82]. The luminescence of the alumina substrate was found to be much shorter than that of the rare-earth oxides. Differences between the decay times of the deposited and doped materials are accounted for by the stronger guest-host interaction and the absence of concentration quenching in the doped material. 

In solid-state laser materials, such as ruby (chromium doped alumina, AljOjiCr " ) (1) and emerald (chromium doped beryl, Be,Al,(Si03)5 Cr ) (2), transitions between multiplets of impurity states are utilized. These states mainly consist of 3d orbitals of the impurity chromium ions. For the analysis of these multiplet structures, the semi-empirical ligand-field theory (LFT) has been frequently used (3). However, this theory can be applied only to the high symmetry systems such as O, (or T ). Therefore, the effect of low symmetry is always ignored in the analysis based on the LFT, although most of the practical solid-state laser materials actually possess more or less distorted local structures. For example, in ruby and emerald, the impurity chromium ions are substituted for the aluminum ions in the host crystals and the site symmetry of the aluminum ions are C, in alumina and D, in beryl. Therefore, it is important to clarify the effect of low symmetry on the multiplet structure, in order to understand the electronic structure of ruby and emerald. 

The catalytic performance in the propane dehydrogenation reaction of Pt and PtSn catalysts on inert supports (like K-doped alumina and ZnAlj04, and on an acidic AljOj,) under conditions of high severity was studied by means of pulse and flow reaction techniques to determine the effect of the nature of the support on the catalytic behavior. The... 

Transparent anatase Ti02-based multilayered photocatalytic films synthesized via a sol-gel process on porous alumina and glass substrates showed a sponge-like microstructure and a mean crystallite dimension of ca. 8 nm [152]. Doping such films with iron(III) impeded the photocatalytic activity. 

Thermolum. Thermoluminescent peaks have been observed in silica powder and in vitreous silica after irradiation. One at 85° depends on doping with alumina but does not require thermal treatment (7pure silica not colored by 6 x lO ev/gm of y-rays showed an intense thermoluminescence at 280° (7S). Some or all of these centers, and oxid red as well, may belong also to earlier types. 

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