Alumina doping

Figure 14. Resistivity of p" -alumina doped with zirconia.

An alternative preparation of benzofurans was carried out via a microwave-assisted Mannich condensation of paraformaldehyde and a secondary amine followed by cyclization with an alkynyl phenol 185 mediated by alumina doped with Cul (Scheme 67). The reaction can be carried out in a single-step... 

This approach may find application in peptide bond formation that would eliminate the use of irritating and corrosive chemicals such as trifluoroacetic acid and piperidine as has been demonstrated recently for the deprotection of N-boc groups (Scheme 6.7) a solvent-free deprotection of N-tert-butoxycarbonyl group occurs upon exposure to microwave irradiation in the presence of neutral alumina doped with aluminum chloride (Scheme 6.7) [41]. 

One of the most attractive features of borohydride reductions is that under micro-wave-enhanced conditions they can be performed in the solid state, and rapidly. We were attracted by the work of Loupy [57], and in particular Varma [58, 59] who has shown that irradiation of a number of aldehydes and ketones in a microwave oven in the presence of alumina doped NaBH4 for short periods of time led to rapid reduction (0.5-2 min) in good yields (62-93%). In our study [60] seven aldehydes and four ketones were reduced (Tab. 13.3). Again reduction was complete within 1 min, the products were of high purity (>95%), of high isotopic incorporation (95%, same as the NaBD4) and the reactions completely selective. 

The atmosphere is also important in sintering. Gas trapped in closed pores will limit pore shrinkage unless the gas is soluble in the grain boundary and can diffuse from the pore. Alumina doped with MgO can be sintered to essentially zero porosity in hydrogen or oxygen atmospheres, which are soluble, but not in air, which contains insoluble nitrogen. The density of oxides sintered in air is commonly less than 98% and often only 92-96%. The sintering atmosphere is also important in that it may influence the sublimation or the stoichiometry of the principal particles or dopants. 

ZFS can be obtained from powder samples of Fe(III) and Gd(III) alumina doped at the 0.1% level. The ZFS is of the same order as the X-band quantum but by 130 GHz the analysis was straightforward and the sign and magnitude of the ZFS parameters could be determined. 

Sato, E., Morioka, H., Kuribayashi, K., and Sundararaman, D., Effect of small amount of alumina doping on superplastic behaviour of tetragonal zirconia , J. Mater. Sci., 1999, 34, 4511-18. 

Table 1 Influence of support treatment, y-alumina doping, membrane firing temperature and SASRA-...

Spray drying is used for obtaining cracking catalysts in the form of microbcads (silica-alumma or silica alumina doped with 5 15% of X or Y molecular sieves exchanged with rare earth) Figure 2a and 2b show two different kinds of particle obtained by different atomizations of a given feed to a spray dryer... 

On the other hand, heterogeneous systems using tin oxide and alumina doped with tin and zinc oxides are active for soybean oil methanolysis, with the advantage of no emulsion formation at the end of the reaction. These catalysts not only present high conversion yields (up to 93% in 3 hours) but it is also possible to recycle them without any loss in catalytic activity. For this reason, it is reasonable to assume that these catalysts could be economically viable for use in large scale biodiesel production. 

Alumina-catalyzed ckavage of epoxides (6,16-17 8,10-12). The nucleophilic opening of epoxides by alcohols can also be promoted by alumina used in catalytic amounts. The reaction then requires higher temperatures and longer reaction periods, but is economical for large-scale preparation. The reaction of cydohexene oxide with allyl alcohol (equation I) can be carried out on 0.3 moles of the oxide with only 3 g. of W-200-N alumina as purchased. The yield is the same as that obtained with large quantities of alumina doped with 4 weight % of the alcohol. 

A long list of oxides was prepared sonochemically. Almost all the above-mentioned oxides were synthesized in organic solvents. The other oxides that will be discussed from here on were all prepared in aqueous solutions. Submicron size spheres of silica and alumina prepared by well-known methods were coated sonochemically by nanoparticles of oxides of europium and terbium using the same concentration of ions [81]. We have also used sonochemistry to prepare nanoparticles of silica and alumina doped with the same rare-earth ions for comparison. The highest luminescence intensities were observed for europium and terbium doped in nanoparticles of alumina of dimension 20-30 run. The intensities are comparable or higher than in commercial phosphors. 

The concentrations of donor centres that cause the creation of an anion radical from adsorbed nitrobenzene molecules are given in Table 3. They have been established on an MgO surface doped with different alkali metals and on silica and alumina doped with metallic solution. 

Catapal B y-alumina doped with copper, zinc, or both copper and zinc were used for mechanistic studies. All three samples were prepared by incipient wetness impregnation, with Zn(N03)2 and Cu(N03)2 as precursors, followed by calcination in air at 500 C for 4 hours. 

Temperatures in °C pure alumina doped alumina pure alumina doped alumina... 

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