Aluminum distribution

Aluminum distribution in zeolites is also important to the catalytic activity. An inbalance in charge between the silicon atoms in the zeolite framework creates active sites, which determine the predominant reactivity and selectivity of FCC catalyst. Selectivity and octane performance are correlated with unit cell size, which in turn can be correlated with the number of aluminum atoms in the zeolite framework. ... 

The major effect of new advanced techniques on catalyst structure is found in zeolite catalysis. NMR techniques, especially MASNMR, have helped to explain aluminum distribution in zeolites and to increase our understanding of critical parameters in zeolite synthesis and crystallization. MASNMR, combined with TEM, STEM, XPS, and diagnostic catalytic reaction probes, has advanced our knowledge of the critical relationship between the structure and reactivity patterns of zeolites in the chemical fuels industry. Throughout the symposium upon which this book is based, many correlations were evident between theoretical quantum mechanical calculations and the structures elucidated by these techniques. 

Two types of structures were seen a needle type bundled structure pointing inward towards the center of the sphere and surface bumps. The needle type structures overall were less than 10 pm in length and less than 1 pm in thickness. To confirm that these structures corresponded to sodium alanate. elemental mapping of the alanate s sodium and aluminum constitutes was made. As can be seen in Fig.5, the presence of intense sodium distribution was noted on the needle structures while the both the surface bumps and needle structures showed the presence of aluminum distribution. These results confirmed spheres filling with the alanate. While these needle structures are not usual for sodium alanate. it is speculated that the porous silica could have provided a nucleation surface for these unique structures formation. Nevertheless, since the samples were exposed to ambient air prior to the... 

MAS) method (to record 29 Si signals) provides complementary information on the chemical bonding (Si-O-Si bond angles), aluminum distribution in the silica framework and secondary phases. 

The distribution of aluminum following intravenous, subcutaneous, intraperitoneal, and intramuscular exposure has been evaluated in studies with experimental animals (Cranmer et al. 1986 Du Val et al. 1986 Flarend et al. 1997 Leblondel and Allain 1980 Yokel and McNamara 1985, 1989). Results of these animal studies indicate that aluminum distributes to a number of tissues, organs, and biological fluids (Du Val et al. 1986 Leblondel and Allain 1980 Yokel and McNamara 1989). 

Anghileri LJ, Maincent P, Thouvenot P. 1994. Long-term oral administration of aluminum in mice. Aluminum distribution in tissues and effects on calcium metabolism. Ann Clin Lab Sci 24 22-26. 

Gomez M, Esparaza JL, Domingo JL, et al. 1998. Aluminum distribution and excretion A comparative study of a number of chelating agents in rats. Pharmacol Toxicol 82 295-300. 

Yokel RA, Lidums V, McNamara PJ, et al. 1991. Aluminum distribution into brain and liver of rats and rabbits following intravenous aluminum lactate or citrate A microdialysis study. Toxicol Appl Pharmacol 107 153-163. 

Calcium channels are suggested to mediate intestinal aluminum absorption [84]. Aluminum distributes unequally to all tissues. The values given for the aluminum levels in the human body vary widely. Under normal conditions the aluminum concentration in blood is 5-10 pmol L-1 [14, 85]. The mean aluminum concentration in human milk was 23.4 9.6 pg L-1 and did not differ significantly between colostrum, intermediate-stage, and mature-stage milk [86]. 

Figure 2. Aluminum distribution in the lower part of the lithologic sequence including underclay, the Kinneman Creek lignite, and directly overlying clay and mudstone.

The main result of extensive simulations of A1 placement in the FAU-framework topology is that random insertion of A1 into the structure, subject to Loewenstein s rule and to a weaker second neighbor Al-Al repulsion term, does not reproduce the measured Si-nAl distribution patterns [4]. The details of the aluminum distributions are therefore determined by additional or different factors. This is consistent with Melchior s model of FAU-framework construction from pre-formed 6-iing units [47,48], The simulation results also highlight the likely limitations of quantum mechanical studies of aluminum T-site preferences. If the factors controlling the aluminum distributions in zeolites X and Y are also at work in other systems, purely energetic arguments will likely have limited direct relevance for application to real materials. 

Fig. 4 Typical Aluminum Distribution in 200 p ZSM-5 Crystal from a sample with Si/Al Ratio of 62.

Fig. 5 Aluminum Distribution in ZSM-5 Crystals Synthesized (a) Template Free (b) with TPA.

C. They suggest this implicates a substi-mtion of Al -f H for Si", and argue that examining the aluminum distribution between octahedral and tetrahedral sites in mantle-derived pyroxenes would allow estimation of original water contents even for samples that have lost hydrogen during ascent. 

Molecular dynamics calculations were carried out for Na-Y zeolite with Si/Al ratio of 2.43. Different possible aluminum distributions were considered and their lattice energy values were computed based on simple force-field described in ref 20. It was possible to derive the exact distribution of aluminum, which satisfy the locations of extra framework Na ... 

Wang, Q. L., Torrealba,M.,Giarmetto,G., Guisnet,M.,Perot, G., Cahoreau, M., and Casso, J. 1990. Dealumination of Y zeolite with ammonium hexa-fluorosilicate A SIMS-XPS study of the aluminum distribution. Zeolites 10 703-706. 

Figure 7. EDX line scan analysis of a metallocene/MAO-supported silica gel regarding the silicon and aluminum distribution in the volume.

Figure 9. (a) TEM micrograph of a supported metallocene/ MAO catalyst particle prepared by gas-phase Impregnation with TMA/H2O. (b) EDX line scan analysis of the metal-locene/MAO-supported silica gel regarding the silicon and aluminum distribution in the volume. Under this condition, the active sites are formed on the outer surface of the particle. The mean particle size shifted from 50 /rm for the silica support to 70 /nm for the catalyst. 

Good PF Perl DP. (1988). A lasar microprobe mass analysis study of aluminum distribution in the cerebral cortex of dialysis encephalopathy. J Neuropathol Exp Neurol 47, 321. 

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