Pseudo-boehmite

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Pseudoboehmite is an aluminum compound with the chemical composition AlO (OH). It consists of finely crystalline boehmite . However, the water content is higher than in boehmite.

history

Calvet et al. coined the term pseudobömit in 1952 when they synthesized a pure, synthetic aluminum hydroxide gel. The XRD spectrum is similar to that of boehmite but with different relative intensity of the peaks.

morphology

Pseudoboehmite consists essentially of finely crystalline boehmite, which consists of the same or similar octahedral layers in the xz plane , but does not have a three-dimensional structure, since there are only a few unit cells in the y direction. It consists of a considerable number of crystallites with a single unit cell in the y-direction or individual octahedral layers. It contains more water, which is usually found between the octahedral layers, usually arranged randomly but sometimes regularly.

The water content consists of adsorbed and chemically bound water. The higher water content compared to boehmite can be explained by the smaller crystallites. While boehmite consists of relatively long AlOOH chains that end with H 2 O, these chains are much shorter in pseudo boehmite. The relative water content is significantly increased by the terminal water molecules:

Pseudoboehmite structure.gif

It is an "only slightly crystallized" Al 3+ compound with the composition Al 2 O 3  * x H 2 O (1.0 <x <2.0) with increased interplanar distances of 0.67 nm in the [020] direction in comparison to 0.612 nm for boehmite .

At higher temperatures, pseudoboehmite converts to γ-aluminum oxide, with the size distribution of the pores being maintained up to 1000 ° C. At 1100 ° C, however, sintering already takes place and the specific surface area decreases because a transition to α-Al 2 O 3 takes place.

Manufacturing

It is obtained by aging aluminum hydroxide gel at a pH of 5.0 to 7.4.

use

Pseudoboehmite is used as a binder in the manufacture of FCC catalysts and adsorbents . It can also be used as a raw material for the production of activated alumina. A broad application is the production of γ-Al 2 O 3. Due to its low cost, high thermal stability and specific surface, it is used for the production of sorbents, catalysts and catalyst carriers. Pseudoboehmite is also used for the production of α-Al 2 O 3 , which is used as a refractory material , insulating and abrasion protection agent .

Individual evidence

  1. ↑ Calvet, E., Bovinet, P., Noel, M., Thibon, H., Maillard, A., Tertian, R .; Contribution a l'étude des gels d'alumine , Bulletin de la Société Chimique de France, 1952, (19), 99-108
  2. ↑ de Souza Santos, P., Viera Coelho, AC, de Souza Santos, H., Kunihiko Kiyohara, P .; Hydrothermal Synthesis of Well-Crysatllized Bohemite Crystals of Various Shapes , Materials Research, Vol. 12, No. 4, (2009), 437-445
  3. ↑ Tettenhorst, R., Hofmann, DA; Crystal Chemistry of Boehmite , Clays and Clay Minerals, Vol. 28, No. 5, 373-380, (1980)
  4. ↑ Baker, BR, Pearson, RM; Water Content of Pseudoboehmite: A New Model for its Structure , Journal of Catalysis, 33, 265-278 (1974)
  5. ↑ a b Vieira Coelho, AC et al., Specific Surface Area and Structures of Aluminas from Fibrillar Pseudoboehmite , Revista Matéria, 13, 2 (2008), pp. 329-341
  6. ↑ Nogi, K., Naito, M., Yokoyama, T .; Nanoparticle Technology Handbook, p. 204
  7. ↑ Cai, W., Li, H., Zhang, Y .; A New Route for H 2 O 2 -Precipitated Pseudoboehmite from Sodium Aluminate Solutions with High Na 2 O / Al 2 O 3 Molar Ratio , Chinese Academy of Sciences, Beijing, China