Elaboration of an aqueous sol-gel method for the synthesis of g-Al2O3 supports

V. Claude1, C. Wolfs1 and S. D. Lambert1

1Department of Chemical Engineering – Nanomaterials, Catalysis, Electrochemistry, University of Liege, B6a, B-4000 Liege, Belgium. E-mail :

γ-Al2O3 material appears to be the best catalytic support for applications at high temperatures such as CH4 reforming, biomass gazification into Syngas,... Instead of using commercially available γ-Al2O3 materials, this work presents the synthesis of alumina supports by the sol-gel process, in order to be able to tailor the micro- and meso-structure of γ-Al2O3 supports. The cogelation (realized by organic path) and coprecipitation (realized by aqueous path) methods allow the synthesis of homogenous supports from the hydrolysis and condensation of different kind of precursors.

The cogelation syntheses can be realized with precursors being both alkoxides of the same element, for example the formation of SiO2 with tetramethoxysilane (Si(OCH3)4) and tetraethoxysilane (TEOS, Si(OC2H5)4) [1, 2]. It is also possible to start from one alkoxide and one salt, for example the synthesis of Al2O3 with a mix of Al-isopropoxide (Al(OC3H7)3)/aluminum nitrate (Al(NO3)3) [3] or Al-isopropoxide/aluminum acetylacetonate (Al(C5H7O2)3) [4]. The more interesting aspect of the cogelation lies in the possibility to create homogeneous inorganic materials with different elements. Similar materials can be obtained by coprecipitation by using a combination of TEOS and aluminum salts (Al(NO3)3, Al(Cl3)3) [5].

Cogelation with a functionalized precursor is also possible in order to tailor the morphology of the material. In this way, the use of silicon alkoxide containing a functional organic group made of one or several amino groups, which are able to form a chelate with a metallic ion, has proved to be an innovative and efficient way to improve the performances of catalytic materials. Indeed, the amino-metal complex of the functional chain allows an efficient dispersion of the metallic nanoparticles inside the inorganic support, thus improving the activity and lifetime of the catalyst. In this way, Lambertet al. [1, 2] synthesized finely dispersed Ni and Ni-Cu/SiO2 by the homogeneous cogelation of a common silicon alkoxide (TEOS) and an amino-group functionalized silicon alkoxide (N-[3-(trimethoxysilyl)propyl]ethylenediamine, (CH3O)3-Si-(CH2)3-NH-(CH2)2-NH2; called EDAS).

Since no functionalized aluminum precursors are commercially available, the functionalization of alumina supports is usually realized via grafting methods. The usual methods consist in the mixing of a functionalized silica precursor with an alumina support in an organic solvent. Thereafter, a small quantity of water is added to hydrolyze the alkoxy groups and form silanol groups which graft onto the alumina support by condensation reactions [6]. Though showing interesting results for the dispersion of metallic active sites, these methods are nevertheless not convenient and difficult to scale up, principally because of the required synthesis conditions (inert and dry atmosphere, toxic solvents such as toluene). One goal of this work was to develop an easy synthesis procedure for the cogelation between a functionalized silicon alkoxide (EDAS) and alumina hydroxide.Furthermore, the influences of the organosilane nature on the physico-chemical properties of alumina supports were realized.

References

  1. J. G. Mahy, V. Claude, L. Sacco, S. D. Lambert,Journal of Sol-Gel Science and Technology (2017) 81, 59.
  2. S. Pirard, J. Mahy, J.-P. Pirard, B. Heinrichs, L. Raskinet, S. D. Lambert,Microporous and Mesoporous Materials(2015) 209, 197.
  3. J. Delgado, M. P. Aznar, J. Corella, Industrial and Engineering Chemistry Research (1997) 36, 1535.
  4. B. Acharya, A. Dutta, P. Basu, International Journal of Hydrogen Energy (2010) 35, 1582.
  5. L. Zhang, X. Wang, B. Tan, U.S. Ozkan, Journal of Molecular Catalysis A: Chemical (2009) 297, 26.
  6. D.Y. C. Leung, X. Wu, M.K.H. Leung, Applied Energy (2010) 87, 1083.