AL MODIFIED SEPIOLITE AS CATALYST OR CATALYST SUPPORT

Fibrous mineral sepiolite is formed of staggered talc sheets. The discontinuous octahedral layers provide for infinite channels along the fiber axis with cross-section approximately (10 x 4) angstrom2. During crystal growth, a second set of irregularly shaped pores with a diameter around 100 angstrom is created within the fiber. Zeolitic water fills the narrow and regular channels and is eliminated by outgassing at 100-degrees-C. At that stage, the specific surface area is approximately 300 M2/g. Upon activation at increasing temperature, the structure folds, and ultimately collapses (approximately 500-degrees-C), leaving a surface area approximately 150 m2/g. The natural mineral lattice is almost neutral, having a cation-exchange capacity (CEC) in the order of 0.07 meq.g-1. It is shown that mild treatment with NaAlO2 results in partial Si-by-Al substitution in the tetrahedral layer. The CEC is almost tripled, and the residual surface area after calcination is about the same as in the original material. The alumination process generated Lewis sites evidenced by pyridine adsorption study. The mechanism of alumination, as well as the structural modifications upon calcination, are discussed on the basis of Al-27 and Si-29 MAS-NMR spectroscopy. Possible uses of the Al modified sepiolite as catalyst and catalyst support are proposed.