화학공학소재연구정보센터
Journal of Physical Chemistry, Vol.100, No.35, 14726-14735, 1996
Preparation and Properties of Fluorinated Alumina-Pillared Alpha-Zirconium Phosphate Materials
A polyoxyaluminum cluster, larger than the tridecamer ion [AlO4Al12(OH)(24)(H2O)(12)](7+), was intercalated into alpha-zirconium phosphate using an oligomeric solution aged at 368 K and conducting the intercalation reaction, first at reflux and then with hydrothermal treatment, in the presence of F-. Different intercalation compounds were prepared by varying the Al3+/phosphate ratio, but a unique single phase material with basal spacing of 21.3 Angstrom was obtained. As revealed by chemical analysis and X-ray photoelectron spectroscopy (XPS), F- is incorporated into the intercalated oligomer where it partially substitutes OH- ions. The XPS technique was also a helpful tool to determine the Al3+ concentration from which other Al3+ compounds are precipitated outside of the phosphate interlayer. Thermal treatment caused a continuous and gradual interlayer contraction up to 973 K, but no evidence of layer collapse or segregation of alumina was found, at least up to 1273 K. P-31 and Al-27 solid state NMR spectroscopies were used to investigate the mechanism of interaction between the phosphate layer and the aluminum species. Because of this interaction, the P-31 signal shifts toward higher field, at approximate to 20 ppm, while the Al-27 NMR spectra display the characteristic signal of octahedrally coordinated Al and of a new resonance between 44.8 and 49.8 ppm, which is related to the existence of Al-O-P bonds. An increase of the relative intensity of this signal was observed upon calcination of the materials at 673 K. The presence of F- in the interlayer aluminum oxide produced an enhancement of the thermal stability and porosity of the pillared materials. Studies of thermal-programmed desorption of NH3, pyridine adsorption, and decomposition of isopropyl alcohol have revealed the acid nature of fluorinated alumina-pillared alpha-ZrP materials. The acid sites catalyze the dehydration reaction of isopropyl alcohol with a selectivity of practically 100%.