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 u sing an oligomeric solution aged at 368 K and conducting the intercala tion reaction, first at reflux and then with hydrothermal treatment, i n the presence of F-. Different intercalation compounds were prepared by varying the Al3+/phosphate ratio, but a unique single phase materia l with basal spacing of 21.3 Angstrom was obtained. As revealed by che mical analysis and X-ray photoelectron spectroscopy (XPS), F- is incor porated into the intercalated oligomer where it partially substitutes OH- ions. The XPS technique was also a helpful tool to determine the A l3+ concentration from which other Al3+ compounds are precipitated out side of the phosphate interlayer. Thermal treatment caused a continuou s and gradual interlayer contraction up to 973 K, but no evidence of l ayer 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 investi gate 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 spe ctra 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 o f this signal was observed upon calcination of the materials at 673 K. The presence of F- in the interlayer aluminum oxide produced an enhan cement 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 c atalyze the dehydration reaction of isopropyl alcohol with a selectivi ty of practically 100%.