FOURIER-TRANSFORM LASER RAMAN-SPECTROSCOPY OF ADSORBED PYRIDINE AND NATURE OF ACID SITES ON CALCINED PHOSPHATE ZR(OH)(4)

Two phosphated zirconias were prepared by calcination at 600 degrees C of (NH4)(2)HPO4-impregnated zirconium hydroxide [Zr(OH)(4)] and monoc linic zirconia (m-ZrO2). X-ray powder diffractometry, infrared spectro scopy and laser Raman spectroscopy showed the calcination product of t he former precursor [(NH4)(2)HPO4/Zr(OH)(4)] to assume a bulk structur e consisting of face-centred cubic zirconia (c-ZrO2), and exhibit larg e surfaces (102 m(2)/g) enriched with pyrophosphate-like polymeric spe cies. In contrast, the calcination product of the latter precursor [(N H4)(2)HPO4/mZrO(2)] was found to retain the bulk structure of the oxid e (m-ZrO2), and expose moderate surfaces (33 m(2)/g) enriched with ort hophosphate-like monomeric species. Raman spectroscopy of adsorbed pyr idine probed on the phosphated c-ZrO2 hydrogen-bond donor (ZrOH), Lewi s (coordinatively unsaturated Zr4+) and Bronsted (POH) acid sites. On the phosphated m-ZrO2, hydrogen-bond donor and Lewis acid sites were d etectable, whereas Bronsted acid sites were not. It is concluded that the generation of Bronsted acid sites on phosphated zirconia necessita tes the employment of Zr(OH)(4) as a precursor compound for the zircon ia. (C) 1998 Elsevier Science B.V. All rights reserved.