Surface acidity of the layered pyrophosphates of quadrivalent Ti, Zr, Ge, and Sn and their activity in some acid-catalysed reactions

Abstract

The layered pyrophosphates of quadrivalent Ti, Zr, Ge, and Sn have been prepared and characterized by Fourier-transform i.r. spectroscopy, differential thermal analysis, thermogravimetry, X-ray diffraction, and surface area measurements. Their surface acidity has been investigated by Fourier-transform i.r. spectroscopy, with an analysis of the OH stretching region and of the spectra of adsorbed basic molecules (pyridine and acetonitrile), as well as by measuring their activity in acid-catalyzed reactions. The trend of the surface Bronsted-acid strengths found was Ge > Sn Ti > Zr, corresponding to the trend in electronegativity of the elements, while the opposite trend was found for the surface Lewis-acid strengths.