Acid-Base Properties of the ZnO-TiO₂ Binary System

Abstract

ZnO-TiO₂ containing no sulfate ion was prepared by a coprecipitation method. Samples were calcined at 550°C in air before theiruse. The amounts of chemisorption of pyridine and CO, were measured by a gravimetric technique using a quartz balance, and the amounts ob tained were taken as the amount of acid or base.
The formations of ZnTiO₃, Zn₂Ti₃O₈ and Zn₂TiO₄ were observed by X-ray diffraction analysis. However, a part of ZnO and TiO₂ in the mixtures was considered to be amorphous. On the basis of these results, the composition of the ZnO-TiO₂ binary system was estimated (Fig.2). The BET surface area of ZnO-TiO₂ (molar ratio, 50: 50) was larger than those of ZnO and TiO₂ (Fig.3). The amounts of acid and base per unit surface area showed maxima at ZnO-TiO₂ (85: 15) and ZnO-TiO₂ (15: 85) respectively (Figs.5 and 6). IR spectra of pyridin e and NH3 chemisorbed on TiO₂ and ZnO-TiO₂ (85: 15) indicated that the acidic sites formed by mixing were Lewis-type (Figs.7 and 8). The formation of basic sites was not observed in ZnO-TiO₂ containing sulfate ion. The conversion of O_2- to Brönsted-type acidic sites by withdrawing a proton did not occur on the surface of ZnO-TiO₂ (15: 85). The formations of acidic and basic sites were explained on the basis of the hypothesis proposed by Tanabe et al.