GENERATION OF ACID SITES ON TIO2-SNO2 BINARY OXIDE PREPARED FROM METAL ALKOXIDES

In order to reveal the origin of acid sites generated on TiO2-SnO2 binary oxide, the influences of Ti-O-Sn bonds formed in the binary oxide and of the particle size of the component metal oxides on acid properties were studied. The binary oxides were prepared by two different methods; one is simultaneous hydrolysis of Ti and Sn mixed alkoxide solution and the other is physical mixing of two oxides which were separately prepared by hydrolysis of Ti and Sn alkoxides. These powdered samples were calcined at 420-degrees-C in air. The formation of solid solution between TiO2 and SnO2, suggesting the presence of Ti-O-Sn bonds, was observed by x-ray diffraction and Raman spectroscopy on the co-precipitated oxide, but was never observed in the physically mixed oxide. Strong acid sites (H-0 = -3.0) were observed on both the binary oxides. This suggests that the presence of Ti-O-Sn bonds will not affect upon the acid properties of the binary oxide system. On the other hand, titration tests and NH3-TPD measurements showed that the acid strength increased with a decrease in the particle size of TiO2 and SnO2 single oxides themselves. We concluded that the formation of small sized particles in TiO2, SnO2 and the binary oxide makes an important contribution to the generation of strong acid sites.