Nature of Acid Sites on TiO2, and Their Reactions with OH and NH2 Groups of 3-Amino-1-propanol, 1-Propanol, and 1-Propylamine

Abstract

The IR spectra for pyridine adsorbed on the surfaces of TiO2 (SA) (anatase type), prepared from titanium tetraisopropoxide, showed the existence of only Lewis acid sites which were not converted to the Br\ddotonsted type by the addition of water. However, TiO2 (SB) (anatase type), prepared by the hydrolysis of titanium oxide sulfate, showed both Lewis and Br\ddotonsted acidities. The Lewis acidity of SB was converted to the Br\ddotonsted type by the introduction of water vapor. The 3-amino-1-propanol compound interacted with both Lewis and Br\ddotonsted acid sites on the TiO2 surfaces in a manner similar to propylamine rather than to 1-propanol. However, in the case of SA, interactions between OH groups of the amino alcohol and surface OH groups seemed to take place to some extent. The mode of the surface reaction of TiO2 differes markedly from that of SiO2 which has no surface acidity. A linear relationship between the amount of surface OH groups on SB and the amount of the reaction of 3-amino-1-propanol at 235 °C in an autoclave was observed. The formation of oriented and closely packed layers of adsorbed molecules was observed for all the combination of SB and 3-amino-1-propanol, in which some condensation (mainly dimerization) seemed to be promoted by acid sites on SB.