Infrared study of the adsorption of water on to the surface of rutile

Abstract

Infrared spectra of the surface of three samples of rutile which had been (a) calcined in air at 723 K and heated in oxygen at 673 K, (b) calcined in air at 973 K and heated in oxygen at 673 K, and (c) calcined in air at 723 K and heated in hydrogen at 673 K have been recorded as a function of the extent of hydroxylation and hydration of the oxide surface. The adsorption and desorption characteristics of associatively adsorbed and chemisorbed water on rutile have been established in detail and are discussed primarily in terms of adsorptive interactions involving the {110}, {100} and {101} surface planes. Calcination of rutile at high temperature (973 K) enhanced the chemisorption of water on {110} planes at the expense of the associative adsorption of water on Ti⁴⁺ ion sites in the {100} and {101} planes. Mild reduction of rutile in hydrogen decreased the ability of the oxide to adsorb water molecularly. The effect of reduction was completely reversed by subsequent heat treatment of the oxide in oxygen.