Calorimetric study of the kinetics of adsorption of hydrogen loaded titanium oxide

Abstract

The thermol~inetics of the adsorption of hydrogen on a loaded titanium dioxide has been studied by microcalorimetry.A diffusion process in the open structure of the oxide seems to be the rat6r determim'ng step. Some exceptions at the rule of the S-shaped z-t plot were found.The function "z" is here obtained from the thermokinetics of the process and is constituted by the reciprocal of the time derivative of the fraction of the integra~ heat of adsorption, i.e., by the reciprocal of the relative heat flow.A review of empirical isotherms and of theoretical models proposed for the kinetics of adsorption has been recently published [1]. One conclusion of this paper is that the plot of the reciprocal of the rate of adsorption against time is convex at small "t" and concave at large "t" and the region of constant rate sometimes proceeds the convex region.The present article which deals with the adsorption of hydrogen on a doped titanium dioxide attempts to show that some exceptions to this rule may occur. ExperimentalThe material studied was a titania-based catalyst that is proposed for the production of hydrogen by the photocleavage of water [2]. A sample of TiO2 from Degussa (P-25, surface area 55 mZ/g; 72% anatase, 28% rutile) was loadedJohn Wiley & Sons, Limited, Chichester Akad~niai Kiad6, Budapest