Pseudo-liquid phase catalysis of heteropoly compound: Application of the effectiveness factor concept.

Abstract

The “pseudo-liquid phase” catalytic behavior of 12-tungstophosphoric acid was confirmed by studying the effect of catalyst particle size on the apparent rate of t-BuOH dehydration. The apparent rate of reaction strongly depended on the particle size, indicating strong diffusional effects in the pseudo-liquid phase. Based on the theory of Thiele with some modification and extension to pseudo-liquid phase catalysis, along with a knowledge of intrinsic reaction rate, diffusivity values were evaluated. The effective dilfusivity was found to lie in a range of 10–11–10–10 m2/s, which are very small values for diffusivity in gas phase, but close to that in liquid-filled pores. Due to the large temperature dependency of diffusivity, the effectiveness factor is smaller in the lower-temperature region—a sharp contrast to the usual diffusion-restricted gas–solid catalytic reaction in a microporous solid.