Gas-phase hydration of ethene over tungstena–zirconia

Abstract

Hydration of ethene over a variety of tungstena–zirconia (WO 3/ZrO 2) catalysts of different W/Zr ratios using different calcination temperatures is studied at 473 K using a continuous fixed-bed reactor at atmospheric pressure. The maximum activity for ethene hydration is obtained by calcination at 1073 K with a W/Zr ratio of 0.4, while skeletal isomerization of n-butane is found to exhibit a maximum rate at W/Zr=0.1. The most active WO 3/ZrO 2 catalysts is demonstrated to be superior in activity to other typical solid acids such as H 4SiW 12O 40/SiO 2, zeolites (H-ZSM-5 and H-β), various mixed oxides, and polymer resins. Lifetime tests reveal that constant activity of WO 3/ZrO 2 obtained at 72 h is about 70% of initial activity and that the activity is largely recovered by calcination at 773 K in air. The specific activity (per surface area) of WO 3/ZrO 2 is correlated with the hydrophobicity as estimated from the adsorption of water rather than with that estimated from the density of acid sites measured by NH 3-TPD. Therefore, the pronounced activity of WO 3/ZrO 2 is mainly brought about by the high hydrophobicity of the surface along with the inherent acidity.