Deactivation of hydrodechlorination catalysts I. Experiments with 1.1.1-trichloroethane

In order to understand the cause(s) of catalyst deactivation, microreactor studies were carried out on the catalytic hydrodechlorination (HDC) of 1,1, 1-trichloroethane (111-TCA) using a fixed-bed reactor divided into three se gments. The catalysts studied were: eta delta -alumina, alpha -alumina, Pt/ alpha -alumina, Pt/eta -alumina, and Pt/eta delta -alumina. Experiments wer e carried out at atmospheric pressure over a temperature range of 423-623 K and at H-2/111-TCA molar ratios between 10 and 99. Only the Pt-containing catalysts were able to remove all three Cl atoms from 111-TCA. However, inc reasing amounts of partially-dechlorinated compounds were formed as the Pt/ eta delta -alumina and the Pt/eta -alumina catalysts deactivated. The only product with eta delta -alumina was 1.1-dichloroethylene (11-DCE). The conv ersion of 111-TCA decreased more rapidly with time for Pt/eta delta -alumin a than for eta delta -alumina without Pt. Much larger quantities of coke we re formed on the Pt/eta delta -alumina than on the eta delta -alumina, at s imilar conditions. The eta delta -alumina was essentially completely regene rated by heating in flowing He at 773 K. The Pt/eta -alumina was only parti ally regenerated by this technique. The apparent stability of the Pt/eta de lta -alumina catalysts increased with increasing Pt concentration. Poisonin g by hydrochloric acid, a reaction product, did not cause significant deact ivation of either the eta delta -alumina or the Pt/eta delta -alumina catal ysts. (C) 2001 Elsevier Science B.V. All rights reserved.