Deactivation of hydrodechlorination catalysts: I. Experiments with 1,1,1-trichloroethane Original Research Article

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 segments. The catalysts studied were: ηδ-alumina, α-alumina, Pt/α-alumina, Pt/η-alumina, and Pt/ηδ-alumina. Experiments were carried out at atmospheric pressure over a temperature range of 423–623 K and at H2/111-TCA molar ratios between 10 and 99. Only the Pt-containing catalysts were able to remove all three Cl atoms from 111-TCA. However, increasing amounts of partially-dechlorinated compounds were formed as the Pt/ηδ-alumina and the Pt/η-alumina catalysts deactivated. The only product with ηδ-alumina was 1,1-dichloroethylene (11-DCE). The conversion of 111-TCA decreased more rapidly with time for Pt/ηδ-alumina than for ηδ-alumina without Pt. Much larger quantities of coke were formed on the Pt/ηδ-alumina than on the ηδ-alumina, at similar conditions. The ηδ-alumina was essentially completely regenerated by heating in flowing He at 773 K. The Pt/η-alumina was only partially regenerated by this technique. The apparent stability of the Pt/ηδ-alumina catalysts increased with increasing Pt concentration. Poisoning by hydrochloric acid, a reaction product, did not cause significant deactivation of either the ηδ-alumina or the Pt/ηδ-alumina catalysts.