Washcoated Pd / Al 2 O 3 monoliths for the liquid phase 1 hydrodechlorination of dioxins

14 15 The catalytic activity and durability of 2 wt. % Pd/Al2O3 in powder and washcoated on cordierite 16 monoliths were examined for the liquid phase hydrodechlorination (LPHDC) of polychlorinated 17 dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs). NaOH was employed as a 18 neutralizing agent, and 2-propanol was used as a hydrogen donor and a solvent. Fresh and spent 19 powder and monolith samples were characterized by elemental analysis, surface area, hydrogen 20 chemisorption, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), 21 and transmission electron microscopy/energy dispersive X-ray spectroscopy (TEM/EDS). Three 22 reactor configurations were compared including the slurry and monolith batch reactors as well as 23 the bubble loop column resulting in 100, 70, and 72% sample toxicity reduction, respectively, after 24 5 h of reaction. However, the slurry and monolith batch reactors lead to catalyst sample loss via a 25 filtration process (slurry) and washcoat erosion (monolith batch), as well as rapid deactivation of 26 the powder catalyst samples. The monolith employed in the bubble loop column remained stable 27 and active after four reaction runs. Three preemptive regeneration methods were evaluated on spent 28 monolith catalyst including 2-propanol washing, oxidation/reduction, and reduction. All three 29 procedures reactivated the spent catalyst samples, but the combustion methods proved to be more 30 efficient at eliminating the more stable poisons. 31 32