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Aqueous-Phase Hydrodechlorination of Trichloroethylene over Pd-Based Swellable Organically Modified Silica: Catalyst Deactivation Due to Sulfur Species

2019-03-13
Çelik, Gökhan
Ailawar, Saurabh A.
Gunduz, Seval
Miller, Jeffrey T.
Edmiston, Paul L.
Ozkan, Umit S.
One of the problems of catalytic water treatment systems is that sulfur-containing species present in contaminated water have a detrimental effect on the catalytic performance because of strong interactions of sulfur species with active metal sites. In order to address these problems, our research has focused on developing a poison-resistant catalytic system by using a novel material, namely, swellable organically modified silica (SOMS), as a catalyst scaffold. Our previous investigations demonstrated that the developed system was resistant to chloride poisoning, active metal leaching, and carbon deposition under reaction conditions. This study examines the sulfur tolerance of the developed catalytic system for hydrodechlorination (HDC) of trichloroethylene (TCE) by subjecting Pd-incorporated samples to different sulfur species, including sulfates (SO42–), bisulfides (HS–), and hydrogen sulfide (H2S). The pristine and sulfur-treated catalysts were then tested for aqueous- and gas-phase HDC of TCE and characterized by several techniques, including N2 physisorption, X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS), and temperature-programmed reaction (TPrxn) with H2. The investigations were also performed on Pd/Al2O3, a commercially used HDC catalyst, to have a basis for comparison. The activity and characterization results revealed that Pd/Al2O3 underwent deactivation due to exposure to sulfur-containing compounds. Pd/SOMS, however, exhibited better resistance to aqueous sulfates, bisulfides, and gas-phase H2S. In addition, the removal of sulfur species from completely poisoned catalysts was found to be more facile in Pd/SOMS than Pd/Al2O3. The tolerance of Pd/SOMS to sulfur poisoning was attributed to stem from the novel characteristics of SOMS, such as swelling ability and extreme hydrophobicity.