Pretreatment Effect on Pt/CeO2 Catalyst in the Selective Hydrodechlorination of Trichloroethylene

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• 作者：Noelia Barrabs ; Karin Fttinger ; Jordi Llorca ; Anton Dafinov ; Francesc Medina ; Jacinto S ; Christopher Hardacre ; Gnther Rupprechter
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：October 21, 2010
• 年：2010
• 卷：114
• 期：41
• 页码：17675-17682
• 全文大小：335K
• 年卷期：v.114,no.41(October 21, 2010)
• ISSN：1932-7455

文摘

Pt−ceria catalysts present different surface chemistries depending on the preparation method and the pretreatment. The catalytic behavior of Pt/CeO₂ catalysts in the hydrodechlorination of trichloroethylene (TCE) to ethylene was examined as a function of the pretreatment conditions and the noble metal precursor salts. Using FTIR and X-ray photoelectron spectroscopy, significant differences were observed in the surface properties of Pt/CeO₂ prepared from the H₂PtCl₆ precursor after different pretreatment procedures (i.e., reduction or oxidation−reduction). These surface changes are related to chloride residues from the synthesis. Strong changes were observed in the selectivity of the catalysts to ethylene depending on the pretreatment conditions. The 0.5%Pt/CeO₂ catalyst showed a 13% selectivity toward ethylene after reduction, whereas after oxidation, followed by reduction, the selectivity increased up to 85% at the same conversion level. This effect was only observed when a chloride-containing precursor was used in the preparation. In this way, it is demonstrated that the use of a Cl-containing Pt precursor and an air treatment prior to reduction strongly improves the ethylene selectivity of Pt−CeO₂ dechlorination catalysts. This can be explained by formation of a CeOCl phase during the synthesis that decomposes upon air tempering, producing oxygen vacancies on the ceria support. We propose that these oxygen vacancies are active for cleaving off Cl from the TCE. Pt then supplies H to clean-off Cl as HCl. Reaction of TCE on Pt produces rather ethane, so Pt may be partly Cl-poisoned for the hydrodechlorination reaction but not for H₂ dissociation or CO adsorption.