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Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene

Paper ID Volume ID Publish Year Pages File Format Full-Text
48542 46512 2007 10 PDF Available
Title
Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene
Abstract

Calcined and reduced catalysts Pd/LaBO3 (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of toluene is converted): Pd/LaFeO3 > Pd/LaMnO3+δ > Pd/LaCoO3 > Pd/LaNiO3. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H2-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO3 (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO3 and either 200 or 250 °C for LaCoO3. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO3 was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B3+ (B = Mn) or B2+ even to B0 (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd0 reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd2+/Pd4+ and Pd0/Pd2+/Pd4+ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co3+ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO3 for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity.

Keywords
Palladium; Perovskite; XPS; Catalytic oxidation
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Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 75, Issues 3–4, 26 September 2007, Pages 157–166
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
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