Oxidation and reduction effects of propane–oxygen on Pd–chlorine/alumina catalysts |
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Authors: | M Schmal DAG Aranda FB Noronha AL Guimarães RS Monteiro |
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Affiliation: | 1. Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, PO Box 107, Yusong, Taejon, 305‐343, Korea 2. Department of Chemical Engineering, Chungbuk National University, Cheongju, Chungbuk, 361‐763, Korea
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Abstract: | Pd–chloride precursor salt was used to prepare Pd/Al2O3 catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess
of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was
related to the Pd2+ sites observed on Pd/Al2O3 through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H2, the IR spectra showed the linear and bridge adsorbed CO species on the Pd0 surface. After propane reaction, a new band at 2130 cm-1 related to CO adsorption on Pd2+ species was noted. Carbon monoxide species adsorbed on Pd0 were also observed in all samples after reaction. Our results suggest surface ratios of Pd0/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were
affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction
helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However,
the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane
oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible
formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations
into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After
water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition.
This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water
and the reaction temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | oxidation reduction of palladium catalysts chlorine effects |
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