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n-Pentane and 3-Methylpentane Conversions on Differently Pretreated Supported Palladium Catalysts

Bonarowska M., Karpiński Z.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 11

1877-1887

EN

Metal-support interactions in silica- and alumina-supported palladium catalysts have been investigated by using n-pentane and 3-methylpentane conversions as test reactions. High temperature reduction (HTR) at 600 graduate C results in a considerable increase of the selectivity towards isomeric and cyclic products, i.e. causes a similar effect as in the case of previously studied reactions of 2,2-dimethylpropane and various C6-alkanes. However, the silica-supported palladium catalysts behave differently from the Pd/Al2O3. For the former catalysts subjected to HTR, the selectivity for cyclic products is enhanced, whereas a similarly pretreated Pd/Al2O3 gives mainly isomers. This observation, and the changes in both the hydrogen reaction order and in the activation energy caused by different catalyst pretreatment, were both analyzed in detail. All mentioned quantities appeared to be new convenient diagnostic parameters towards determining whether or not palladium interacts with a support.

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n-Butane Conversion on Differently Pretreated Supported Palladium Catalysts

Bonarowska M., Karpiński Z.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 11

1821-1828

EN

Metal-support interactions in silica- and alumina-supported palladium cata lysts have been re-investigated by using n-bu tane converion as a test reaction. High temperature reduction at 600°C results in a consider able in crease in the isomerization selectivity, i.e. a similar effect as in the case of previously studied rea tions of 2,2-dimethylpropane and C6-alkanes. There fore, changes in the selectivity for isomerization and also in the activation energy can be re garded as use ful diagnostic parameters to wards determining whether or not palladium interacts with a support.

3

Hydrodechlorinationo of Dichloridifluoromethane (CFC-12) on Silica-Supported Palladium and Palladium-Gold Catalysts

Malinowski A.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 10

1461-1466

EN

Silica-supported palladium and palladium-gold catalysts were screened in the reaction of dichlorodifluoromethane with dihydrogen at 180_C. The Au-containing sample appeared superior as far as the selectivity towards difluoromethane (desired reaction product) is concerned (95% vs. ~30% for Pd/SiO2). A comparative X-ray diffraction study of the catalysts, before and after reaction, confirmed our earlier findings that during the hydrodechlorination massive amounts of carbon originated from CCl2F2 dissolve in palladium. However, a similar conclusion cannot be drawn from XRD studies of the Pd-Au/SiO2 catalyst, because upon entering Pd bulk both gold and carbon may produce analogous shifts of the XRD reflections. For that reason, temperature programmed hydrogenation of carbon deposited in the Pd and a Pd-Au catalyst was used. In contrast to the behaviour of monometallic Pd/SiO2, only insignificant quantity of carbon was found in the bimetallic Pd-Au/SiO2 sample subjected to hydrodechlorination. This result supports the idea that a complete hydrodehalogenation of CCl2F2 to methane would occur via bare carbon adspecies. Thus, one can associate a superior catalytic behaviour of Pd-Au alloy catalysts (selectivity to CH2F2 ~95%) with a low abundance of C1 adspecies.