Adsorbed species in transition metal catalyzed transformations studied by IR spectroscopy

Kiss T., János and Pálinkó, István (1997) Adsorbed species in transition metal catalyzed transformations studied by IR spectroscopy. JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, 115 (2). pp. 297-303. ISSN 1381-1169

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Abstract

Results of IR investigations are reported on several surface reactions over Pd and Ni catalysts supported on fumed silica (Cab-O-Sil). The catalysts were of low dispersion and were studied in: (a) double-bond isomerization of methylenecyclohexane (MCH), (b) ring opening of 1,1-dimethylcyclopropane (DMCP), and (c) ring opening of DMCP in the presence of D-2. It was found that during double-bond isomerization of MCH, H-D exchange (and OH-OD exchange on the support) also took place and an appreciable amount of hydrocarbon-like species remained attached to the surface of the catalysts. When DMCP 'alone' was introduced into the system, dissociative adsorption occurred (scission of one or more C-H bonds preceded C-C bond rupture). Strongly adsorbed hydrocarbon-like residues were also formed. When a DMCP + D-2 mixture was allowed to react on the catalysts, measurements indicated adsorption of a dissociative type over Pd/CS and Ni/CS. In the presence of D-2 coking was slow, there was no sign of hydrocarbon-like residues in the IR spectra of Pd/CS, i.e., product precursors could be desorbed with the help and participation of D-2. At 473 K Ni/CS probably underwent coking, however, these hydrogen-poor carbonaceous species were not detectable by IR spectroscopy.

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