| Tartalmi leírás: |
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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