Metal complexes of phthalocyanine and $alpha;,$beta;,$gamma;,$delta;-tetraphenyl porphyrin as heterogeneous catalysts in oxidative dehydrogenation. Correlation between catalytic activity and redox potential
1970; Elsevier BV; Volume: 17; Issue: 1 Linguagem: Inglês
10.1016/0021-9517(70)90076-x
ISSN1090-2694
Autores Tópico(s)Oxidative Organic Chemistry Reactions
ResumoAbstract The catalytic activity of tetraphenyl porphyrin and phthalocyanine complexes for the heterogeneous dehydrogenation of cyclohexadiene in the gas phase, using nitro-benzene as the oxidizing agent, was measured. A general correlation of catalytic activity with polarographically measured first oxidation potentials was found. By controlled potential electrolysis, coulometry and EPR measurements, the mode of oxidation of these complexes in solution was ascertained. The first oxidation of Fe 2+ and Co 2+ tetraphenyl porphyrin appeared to be at the central metal atom, while the Zn 2+ and Cu 2+ complexes gave ligand oxidation. For the Ni 2+ complex the potentials for central metal atom oxidation and ligand oxidation were very close together. Therefore, these complexes were capable of two kinds of redox processes, either valency change of the central metal atom (Fe 2+ , Co 2+ ) or ligand oxidation/reduction (Cu 2+ , Zn 2+ ) or both (Ni 2+ ). By comparing these principles with results obtained earlier on the catalytic activity of these complexes for cumene oxidation, this difference in redox mechanism could be correlated with the catalytic activity of the complexes in question.
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