Hydrogenation and isomerization over

Hydrogenation and Isomerization over Zinc Oxide R. J. Kokes and A. L. Dent... 

Upon passing bromobenzene and hydrogen over zeolite Pt-H-beta dehydrobromination followed by hydrogenation and isomerization takes place. In this way undesired aromatic bromides can be recycled. 

Finally we mention that aromatic bromides can be debrominated by hydrogen and a metal(o)-in-zeoite system (ref. 33). Over e.g. Cu(0)-Y bromobenzene is converted into benzene whereas over Pt-H-beta (200 °C) quantitative hydrodebromination is followed by hydrogenation and isomerization towards methylcyclopentane (Fig. 12). In this way undesired aromatic bromides can be recycled. 

Kokes and Dent by combining IR spectroscopy with hydrogen isotope techniques, and by applying kinetic and stereochemical considerations were able to determine the intermediate surface species in the hydrogenation and isomerization of simple olefins over zinc oxide. 

By 1992 Schuster and Platz could write Scheme 1, which economically explained much of the photochemistry of phenyl azide. UV photolysis of PA produces singlet phenylnitrene and molecular nitrogen. In the gas phase, PN is born with excess vibrational energy and isomerizes over a barrier of >30kcal/mol to form cyanocyclopentadiene, the global minimum on the CsHsN surface." This species is also vibrationally excited and sheds a hydrogen atom to form radical 3 (Scheme 1), the species detected in gas-phase absorption and emission measurements. ... 

Banks and Bailey 77> noted that the occurence of disproportionation, polymerization, and isomerization over similar catalysts, or simultaneously over the same catalyst, suggests a similarity of mechanism. They noted that this is not to say that one can predict a given catalyst will promote one or more of these reactions or that a given catalyst known to promote one of these reactions also will promote another. Banks and Bailey 77> proposed that the ability of the catalyst to shift hydrogen atoms is a key factor in determining the reaction course. When they contacted ethylene with a series of catalysts prepared by supporting Group VI hexacarbonyls on alumina, they obtained different products with the different hexacarbonyls (Table 10). 

Wang et al. [5] reported the dehydrogenation and isomerization of -butane on Cr-supported W03-Zr02 and, in his case, the catalytic activity decreased with reaction time by deposition of carbon. In our study, the catalyst performance for -butane conversion and the C4 products selectivity over Cr/H-SSZ-35 catalyst (Si/Al2=500) remained unchanged at 500°C for 6 h. From these findings on the catalytic activity and lifetime, H-SSZ-35 was expected to be one of the promising supports for the production of isobutene by hydrogenation and isomerization of n-butane. 

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