The flow hydrogenation of benzene vapour on silica‐supported nickel catalysts

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Abstract
The hydrogenation of benzene vapour has been studied in a flow system using a ‘practical’ nickel‐on‐silica catalyst between 40° and 275° at atmospheric pressure. The reaction rate dependence was zero‐order with respect to benzene partial pressure in the range 60—150 mm. investigated and second‐order with respect to hydrogen. The apparent activation energy changes from 2.0 ± 0.2 kcal./mol. to around 0.9 ± 0.1 kcal./mol. to −19.5 ± 0.5 kcal./mol. in three distinct temperature regions.The results are discussed in terms of a possible rate limitation and it is suggested that, above 170°, cyclohexane once formed at the surface may possibly be dehydrogenated, since the energetics are favourable. The rate‐controlling step in the mechanism may be the transfer of hydrogen molecules from a van der Waals layer to the catalyst surface where, on dissociation, these react with C6H8(ads.) to give C6H10(ads.) and finally C6H12.A brief study of catalyst poisoning by water vapour has been included.
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