The industrial scale heterogeneously catalysed hydrogenation of nitrobenzene to produce aniline is ideally suited to the incorporation of heat recovery strategies. This presentation examines by-product formation at elevated reaction temperatures over a low loading alumina supported Pd catalyst (0.3wt%) selected for this task. The infrared spectrum of CO as a probe molecule is used to evaluate Pd crystallite morphology, which is then correlated with the observed product distributions. Vapour phase catalyst testing demonstrated near complete nitrobenzene conversion. Over-hydrogenation of aniline is identified as the dominant source of reduced product yields. In addition, formation of cyclohexanone oxime is also observed, which is linked to a separate by-product pathway involving a nitrobenzene derived hydrogenation intermediate. A nitrobenzene hydrogenation scheme is presented to account for these observations that correspond to a defined Pd crystallite morphology.

Application of alumina supported Pd catalysts for nitrobenzene hydrogenation to aniline: Morphological and mechanistic insight

ACS Spring 2022

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