The application of alumina supported Pd catalysts for high selectivity aniline synthesis catalysis at elevated temperatures: Site-selective chemistry

Abstract

The industrial scale heterogeneously catalysed hydrogenation of nitrobenzene to produce aniline is ideally suited to the incorporation of heat recovery strategies. However, a range of by-products may be observed. Thus, discerning the origins of by-product formation is crucial for developing targeted prototype catalysts. This paper examines by-product formation at elevated reaction temperatures over a previously untested low loading alumina-supported Pd (0.3 wt%) industrial grade prototype aniline synthesis catalyst in the vapour and liquid phase. Infrared spectroscopy of chemisorbed CO is used to evaluate the Pd crystallite morphology. Importantly, the morphology is seen to differ from other previously analysed 0.3 wt% Pd/Al2O3 catalyst samples. Post-reaction (vapour phase) analysis of the catalyst identifies carbon laydown to preferentially neutralise Pd(100) sites. An inter-relationship is proposed via observed nitrobenzene hydrogenation chemistry and crystallite morphology, such that specific reactions are associated with specific planes of the Pd crystallites of this Pd/Al2O3 catalyst.