The application of an alumina-supported Ni catalyst for the hydrogenation of nitrobenzene to aniline

Connecting to a methodology developed for defining the relationship between catalyst morphology, adsorbate orientation/location and product distributions with Pd/Al2O3 catalysts, a commercial grade 20 wt% Ni/Al2O3 catalyst (HTC-500), is investigated for gas phase nitrobenzene hydrogenation at elevated temperatures. The morphology of Ni crystallites is assessed via infrared spectroscopy utilising CO as a probe molecule, with 5 separate CO adsorption sites identified. Nitrobenzene hydrogenation data is presented for a 15-hour catalyst conditioning phase, during which nitrobenzene hydrogenation was monitored at 60 °C, and at elevated temperatures post-conditioning: 100, 140, 180 and 200 °C. Nitrobenzene conversion declined with time on stream during the conditioning phase and was only recovered with reaction temperatures ≥ 180 °C. Aniline selectivity seemingly exceeded 100 % for reaction temperatures ≥ 100 °C; consideration of the associated mass balance profile for the 35-hour experiment indicated that elevating the reaction temperature facilitated the desorption of aniline, retained from the moderate temperature conditioning phase, from the catalyst. These outcomes outline the impact of temperature on nitrobenzene hydrogenation with HTC-500 and highlight the intricate competitive adsorption phenomena between reagents and products during reaction over this catalyst.