Mechanistic Insight Into the Application of Alumina-Supported Pd Catalysts for the Hydrogenation of Nitrobenzene to Aniline

Two Pd/gamma-Al2O3 catalysts are examined for the vapor phase hydrogenation of nitrobenzene over the temperature range of 60-200 degrees C. A 1 wt % catalyst is selected as a reference material that is diluted with gamma-alumina to produce a 0.3 wt % sample, which is representative of a metal loading linked to a candidate industrial specification aniline synthesis catalyst. Cyclohexanone oxime is identified as a by-product that is associated with copy and temperature-programed desorption measurements of chemisorbed CO provide information on the morphology of the crystallites of the higher Pd loading catalyst. The lower Pd loading sample exhibits a higher aniline selectivity by virtue of minimization of product overhydrogenation. Reaction testing measurements that were undertaken employing elevated hydrogen flow rates lead to the proposition of separate reagent and product-derived by-product formation pathways, each of which occurs in a consecutive manner. A global reaction scheme is proposed that defines the by-product distribution accessible by the grades of catalyst examined. This information is helpful in defining product purification procedures that would be required in certain heat recovery scenarios connected with large-scale aniline production.

Automated summary

Two Pd/gamma-Al2O3 catalysts were studied for the vapor phase hydrogenation of nitrobenzene. It was found that the catalyst with higher metal loading exhibited higher selectivity towards aniline, while the catalyst with lower metal loading minimized product overhydrogenation. A global reaction scheme was proposed based on the experimental results to define the accessible by-product distribution of the examined catalysts. This is important for defining the product purification procedures required in heat recovery scenarios connected with large-scale aniline production.