Hydrogenation of Nitrobenzene over a Pd/Al₂O₃ Catalyst – Mechanism and Effect of the Main Operating Conditions

Abstract

The catalytic hydrogenation of nitrobenzene (NB) was studied in a three-phase basket reactor with a commercial Pd/Al 2 O 3 sample as catalyst. The kinetic experiments allowed a better understanding of the mechanism behind the formation of aniline (ANL) and by-products, a topic not yet well comprehended. The effect of some operating conditions was studied and the existence of more by-products than mentioned in the literature was stated; specifically, benzene formation was verified. Both the reaction kinetics and selectivity were found to be strongly dependent on the temperature, while the effect of total pressure is not that pronounced. Moreover, the high selectivity of the catalyst used in the present work was proved, and as such the deep hydrogenation of ANL to form by-products only occurs in considerable extension when the NB concentration in the reaction mixture becomes negligible.

Theoretical analysis of the “green” synthesis of aniline by reduction of nitrobenzene

“…Aniline (AN) is an important chemical intermediate used for instance to synthesize polyurethane (Travis, 2007), The traditional way to produce AN is to reduce nitrobenzene (NB) to AN using hydrogen over a metal catalyst can produce a 100 % selectivity towards AN at high pressure and temperature between 100 and 200°C (Couto et al, 2015), the process is particularly selective and efficient (about 67% yield) (Varkolu et al, 2016;Wisniak et al, 1984). 100 Years ago, Haber (Haber, 1898) proposed a reaction pathway (Figure 1) for the reduction of NB according to which the "direct three steps" reduction of the NB molecule is competes a "condensation/reduction" route implying larger molecules.…”

Magnetic metal–organic framework composites: structurally advanced catalytic materials for organic transformations

“…To date, several homogeneous catalytic systems based on transition metal complexes of Rh, Ir, Ru, Au, Ag, Pd, Pt have been reported in literature. [174][175][176] Nevertheless, these expensive catalytic systems are also accompanied with the metal contamination and product purification problems. Therefore, the scientific fraternity has been aiming towards creating heterogeneous catalysts integrated with magnetic characteristics.…”

Coupling of nitrobenzene hydrogenation and 1, 4-butanediol dehydrogenation for the simultaneous synthesis of aniline and γ-butyrolactone over copper-based catalysts

“…The NB to AN conversion rate was as follows: 10CS>10CM>10CA>10CMA. The selectivity of AN was not affected by the support, showing that both the acid and base supports are more favorable for AN formation [3][4][5][6]. The conversion of NB depends on the nature of the support because moderate acid sites are more favorable.…”

“…Aniline (AN) is one of the most versatile chemicals for synthesizing plastics and agricultural products. It is produced mainly from the hydrogenation of nitrobenzene (NB) under noble metal catalysts with high-pressure hydrogen and high temperatures [2,3]. However, the entire process is expensive and not economically feasible.…”