Effects of Support Types and Their Porosity Characteristics on the Catalytic Performance of Ni-Based Catalysts in Nitrobenzene Hydrogenation to Aniline

Abstract

Ni-based catalysts are increasingly being used in nitrobenzene hydrogenation. How to select suitable catalyst supports is crucial for upgrading the catalytic performance. Herein, three Ni-based catalysts supported on activated carbon fiber (ACF), mesoporous carbon black (CB), and γ-Al2O3 were tested for nitrobenzene hydrogenation. The influence of catalyst supports, their porosity characteristics, and reaction conditions on the catalytic performance was investigated. The results show that 10 wt % Ni/CB catalyst owns an ultrafine active Ni nanoparticles (∼10 nm) with a uniform dispersion and thus exhibits the optimal catalytic activity. The conversion of nitrobenzene and the selectivity to aniline could reach nearly 100% at 120 °C for 1 h. By contrast, it takes 2 h to achieve the same conversion for 10 wt % Ni/ACF at 120 °C, whereas 10 wt % Ni/Al2O3 needs a severe reaction at 150 °C for 2 h. The turnover frequency of 10 wt % Ni/CB approaches 38 h–1, which is higher than those of other catalysts. Nitrobenzene hydrogenation over different catalysts conforms to a first-order reaction, and the apparent activation energy of 10 wt % Ni/CB (42.6 kJ/mol) is significantly lower than that of 10 wt % Ni/Al2O3 (66.0 kJ/mol). Moreover, 10 wt % Ni/CB catalyst exhibits a good recyclability and structural stability owing to the existence of abundant mesopores in CB, in comparison with 10 wt % Ni/ACF and Ni/Al2O3. It is the mesopores rather than the micropores in carbon supports to postpone the deactivation of Ni-based catalysts. This work demonstrates the superiority of porous carbons as catalyst supports over Al2O3 in nitrobenzene hydrogenation.

Adsorption-Dependent H2O Effect for Nitrobenzene Hydrogenation to Aniline over Pt and Ni Catalysts

“…Corma et al have proposed a new deoxygenation path (Scheme S1) on the oxophilic metal Ni catalyst, in which the oxophilic character of Ni strongly facilitates the rupture of the N–O bond, in difference to Pt-based catalysts . To date, heterogeneous catalysts based on supported noble metals like Pt, Pd, or Ru, and non-noble metals like Ni or Co have been identified as effective active centers for nitroarenes reduction, though displaying distinct reaction mechanisms among catalysts. − …”