Highly Efficient Hydrogenation of Nitrobenzene to Aniline over Pt/CeO2 Catalysts: the Shape Effect of the Support and Key Role of Additional Ce3+ Sites

Pt/CeO2 catalysts with different support shapes and prereduction temperatures were prepared and tested in the liquid-phase hydrogenation of nitrobenzene. Detailed characterizations reveal that the support shape effect of Pt/CeO2 catalysts on nitrobenzene hydrogenation originates from the exposed crystal planes on CeO2 with different reducibilities. A high-energy surface is readily reduced to generate more Ce3+ surface sites and oxygen vacancies, not only favoring the dispersion and stabilization of Pt species due to stronger metal-support interaction but also providing more adsorption sites for reactants and intermediates. Reduction treatment at high temperatures has been proved to be an effective way to improve the performance of Pt/CeO2 catalysts by providing additional Ce3+ surface sites and high H-spillover capability. The additional Ce3+ far away from Pt, derived from a high-temperature reduction, can adsorb the N-phenylhydroxylamine intermediate more effectively due to its stronger electron-donating ability and in turn promote aniline formation. It is also found that Na ions with suitable content facilitate the generation and stabilization of surface Ce3+ by charge transfer and help Pt particles to maintain a smaller size. Consequently, a 0.25 wt % Pt catalyst, supported on Na-containing CeO2 nanorods and reduced at 600 degrees C, displays a high level of aniline productivity of 40.8 molAN/gPt/h and excellent stability in nitrobenzene hydrogenation at room temperature. A pathway of nitrobenzene hydrogenation catalyzed by Pt/CeO2 is also proposed.