Synthesis, stability and activity of palladium supported over various inorganic matrices in the selective hydrogenation of nitroaniline

Abstract

This work aimed to study the influence of catalyst supports on their catalytic activity and physico-chemical properties of resulting material. Such supports as SiO2, γ-Al2O3 and carbon containing 3, 4 or 5% palladium are used for the experiments. The hydrogenation of p-nitroaniline is chosen as a model reaction for testing the synthesized catalysts. Catalysts were studied by different physico-chemical methods in order to reveal the structure and its changes in reaction. XPS data shows the catalyst surface changed its chemical structure. The palladium oxidation state strongly depends on the nature of the matrix. For γ-Al2O3- and SiO2-supported catalysts, the formation of palladium(II) oxide was found to take place, at the same time, the carbon support is characterized by the presence of both palladium(II) oxide and palladium(IV) oxide. Such a difference shows that the nature of the support influences the oxidation state of active metal. The application of carbon matrix provides a lower oxidation state of the active metal due to electron density shift to the support. Temperature programmed desorption of NH3 demonstrates γ-Al2O3 to contain weak, medium and strong acid sites, while activated carbon has only medium and weak ones. Silica has only weak acid sites. A correlation between catalyst activity and acid–base properties was shown.