Role of ZnNb2O6 in ZnO-promoted amorphous-Nb2O5 supported Ru catalyst for the partial hydrogenation of benzene

Ruthenium catalysts supported on zinc-promoted amorphous-niobium mixed oxides were prepared, characterized, and studied in the additive-free partial hydrogenation of benzene reaction. The amorphous matrix of Nb2O5 was responsible for a highly active Ru/Nb2O5 catalyst, although less selective than those containing zinc. The ZnO-containing supports were prepared by wet impregnation technique, followed by incipient wetness of ruthenium chloride salt. The catalysts were characterized by textural analysis, X-ray fluorescence, X-ray diffraction, H-2 chemisorption, temperature-programmed reduction (TPR), Scanning electron microscopy, H-2 temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS) of the calcined-reduced samples. Chlorine retention was observed on zinc-containing samples. An unexpected ZnNb2O6 oxide phase, ascribed to a selectivity increase with less activity loss, was obtained for the supports at lower temperatures than those related on the literature. A very complex electronic environment of Ru- and Zn-containing species interactions was observed by TPR. The presence of surface-reduced (Ru-0) and partially reduced (Ru delta+) Ru species observed by XPS justified well, respectively, the activity and selectivity achieved with every catalyst. The addition of water as a solvent resulted in very constant yield to cyclohexene, as expected, despite activity diminution due to low solubility of the reactants. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Ruthenium catalysts supported on zinc-promoted amorphous-niobium mixed oxides were prepared and characterized in this study using various techniques such as X-ray analysis and H-2 chemisorption. It was found that catalysts containing zinc showed higher selectivity, while those without zinc exhibited higher activity.