A novel Ru–B/SiO2 amorphous catalyst used in benzene-selective hydrogenation
Introduction
Benzene-selective hydrogenation to cyclohexene caused much attention because the product is an important resource in the polymer industry [1]. However, such a selective hydrogenation seems very difficult because cyclohexene is chemically active owing to its double bond, on which the further hydrogenation to cyclohexane can occur easily. Therefore, the cyclohexane is the main product and the selectivity to cyclohexene is very low during most of the benzene hydrogenation. Since the first benzene-selective hydrogenation on a Ni film was reported in 1957 [2], various catalysts have been designed to improve the hydrogenation selectivity 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. Among them, the Ru-based catalysts, such as Ru powder, Ru black, and Ru powder deposited on a support, have been studied thoroughly. However, most of those catalysts reported so far are not satisfactory, due to their low selectivity in such hydrogenations. Since the 1980s, the amorphous alloy catalysts have become more and more attractive owing to their superior catalytic activity and selectivity [13]. Many Ni-based amorphous alloy catalysts have been prepared by both rapid quenching techniques and chemical reduction 14, 15, 16, 17, 18, 19, 20. However, no report on the Ru-based amorphous alloy catalyst was found in the literature. In this paper, a new supported Ru-based catalyst (Ru–B/SiO2) was prepared by impregnation and chemical reduction with KBH4. The as-prepared catalyst was determined to be in an amorphous state by XRD. In comparison with the corresponding Ru/SiO2 catalyst obtained by H2 reduction, the new catalyst exhibited superior selectivity toward cyclohexene during benzene partial hydrogenation in liquid phase.
Section snippets
Catalyst preparation
The Ru–B/SiO2 sample was prepared in the following procedures. Pre-dried silica (60–80 meshes, 185.0 m2 g−1) was impregnated with a desired amount of RuCl3 solution (0.10 M) to reach a “caking point”. After being dried at 383 K overnight, the above precursor was reduced by adding dropwise 0.20 M KBH4 solution containing 0.020 M NaOH. The molar ratio of B/Ru was 4/1 to ensure that all the Ru3+ ions on the support were completely reduced. During the reaction, the temperature was kept at 273 K in an
Results and discussion
The chemical composition, the Ru loading on the support, the total surface area, and the active surface area of the as-prepared Ru–B/SiO2 and the corresponding Ru/SiO2 catalyst are listed in Table 1. With the same Ru loading, the fact that the surface area of the as-prepared Ru–B/SiO2 catalyst was larger than the area of the corresponding Ru/SiO2 catalyst indicated a higher dispersion of active Ru sites on the surface of the Ru–B/SiO2 catalyst.
According to the XRD pattern of the as-prepared
Conclusions
A new Ru-based catalyst, the Ru–B/SiO2 amorphous catalyst, was prepared by the impregnation and chemical reduction with KBH4. Its amorphous character was determined by XRD and DSC. During the partial hydrogenation of benzene, the as-prepared catalyst exhibited better selectivity toward cyclohexene than the corresponding Ru/SiO2 catalyst reduced by hydrogen. The results could be explained based on the promoting effect of water on the hydrogenation selectivity. The existence of oxidized boron on
Acknowledgements
This work was supported by the National Natural Science Foundation of China. We are also grateful to the SINOPEC for providing financial support for this research.
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