Ruthenium nanoparticles loaded on multiwalled carbon nanotubes for liquid-phase hydrogenation of fine chemicals: An exploration of confinement effect

• Ru NPs were successfully loaded on the inner or the outer surface of CNTs.
• A confinement effect derived from electronic effect was validated.
• The confinement effect can be enhanced by removing oxygenated surface groups.
• The nature of unsaturated group can change the response to the confinement effect.

For the purpose as stated in title, three Ru catalysts were prepared with the same treated carbon nanotubes. One has most of Ru nanoparticles confined inside the channels, and the other two have most of Ru nanoparticles outside through different preparation methods. Heat treating was performed to obtain another three catalysts. Characterization by X-ray photoelectron spectroscopy indicated that heat treating made Ru nanoparticles electron rich. Hydrogenation of benzene, p-chloronitrobenzene, and cinnamaldehyde was chosen as model reactions to evaluate all these catalysts. Electronic effect plays an important role in catalytic performance. The electron-rich Ru would be favorable for p-chloronitrobenzene hydrogenation, but unfavorable for benzene hydrogenation. For cinnamaldehyde hydrogenation, the electron-rich Ru would be favorable for adsorption of CO bond rather than CC bond and thus promoted the selectivity to cinnamyl alcohol. A confinement effect induced by the electronic effect has different influences on these substrates, and it can be enhanced by heat treating for all the reactions. Finally, we drew a correlation of electronic structures between catalysts and substrates accounting for these phenomena.

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