Transfer hydrogenation of cinnamaldehyde to cinnamyl alcohol in hydrophobically modified core–shell MOFs nanoreactor: Identification of the formed metal–N as the structure of an active site

Abstract

Zeolitic imidazolate frameworks (ZIFs) were successfully prepared and applied in the environmentally friendly transfer hydrogenation of cinnamaldehyde to cinnamyl alcohol. This was proved to be a homogeneous reaction in heterogeneous system. The experimental results show that ZIFs have better catalytic performance than nitrate. To overcome the recycling of the catalysts, the hydrophobically modified core–shell structure ZIF-67@SiO2-CPTEOS was successfully prepared and hydrogenation took place in this core–shell structure as in a nanoreactor. The reaction rate was enhanced and the active site of the formed metal–N was confined in the core–shell structure nanoreactor. ZIF-67@SiO2-CPTEOS presents better catalytic performance and stability. Furthermore, DFT calculation results show that the activation energy barrier of CoN in ZIF-67 is lower than that of metallic Co dissociated from Co(NO3)2·6H2O, which further confirms that introduction of N and thus the formed CoN bond in ZIF-67 presents higher catalytic activity than that of metal Co. Finally, a possible reaction mechanism is proposed.