Synthesis and alcohol catalytic properties of TEMPO functionalized Zr-based MOFs

Abstract

A strategy based on grafting organocatalytic units as side-chain on the organic linkers, a TEMPO radical decorated terphenyl-dicarboxylic acid linker was synthesized. By employing acetic acid as modulator, TEMPO radical decorated UiO-68-TEMPO nanocrystals were synthesized by using H2tpdc-TEMPO as organic linker and ZrOCl2 as metal source under solvothermal conditions. UiO-68-TEMPO are monodispersed nanocrystals with side in the range of 800-1200 nm, with high BET areas (up to 1320 m2/g), and contain a large number of TEMPO radicals as evidenced by solid-state EPR spectrum. UiO-68-TEMPO nanocrystals enable selective oxidation of a broad range of alcohols, including primary aromatic alcohols, secondary aromatic alcohols, and heterogeneous atomic alcohols, with high efficiency and selectivity. The catalytic activity of UiO-68-TEMPO nanocrystals remains 75% after catalysis for four cycles. Finally, a plausible catalytic mechanism for the oxidation of benzyl alcohol by UiO-68-TEMPO was proposed, that is the TBN co-catalyst produces NO2/NO redox mediator, which enables the oxidation of TEMPO radicals to oxoammonium cations by O2, and finally oxidize benzyl alcohol to benzaldehyde.

Keywords

• porous material
• zr-based metal-organic framework
• organocatalyst
• radical
• alcohol oxida-tion