Defective NH2-UiO-66 (Zr) effectively converting CO2 into cyclic carbonate under ambient pressure, solvent-free and co-catalyst-free conditions

Abstract

In this study, a series of metal–organic frameworks (MOFs) NH 2 -UiO-66- x HAc catalysts were synthesized by solvothermal method using acetic acid (HAc) as a modulator, and were applied to the cycloaddition of CO 2 and epichlorohydrin (EPIC) under ambient pressure. Influences of the modulation by HAc on morphologies and structures of the MOFs are demonstrated via PXRD, FESEM, FTIR, N 2 adsorption–desorption, XPS and 1 H NMR characterizations. The results show that the MOFs containing mesoporous pores can be prepared by adjusting the concentration of HAc. By optimizing the amount of HAc added, the specific surface area of NH 2 -UiO-66-8HAc is as high as 879.17 m 2 ·g −1 , which is 28.3% higher than that of the original MOFs. And the evaluation of catalytic performance showed that HAc modulation enhanced the activity of NH 2 -UiO-66- x HAc under mild conditions. The exposure of Lewis acid sites, increased specific surface area and porosity via the modulation of HAc defective ligand can be supposed the key factors to determine the enhanced catalytic activities. In addition, considering the influence of gas concentration on the reaction, the concept of TOP (Turnover of Pressure, defined as the mass of conversions of a unit mass catalyst under unit pressure and unit time) was first proposed in this article.