In-situ FT-IR Investigation of the Decomposition of Nano Zn4O(C8H4O4)_3 Metal-Organic Framework

摘要

Metal-organic frameworks (MOFs) are a new type of nanoporous materials. MOFs have attracted much attention due to their low-density structures, high surface areas, and tunable frameworks. MOF-5 is a representative Zn-based MOF, in which inorganic [Zn4O]~(6+) clusters combine with organic benzene-1,4-dicarboxylate (BDC) linkers to form a porous Zn4O(BDC)_3 framework with a distance of 12.94 A between the centers of adjacent clusters and an interconnected pore diameter of 8 A. MOF-5 has two typical structures: cubic and tetragonal frameworks. The cubic MOF-5 framework could be synthesized by "diffusion" method. The synthesis approach can generate a high surface area (up to 4000 m~2/g), but takes a long time and consumes a large amount of solvent. In contrast, The "direct mixing" method is a fact and inexpensive approach to synthesize tetragonal nanocrystal MOF-5 framework with a medium BET surface area of 300-1000m~2/g. So far, the nanocrystal MOF-5 synthesized by "direct mixing" method has been widely employed for gas storage, gas separation, heterogeneous catalysis, and other applications. However, the critical issue of MOF-5 as a catalyst is its poor stability, because it can decompose around 400 °C In this work, in-situ FT-IR was employed to reveal the effect of hydrogen on thermal decomposition of MOF-5, which would be important for the application of MOF-5 as hydrogenation catalysts. It was found that the decomposition temperature of MOF-5 is 50°C lower in 3MPa H2 than in vacuum. This happened because the C-H bond formation of MOF-5 in H2 partially destroyed the MOF-5 structures. Furthermore, this was further confirmed by deuterium effect.