Novel Hierarchical Copper-Based Metal-Organic Frameworks for Improved Catalytic Performance
2019
Introducing
additional meso- or macroporosity into traditionally microporous metal-organic
frameworks (MOFs) is a very promising way to improve the catalytic performance
of these materials, mostly due to the resultant reductions of diffusional
barriers during liquid-phase or gas-phase reactions. Here we show that HKUST-1
can be successfully synthesised either via post-synthetic treatment (etching
prepared HKUST-1 samples in phosphoric acid, here called HKUST AE) or via in situ crystallisation (exposing the MOF
precursor solution to supercritical CO2, here called HKUST CO2)
to produce hierarchically porous structures that are highly beneficial for
catalysis. These hierarchical MOFs were characterised by powder X-ray
diffraction (PXRD), scanning electron microscopy (SEM) and gas sorption to
confirm the preservation of the microscopic structure and the appearance of
macropores in the crystallites. More importantly, the benefits of introducing these
hierarchical porous structures into this MOF for improving the diffusion
accessibility of reagents to the sample in catalysed liquid- and gas-phase
reactions were quantified for the first time. It was found that the
hierarchical pore structure helped to increase the reaction conversion of
styrene oxide methanolysis (by ~65 % using either HKUST AE and HKUST CO2,
at 40 oC in 25 min) and CO oxidation (by 55 % using HKUST CO2
at 260 oC). These findings demonstrate the advantage of using
hierarchical porous MOFs in catalysis.
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