Metal-organic frameworks (MOFs) with nanopores have been attracted much attention as a platform for absorbing guest molecules and the absorbed molecules in MOFs exhibit the unique physicochemical properties different from those of free gaseous molecules.¹ However, there is poor understanding of how the confined guest molecules affect chemical reactions. To uncover the insight, we designed a hybrid material based on MOFs and metal nanoparticles (NPs), where MOFs provide absorbed molecule as a reactant and metal NPs work as a catalyst.

At first, we prepared 9 nm Pt NPs using a liquid phase reduction method.² Then, the obtained Pt NPs were coated with a thermally stable Zr-based MOF (UiO-66)³ by a solvothermal method in the presence of ZrCl₄ and terephthalic acid. Transmission electron microscopy (TEM) image revealed that the UiO-66 completely covers the Pt surface (Pt@UiO-66). For comparison, we also prepared Pt on UiO-66, where Pt NPs are located on the surface of UiO-66, by mixing Pt NPs and pristine UiO-66 in DMF and centrifuging them. We investigated water-gas shift reaction⁴ activity of Pt@UiO-66 and Pt on UiO-66 by using a fixed bed flow reactor. Both Pt@UiO-66 and Pt on UiO-66 exhibited higher CO conversion than Pt on ZrO₂, demonstrating that the presence of the UiO-66 hybridizing causes an enhancement in the catalytic activity. Interestingly, the activity of Pt@UiO-66 was much higher than that of Pt on UiO-66, demonstrating that the UiO-66 coating enhanced the activity. The detail mechanism on the enhanced activity is also discussed.

References

1. X. Kong, J. R. Long, J. A. Reimer et al., J. Am. Chem. Soc., 2012, 134, 14341.
2. C. Tsung, G. A. Somorjai, P. Yang et al., J. Am. Chem. Soc., 2009, 131, 5816.
3. L. H. Cavka, K. P. Lillerud et al., J. Am. Chem. Soc., 2008, 130, 13850.
4. H₂O + CO → H₂ + CO₂