Sulfation of Metal-Organic Frameworks: opportunities for acid catalysis and proton conductivity

by M.G. Goesten, J. Juan-Alcaniz, E.V. Ramos-Fernandez, K.B. Sai Sankar Gupta, E. Stavitski, H. Van Bekkum, J. Gascon, F. Kapteijn
Year: 2011 ISSN: DOI: 10.1016/j.jcat.2011.04.015

Bibliography

M.G. Goesten, J. Juan-Alcaniz, E.V. Ramos-Fernandez, K.B. Sai Sankar Gupta, E. Stavitski, H. van Bekkum, J. Gascon, F. Kapteijn, Journal of Catalysis 281 (2011) 177-187, Sulfation of Metal-Organic Frameworks: opportunities for acid catalysis and proton conductivity

Abstract

​A new post-functionalization method for metal–organic frameworks (MOFs) has been developed to introduce acidity for catalysis. Upon treatment with a mixture of triflic anhydride and sulfuric acid, chemically stable MOF structures MIL-101(Cr) and MIL-53(Al) can be sulfated, resulting in a Brønsted sulfoxy acid group attached to up to 50% of the aromatic terephthalate linkers of the structure. The sulfated samples have been extensively characterized by solid-state NMR, XANES, and FTIR spectroscopy. The functionalized acidic frameworks show catalytic activity similar to that of acidic polymers like Nafion® display in the esterification of n-butanol with acetic acid (TOF ∼ 1 min−1 @ 343 K). Water adsorbs strongly up to 4 molecules per sulfoxy acid group, and an additional 2 molecules are taken up at lower temperatures in the 1-D pore channels of S-MIL-53(Al). The high water content and Brønsted acidity provide the structure S-MIL-53(Al) a high proton conductivity up to moderate temperatures.

Keywords

Metal–organic frameworks MIL-53 MIL-101 Esterification Proton conductivity Flexibility