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Nat Chem. 2019 Feb;11(2):170-176. doi: 10.1038/s41557-018-0171-z. Epub 2018 Nov 19.

Identification of the strong Brønsted acid site in a metal-organic framework solid acid catalyst.

Author information

1
Department of Chemistry, Kavli Energy NanoSciences Institute at Berkeley, and Berkeley Global Science Institute, University of California-Berkeley, Berkeley, California, USA.
2
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
3
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California, USA.
4
Department of Chemistry, Stanford University, Stanford, CA, USA.
5
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
6
Department of Chemistry, Kavli Energy NanoSciences Institute at Berkeley, and Berkeley Global Science Institute, University of California-Berkeley, Berkeley, California, USA. yaghi@berkeley.edu.
7
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. yaghi@berkeley.edu.

Abstract

It remains difficult to understand the surface of solid acid catalysts at the molecular level, despite their importance for industrial catalytic applications. A sulfated zirconium-based metal-organic framework, MOF-808-SO4, was previously shown to be a strong solid Brønsted acid material. In this report, we probe the origin of its acidity through an array of spectroscopic, crystallographic and computational characterization techniques. The strongest Brønsted acid site is shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters. When a water molecule adsorbs to one zirconium atom, it participates in a hydrogen bond with a sulfate moiety that is chelated to a neighbouring zirconium atom; this motif, in turn, results in the presence of a strongly acidic proton. On dehydration, the material loses its acidity. The hydrated sulfated MOF exhibits a good catalytic performance for the dimerization of isobutene (2-methyl-1-propene), and achieves a 100% selectivity for C8 products with a good conversion efficiency.

PMID:
30455431
DOI:
10.1038/s41557-018-0171-z
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