(606g) Zr Metal–Organic Framework As a Catalyst Support for Solid Acid Catalyzed C-C Bond Isomerization and Disporportionation

Acid-catalyzed skeletal isomerizations are important reactions for the petrochemical industries. Hydrocarbons such as hexane and xylene are crucial reactants in the production of basic petrochemicals and fuels, and reactions of these molecules have been model reactions which provide structural information on solid acid catalysts. Among those, o-xylene isomerization/disproportionation is a probe reaction for strong Brønsted acid catalysis, and it is known to be sensitive to the local acid site density and pore structure.

We report on the use of Keggin polyoxometalate (POM) encapsulated within a stable Zr-based metal–organic framework (MOF), NU-1000, as a catalyst for o-xylene isomerization and disproportionation. Extended X-ray absorption fine structure (EXAFS), ³¹P NMR, N₂ physisorption, and XRD show that the catalyst is stable under the reaction condition. Initial rates over the MOF-supported catalyst were comparable to a control WO_x-ZrO₂, however the NU-1000 supported catalyst was unusually active toward the transmethylation pathway that requires two adjacent active sites within a pore, as created when POM is confined in the support. This work shows the promise of metal–organic framework topologies in giving access to unique activity and selectivity, even for aggressive reactions such as hydrocarbon skeletal isomerization.