MOF-5 based mixed-linker metal-organic frameworks: Synthesis, thermal stability and catalytic application

Based on the well-known metal-organic framework material MOF-5 we developed a new route for the synthesis of highly porous mixed-linker metal-organic frameworks (MIXMOFs) where 5% and 10% of the benzene-1,4-dicarboxylate linkers have been substituted by a functionalized linker, namely 2-aminobenzene-1,4-dicarboxylate. The thermal stability of the materials decreased with increasing degree of substitution. However, all materials showed thermal stability up to at least 350 °C in oxidizing atmosphere which renders the MIXMOFs promising for catalytic applications. Choosing the optimum ratio of the two linker molecules both the number of active sites and thermal stability of the resulting catalysts could be tuned. The amino group at the functionalized linker proved to be beneficial for the immobilization of Pd species. The Pd loading achieved by equilibrium adsorption could be controlled by the number of NH2 groups in the material. Although the thermal stability of the organic framework was affected to some extent in the presence of Pd, the Pd/MIXMOF materials could successfully be applied as catalysts in the oxidation of CO at elevated temperatures which was chosen as a test reaction.