Thermochimica Acta 499 (2010) 71–78 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca MOF-5 based mixed-linker metal–organic frameworks: Synthesis, thermal stability and catalytic application Wolfgang Kleist, Marek Maciejewski, Alfons Baiker ∗ Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, ETH Zurich, Hönggerberg HCI, CH-8093 Zurich, Switzerland article info Article history: Received 6 August 2009 Received in revised form 3 November 2009 Accepted 8 November 2009 Available online 14 November 2009 Keywords: CO oxidation Coordination polymer Metal–organic framework Pd catalyst PulseTA technique TA–MS abstract 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 atmo- sphere 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 immobiliza- tion of Pd species. The Pd loading achieved by equilibrium adsorption could be controlled by the number of NH 2 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. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Since the first reports on porous metal–organic frameworks (MOFs, also known as porous coordination polymers) were pub- lished [1–5], this new material class has attracted enormous interest in the field of material chemistry. A large variety of bi- or multi-functional organic linkers and transition metal units have been applied as building blocks in the last years leading to numer- ous 2D and 3D structures [6–9]. Especially the development of high-throughput assisted preparation techniques represented an important improvement [10,11]. MOF-5, which forms a cubic network from benzene-1,4- dicarboxylate (BDC) and tetrahedral ZnO 4 units, is one of the most famous and best investigated examples for porous 3D-MOFs [12,13]. Yaghi and coworkers demonstrated successfully the syn- thesis of so-called “isoreticular” (=forming the same network) metal–organic frameworks (IRMOFs) by using dicarboxylates with larger organic spacers (e.g. 4,4 ′ -biphenyl-1,1 ′ -dicarboyxlate BPDC = IRMOF-10) or additional functional groups (like 2-amino- benzene-1,4-dicarboxylate ABDC = IRMOF-3) instead of BDC linkers [14]. Using this approach, the synthesis of materials with designed pore diameters and organic linkers bearing additional functional side-groups became feasible. ∗ Corresponding author. Fax: +41 44 63 21163. E-mail address: baiker@chem.ethz.ch (A. Baiker). In general, these metal–organic frameworks feature micro- porous structures exhibiting huge specific surface areas and pore volumes, which renders them, like zeolites, interesting for various applications [15,16]. In the beginning, MOFs have been used mainly for storage of hydrogen or hydrocarbons [14,17–19], but the field of possible applications was soon extended to other important fields such as gas purification [20,21] and separation [15] or sensor tech- niques [22,23]. Implementation of MOFs in catalytic applications is another promising field which has recently attracted the interest of many groups (vide infra). However, for this purpose some important requirements imposed to the framework material have to be taken into account. Most of the MOF structures that have been published in the last years suffer from undesired chemical and/or physical properties which prevent their usage under real reaction conditions. The most important among them are the insufficient thermal stability in air and the lack of tolerance towards moisture and many organic sol- vents. As a consequence, the stability of such framework materials under real reaction conditions has to be considered before they can be applied. Another important aspect concerns the introduction of cataly- tically active sites (acid/basic groups and/or transition metals) into the framework which may also influence the thermal stability of the resulting catalyst. In principle, three different strategies have been reported in the literature up to now (see Fig. 1): in the first approach, the transition metal ions that are part of the framework structure should act as the catalytically active sites (Fig. 1A) [24–26]. The most important prerequisite here is the presence of metal centers 0040-6031/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2009.11.004