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Metal Organic Framework mediated synthesis for novel catalysts in the Fischer Tropsch synthesis.

Periodic Reporting for period 1 - PyroMOF2cat (Metal Organic Framework mediated synthesis for novel catalysts in the Fischer Tropsch synthesis.)

Reporting period: 2016-09-01 to 2018-08-31

The field of heterogeneous catalyst design calls for appropriate preparation concepts leading to highly active, selective and stable catalysts with predictable properties. Gaining control over the size and homogeneity of the active particles and the pore structure of the support are key to develop optimized catalysts.
The practical importance of heterogeneous catalysis is huge in this our civilized life. Not only fuels, fabrics, flavours, fragrances, fertilizers and most pharmaceuticals are generated catalytically but also many of the molecular building blocks for the production of a wide range of the commodities used in everyday life[1]. In this sense, developing catalysts with improved performance in terms of activity, selectivity, stability and tolerance towards different feed supplies is of the utmost importance.
Engineering heterogeneous catalysts with molecular precision is an ongoing challenge that may eventually allow the rational design of materials with predictable properties. In this regard, metal organic frameworks (MOFs) are crystalline compounds consisting of infinite lattices built up of inorganic metal ions or clusters and organic linkers connected by coordination bonds [2]. The high versatility in MOF design provides clear advantages for catalysis, since it should be possible to rationally design both the active site and its environment with very high precision.
Moreover, in recent years, the MOF mediated synthesis (MOFMS) has emerged as a promising technique to obtain improved catalysts. The MOFMS basically consists in heating up the MOF until its framework collapses giving place to different types of materials. Under air, the organic linker is burned away and the metal ions/clusters lead to the corresponding metal oxide. The technique provides control over the shape, composition and the porosity of the resulting oxide. Under inert atmosphere, the organic linker and the metal ions are transformed into the carbon matrix and the metal nanoparticles (NPs), respectively. In this case the MOFMS is able to deliver high metal loading with controlled and homogeneous size of the NPs.
According to these premises, the overall objectives of this project are i) to develop novel catalysts from MOFs and via the MOFMS which are active, selective and stable for different catalytic processes and ii) to understand, control and thus be able to predict the final outcome of the MOFMS using different synthesis conditions.

1. Thomas, J.M. The societal significance of catalysis and the growing practical importance of single-site heterogeneous catalysts. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 2012.
2. Gascon, J., et al., Metal Organic Framework Catalysis: Quo vadis? ACS Catalysis, 2014. 4(2): p. 361-378.
In view of this, the first task of the project consisted in modelling the MOFMS. To do so different conditions (temperature, heating ramp and dwelling time) were applied to different MOFs and the process was modelled by means of solid state conversion models. This allowed to understand the mechanism the MOFMS takes place through and also to predict the final properties of the resulting materials, such as the obtained metallic species and the nanoparticle sizes.
With this knowledge, different novel catalysts were designed next. First, mixed metal oxides from bimetallic MOFs were successfully developed for the CO oxidation reaction. Then, improved Co based catalyst supported on carbon were engineered for the low temperature Fischer-Tropsch Synthesis (LTFTS) using different heating atmospheres. Finally, the CO2 hydrogenation reaction was approached using MOFs with different and new metals to the process. In these three last cases, the working procedure was the same. First, the synthesis of the MOF itself and the conditions of the MOFMS were optimized making use of different basic characterization techniques, such as N2 adsorption-desorption, Powder X-ray diffraction (PXRD), Thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM). After thorough analysis of these results, the catalysts with the most promising properties were tested in the corresponding reaction. Catalytic results were analyzed and the properties of the catalysts before and after reaction were measured using additional characterization techniques such as Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD), Transmission Electron Microscopy (TEM), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS), among others.
The 2 year-project has allowed us to deepen and progress in the recently developed MOF mediated synthesis technique and its application in thermal catalysis. Our work provides new and solid understanding on the pillars of the technique: from its basics, where thermodynamics are able to predict the metallic state of the resulting nanoparticles, through the parametric study which gives the conditions necessary to obtain the desired properties of the obtained materials, such as porosity, particle size and metal loading and up to the catalytic performance of the resulting MOF derived catalysts.
The MOF mediated synthesis and its catalytic applications