Dmitrii Osadchii

dmitri

Van der Maasweg 9, 2629 HZ Delft 
Room E2.140

Tel: *31 (0)15 2786976

D.Osadchii@tudelft.nl




Towards Mild Methane Oxidation

Large natural supplies of methane (as a main component of natural gas) have stimulated the development of technologies to process it into convenient fuels and valuable chemical products for already more than 150 years. However, high flammability added to the remote location of the main natural stocks of methane limits its use, leading to complicated and expensive process of transportation. An alternative can be the oxidative conversion of methane into liquid products of relatively easier and more economical transportation. One of the most desired methane derivatives is methanol, which finds numerous applications in chemical synthesis and is preferred over the deeper methane oxidation products [1, 2]. 

Methane is characterized by the strongest C‒H bond compared to other hydrocarbons, and the products of its partial oxidation are significantly less thermodynamically stable. Thus, achieving high methane conversion and selectivity towards methanol becomes challenging because of overoxidation products are typically more reactive than methane. Nowadays, the industrial production of methanol is achieved via manufacturing of synthesis gas and represents a multi-step, high energy- and resource-consuming process (>800 °C, >50 bar at different stages). Therefore, partial oxidation of methane to methanol is an area of great scientific and economical interest. 

It was shown that at high temperatures (500‒800 °C) methane oxidation predominantly occurs via homolytic C‒H bond cleavage. Hence, high-temperature methane oxidation routes  not only energy costly, but also meet crucial problems of product selectivity [1, 3]. These reasons have stimulated the intense investigation for low-temperature methane oxidation routes (0‒200°C) . Highly-active and selective low-temperature catalytic systems have already been reported [4]. However, these catalysts are still far from industrial application because of various limitations, i.e. the homogeneous nature of some of these catalysts, multi-step synthesis procedures, utilization of noble metal complexes as catalysts, harsh and environmentally unfriendly conditions such as highly acidic solvents and strong oxidants [1], among others. To overcome these limitations, the biomimetic approach is often proposed because of the ability of natural enzymes (methane monooxygenase, MMO) to directly oxidize the methane C‒H bond and other alkanes under mild aqueous conditions. Implementation of the active site, similar to those of MMO, in an appropriate catalyst microstructure to facilitate the desired reaction pathway, is our strategy. One of the most attractive ways is the application of various organic and coordination frameworks as hosts, which structure could be fine-tuned relatively easily [5, 6]. From both an ecological and an economical point of view the ultimate oxidant is dioxygen, representing an additional challenge at low temperature. Current active systems in partial methane oxidation utilize hydrogen peroxide, another “green” oxidant [7]. However, the commercial use of hydrogen peroxide in a large-scale process is not economically viable. Thus, direct synthesis of hydrogen peroxide from H2 and O2 in the reaction mixture would then offer a solution, applicable for operating together with the methane oxidation catalyst. 

The aim of this project is the development of a highly active and selective catalyst for methane to methanol partial oxidation. The main objectives are the synthesis of MOF- or COF-based methane oxidation catalysts, their characterisation and determination of their catalytic properties, utilizing H2O2 as oxidant as a first stage. Furthermore, the development of catalyst for synthesis of H2O2 from H2 and O2, compatible with the methane oxidation catalyst to produce a joint catalytic system, represents the consecutive challenge.


Acknowledgements

This research receives funding from the Dutch National Science Foundation (NWO-CW) / VIDI Grant Agreement n. 723.012.107, MetMOFCat

References

  1. Hammond, C., Conrad, S., Hermans, I. (2012). Oxidative Methane Upgrading. Chem. Sus. Chem., 5(9), 1668–1686.
  2. Olah, G. A. (2005). Beyond Oil and Gas: The Methanol Economy. Angew. Chem. Int. Ed., 44 (18), 2636–2639.
  3. Otsuka, K., Wang, Y. (2001). Direct conversion of methane into oxygenates. App. Cat. A: General, 222, 145–161.
  4. Periana, R. A., Bhalla, G., Tenn, W. J., et al. (2004). Perspectives on some challenges and approaches for developing the next generation of selective, low temperature, oxidation catalysts for alkane hydroxylation based on the CH activation reaction. J. Mol. Cat. A - Chemical, 220(1), 7–25.
  5. Kuhn, P., Antonietti, M., Thomas, A. (2008). Porous, Covalent Triazine-Based Frameworks Prepared by Ionothermal Synthesis. Angew. Chem. Int. Ed., 47, 3450 –3453.
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  7. Hammond, C., Jenkins, R. L., Dimitratos, N. et al. (2012) Catalytic and Mechanistic Insights of the Low-Temperature Selective Oxidation of Methane over Cu-Promoted Fe-ZSM-5. Chem. Eur. J., 18, 15735 – 15745