Recent experiments show that methane can be oxidized to methanol over zeolites in one step under ambient conditions with a very high selectivity (&gt;90%) [1]. The reaction has been observed to proceed over iron, cobalt and copper exchanged zeolites (Fe-, Co-, and Cu-ZSM-5) [2,3] where the Cu-ZSM-5 system is especially promising as the reaction can take place with molecular oxygen [4]. In this project, we investigate the ZSM-5 zeolite by means of first-principles electronic structure calculations. Together with micro-kinetic modelling, we are able to calculate turn-over-frequencies and thereby, quantitatively, compare different ion-exchanged zeolites and connect to experiments. The electronic structure calculations were made with DFT using an all electron double-numeric basis set with polarized functions (dnp) for all atoms and the gradient corrected exchange correlation functional according to Perdew, Burke and Ernzerhof (PBE). All calculations were done with the DMol3 software [5,6]. Using the same cluster model, exchanging metal ions, we compare activity (turn-over-frequency) between different ion-exchanged zeolites . Results from the DFT calculations and the micro-kinetic modelling clearly show that direct conversion of methane to methanol is possible for this type of active site. Preliminary results for other metal ions indicate that copper has the highest activity. The difference in activity between the different metals follow Sabatier’s principle, where earlier 3d-metals, such as, Ni, Co and Fe are too reactive, and Ag and Au are too noble. [1] A. E. Shilov, A. A. Shteinman, Russ. Chem. Rev. 81 (2012) 291. [2] E. V. Starokon et al., J. Phys. Chem. C 115 (2011) 2155-2161. [3] N. V. Beznis, B. M. Weckhuysen and J. H. Bitter Catal. Lett. 136 (2010) 52-56. [4] J. S. Woertink et al., PNAS 106 (2009) 18908-18913. [5] B. Delley, J. Chem. Phys. 92 (1990) 508-517. [6] B. Delley, J. Chem. Phys. 113 (2000) 7756-7764.

Partial oxidation of methane to methanol over ZSM-5 from first-principles

251st National Meeting (2016)

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