Metal dimer sites in ZSM-5 zeolite for methane-to-methanol conversion from first-principles kinetic modelling: is the [Cu-O-Cu]2+ motif relevant for Ni, Co, Fe, Ag, and Au?
Journal article, 2017

Direct methane-to-methanol conversion is a desired process whereby natural gas is transformed into an energy-rich liquid. It has been realised at ambient pressure and temperature in metal ion-exchanged zeolites, where especially copper-exchanged ZSM-5 has shown promising results. The nature of the active sites in these systems is, however, still under debate. The activity has been assigned to a [Cu-O-Cu]2+ motif. One remaining question is whether this motif is general and also active in other metal-exchanged zeolites. Herein, we use first-principles microkinetic modelling to analyse the methane-to-methanol reaction on the [Cu-O-Cu]2+ motif, for Cu and other metals. First, we identify the cluster model size needed to accurately describe the dimer motif. Starting from the [Cu-O-Cu]2+ site, the metal ions are then systematically substituted with Ni, Co, Fe, Ag and Au. The results show that activation of Ag and Au dimer sites with oxygen is endothermic and therefore unlikely, whereas for Cu, Ni, Co and Fe, the activation is possible under realistic conditions. According to the kinetic simulations, however, the dimer motif is a plausible candidate for the active site for Cu only. For Ni, Co and Fe, close-to-infinite reaction times or unreasonably high temperatures are required for sufficient methane conversion. As Ni-, Co- and Fe-exchanged ZSM-5 are known to convert methane to methanol, these results indicate that the Cu-based dimer motif is not an appropriate model system for these metals.

Partial Methane Oxidation

Active Site

Cu-ZSM-5

Density Functional Theory

Catalytic Conversion

Zeolite

Microkinetic modelling

Author

Adam Arvidsson

Chalmers, Physics, Chemical Physics

Competence Centre for Catalysis (KCK)

Vladimir Zhdanov

Competence Centre for Catalysis (KCK)

Chalmers, Physics, Chemical Physics

Per-Anders Carlsson

Competence Centre for Catalysis (KCK)

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Applied Surface Chemistry

Henrik Grönbeck

Chalmers, Physics, Chemical Physics

Competence Centre for Catalysis (KCK)

Anders Hellman

Competence Centre for Catalysis (KCK)

Chalmers, Physics, Chemical Physics

Catalysis Science and Technology

2044-4753 (ISSN) 2044-4761 (eISSN)

Vol. 7 7 1470-1477

Time-resolved in situ methods for design of catalytic sites within sustainable chemistry

Swedish Research Council (VR), 2013-01-01 -- 2016-12-31.

Subject Categories

Physical Chemistry

Chemical Process Engineering

Atom and Molecular Physics and Optics

Other Physics Topics

DOI

10.1039/c6cy02521h

More information

Latest update

10/27/2018