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?
Artikel i vetenskaplig tidskrift, 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

Författare

Adam Arvidsson

Chalmers, Fysik, Kemisk fysik

Kompetenscentrum katalys (KCK)

Vladimir Zhdanov

Kompetenscentrum katalys (KCK)

Chalmers, Fysik, Kemisk fysik

Per-Anders Carlsson

Kompetenscentrum katalys (KCK)

Chalmers, Kemi och kemiteknik, Tillämpad kemi, Teknisk ytkemi

Henrik Grönbeck

Chalmers, Fysik, Kemisk fysik

Kompetenscentrum katalys (KCK)

Anders Hellman

Kompetenscentrum katalys (KCK)

Chalmers, Fysik, Kemisk fysik

Catalysis Science and Technology

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

Vol. 7 7 1470-1477

Tidsupplösta in situ metoder för design av katalytiska säten för hållbar kemi

Vetenskapsrådet (VR), 2013-01-01 -- 2016-12-31.

Ämneskategorier

Fysikalisk kemi

Kemiska processer

Atom- och molekylfysik och optik

Annan fysik

DOI

10.1039/c6cy02521h

Mer information

Senast uppdaterat

2018-10-27