Partial methane oxidation from electronic structure calculations
Licentiatavhandling, 2017

Investigating catalytic reactions with computational methods is a powerful approach to understand fundamental aspects of catalytic reactions and find ways to guide catalytic design. Partial methane oxidation is one example of a reaction with intriguing challenges, where a detailed atomistic approach may help to unravel the bottlenecks of this, as of yet, inefficient reaction. Although methane only needs one oxygen atom for conversion to methanol, the direct oxidation is difficult; it is in fact so difficult that at many oil extraction sites, the methane that inevitably accompanies the crude oil is flared into carbon dioxide and water as gas-phase methane is too inconvenient to store and transport. The main challenge with partial oxidation of methane is to selectively control the oxidation and steer it towards methanol and prevent over-oxidation to CO2. There exist natural enzymes that can partially oxidize methane to methanol at ambient pressure and temperature, although very slowly. One inorganic analogue to these naturally occurring enzymes are zeolites, a porous material that can readily be synthesized and that have been shown to convert methane to methanol at ambient conditions with a high selectivity (>90 %). This has been realized for zeolites ion-exchanged with different metals, such as iron, cobalt, nickel, and copper. Although there have been many attempts to determine the active site for the reaction, there is still no consensus. One candidate that has been put forth is a [Cu-O-Cu]2+ motif experimentally characterized in the ZSM-5 zeolite. In this thesis, partial oxidation of methane is investigated, focusing on this dimer motif. By combining density functional theory calculations with microkinetic modelling, the catalytic performance of the dimer motif is investigated with a simple reaction mechanism for copper, but also with the copper atoms exchanged with nickel, cobalt, iron, silver, or gold. From these results, it is clear that this particular dimer site is a relevant candidate only for copper, and can be excluded in the continued search for active sites in nickel, cobalt, and iron ion-exchanged ZSM-5. To further understand how methanol is formed and interacts with Cu-ZSM-5, experimental and calculated infrared frequencies are compared for methanol and other adsorbates. The partial oxidation of methane is also studied for other systems with oxidants other than oxygen. In particular, methane oxidation with H2S to CH3SH and H2 is explored on molybdenum sulfide clusters.

ZSM-5 zeolite

density functional theory

microkinetic modelling

Mo6S8 cluster

partial methane oxidation

PJ-salen, Fysikgården 2
Opponent: Prof. Itai Panas, Kemi och Kemiteknik, Oorganisk Miljökemi, Chalmers tekniska högskola

Författare

Adam Arvidsson

Chalmers, Fysik, Kemisk fysik

Xueting Wang, Adam A. Arvidsson, Natalia M. Martin, Johan Nilsson, Stefan Carlson, Johan Gustafson, Magnus Skoglundh, Anders Hellman, Per-Anders Carlsson, Characterization of methanol desorption from Cu-ZSM-5 by in situ infrared spectroscopy and first-principles calculations

William Taifan, Adam A. Arvidsson, Eric Nelson, Anders Hellman, Jonas Baltrusaitis, CH4 and H2S reforming to CH3SH and H2 catalyzed by metal promoted Mo6S8 cluster: a first-principles micro-kinetic study

Ämneskategorier

Oorganisk kemi

Fysikalisk kemi

Fysik

Annan kemiteknik

Teoretisk kemi

Organisk kemi

Drivkrafter

Hållbar utveckling

Styrkeområden

Energi

Materialvetenskap

Fundament

Grundläggande vetenskaper

Utgivare

Chalmers tekniska högskola

PJ-salen, Fysikgården 2

Opponent: Prof. Itai Panas, Kemi och Kemiteknik, Oorganisk Miljökemi, Chalmers tekniska högskola