Partial Oxidation of Methane over Functionalised Zeolites and Zeotypes
Doktorsavhandling, 2018

Partial oxidation of methane to methanol is an industrially important process that allows natural gas and biogas to be utilised for methanol-based production of chemicals or converted to liquid methanol fuel, which make transportation more facile. In this thesis, the activity for partial oxidation of methane to methanol over copper functionalised zeolites and silica supported copper is investigated using a three-step quasi-catalytic approach including catalyst activation, methane reaction and methanol extraction by water. Methanol is produced over isolated copper ions but likely not over copper particles. Under methane oxidation conditions, in situ infrared spectroscopy measurements show the formation of methoxy species adsorbed on the Brønsted acid sites, which is concluded to be an important reaction intermediate in the methanol formation.
 
The dynamic interaction between methanol and copper zeolites was experimentally studied by temperature-programmed desorption of methanol using a chemical flow re-actor and in situ infrared spectroscopy and theoretically by first-principles calculations. It is shown that methoxy species binds strongly to the Brønsted acid sites in the zeolites, which explains the need for the extraction step as to obtain methanol from zeolite-based systems. The results indicate that methanol formation and desorption without using water extraction may require a catalyst with lower acidity.
 
The last part of this thesis investigates the possibility of tuning the catalyst acidity by synthesising so-called zeotypes to replace the zeolites. A boron silicate with chabazite structure and lower acidity compared to zeolitic chabazite was synthesised and functionalised with copper. Upon methane exposure to the copper boron silicate, methoxy species forms and retains on the copper sites, which is promising for methanol production. Further, three iron and/or aluminium containing silicates with MFI structure were synthesised. Through infrared spectroscopic surface analysis, it is shown that their acidity is lower than that of the corresponding zeolite structure, and thus these materials may be potential catalyst candidates that deserves further studies.

Cu-ZSM-5

Biogas

Zeolite

FTIR

Cu-SSZ-13

Temperature-programmed desorption

Copper boron silicate

zeotype

Natural gas

Green methanol

In situ infrared spectroscopy

Heterogeneous catalysis

PJ-salen
Opponent: Stian Svelle, Universitet i Oslo

Författare

Xueting Wang

Chalmers, Kemi och kemiteknik, Tillämpad kemi, Per-Anders Carlsson Group

Methane Adsorption and Methanol Desorption for Copper Modified Boron Silicate

RSC Advances,; Vol. 8(2018)p. 36369-36374

Artikel i vetenskaplig tidskrift

Methanol Desorption From Cu-ZSM-5 Studied by In Situ Infrared Spectroscopy and First-Principles Calculations

Journal of Physical Chemistry C,; Vol. 121(2017)p. 27389-27398

Artikel i vetenskaplig tidskrift

X. Wang, N. M. Martin, J. Nilsson, J. Gustafson, S. Carlson, M. Skoglundh and P.-A. Carlsson; Copper Modified Zeolites and Silica for Conversion of Methane to Methanol

X. Wang, A. A. Arvidsson, A. Hellman M. Skoglundh and P.-A. Carlsson; Speciation of Gas Phase Products from zeolites and Cu-zeolites during Temperature Programmed Desorption of Pre-adsorbed Methanol

S. Creci, X. Wang, P.-A. Carlsson and M. Skoglundh; Tuned Acidity for Catalytic Reactions: Synthesis and Characterization of Fe- and Al-MFI Zeotypes

Abundant natural gas, containing mostly methane (CH4), provides a source of energy as well as carbon and hydrogen for chemicals production. A large amount of natural gas, however, is wasted through flaring at oil production sites due to the lack of transportation infrastructure. Converting natural gas to methanol (CH3OH), which is a liquid, would provide a beneficial route towards increased utilisation of natural gas as methanol transportation is rather facile. In fact, methanol is one of the important chemical feedstocks in the chemical industry. In the longer perspective biomethane produced from biomass would realise a green methanol production with low carbon footprint. 
 
This work focuses on catalysts for once-through conversion of methane to methanol at ambient pressure and low temperature. In this, one faces great challenges due to that both methane and oxygen (O2) must be activated while formed methanol should be preserved. Breaking the chemical bonds in methane and oxygen, even when using a catalyst, requires considerable energy input (temperature) that often ruins the production of methanol as it easily decomposes. Inspired by the structure and functionality of natural enzymes that convert methane to methanol under ambient conditions, metal containing zeolites have been considered to be appropriate inorganic catalyst counterparts. One great challenge, however, is methanol desorption from the metal containing zeolites, which is realised through an extraction step.
 
This thesis reports studies on different copper containing zeolites (Cu-zeolites) for partial methane oxidation to methanol. Particular attention is paid to facilitate the liberation of methanol from the Cu-zeolites by desorption experiments. The results suggest that the zeolite acidity plays an important role for desorption of methanol. With this as point of departure, the acidity of zeolites was tuned in an attempt to govern the methanol desorption. Several modified materials were successfully synthesised of which one showed promising results in methane oxidation experiments.

Ämneskategorier

Annan kemiteknik

Annan kemi

ISBN

978-91-7597-817-8

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4498

Utgivare

Chalmers tekniska högskola

PJ-salen

Opponent: Stian Svelle, Universitet i Oslo

Mer information

Senast uppdaterat

2018-11-07