«Dissertation for the degree of Philosophiae Doctor Marius Westgård Erichsen Department of Chemistry Faculty of Mathematics and Natural Sciences ...»
Mechanistic studies of acid-catalysed
hydrocarbon reactions in zeolitic materials
Dissertation for the degree of
Marius Westgård Erichsen
Department of Chemistry
Faculty of Mathematics and Natural Sciences
UNIVERSITY OF OSLO
© Marius Westgård Erichsen, 2014
Series of dissertations submitted to the
Faculty of Mathematics and Natural Sciences, University of Oslo
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Preface The work presented in this thesis was carried out between August 2010 and June 2014 as part of a four year PhD scholarship financed jointly by the Department of Chemistry, University of Oslo, and the CRI-centre “Innovative Natural Gas Products and Processes” (inGAP). As part of the scholarship, one semester of undergraduate teaching has been performed, and one semester has been spent working for INEOS ChlorVinyls in Porsgrunn. Prof. Unni Olsbye has acted as main supervisor and Prof. Stian Svelle as cosupervisor during the entire project.
I am grateful to Prof. Unni Olsbye for allowing me to perform this work and to both of my supervisors for all their help along the way. Thanks to Terje Fuglerud and the others at INEOS for receiving me and giving me the chance to see how chemistry is used outside academia. Kristof De Wispelaere and others at the Centre for Molecular modelling, Ghent University, are greatly acknowledged for very fruitful discussions and a good collaboration. Thanks to Einar Uggerud and Osamu Sekiguchi at the mass spectrometry laboratory for all their help. I am furthermore grateful that I was allowed to co-supervise Magnus Mortén during an undergraduate project and Christian Ahoba-Sam towards a master’s degree. These experiences as supervisor have been very rewarding for me, and I wish you both the very best for the future.
The entire catalysis group is acknowledged for providing a friendly and stimulating work environment. Special thanks to Bjørn Tore Lønstad Bleken for his willingness to discuss all manner of issues, whether scientific or not, during the years we have shared an office.
Finally, I wish to thank my dear Stine for sticking with me and supporting me despite the long hours I have spent away from home during the last couple of years.
i Abbreviations used in this thesis
HeptaMB+ Heptamethylbenzenium cation HexaMB Hexamethylbenzene HMMC 1,2,3,3,4,5-hexamethyl-6-methylene-1,4-cyclohexadiene HTI Hydrogen transfer index (sum of alkanes / sum of alkenes+alkanes) IZA International Zeolite Association
MeAPO Metal-substituted aluminophosphate MeAPSO Metal-substituted silicoaluminophosphate MeSpaI N(16)-methylsparteinium iodide MeSpaOH N(16)-methylsparteinium hydroxide
iv Table of contents List of publications
The author’s contribution
List of conference contributions
1 Catalysis and zeolitic materials
1.2 Zeolitic materials
1.3 Catalysis by zeolitic materials
1.4 Zeolitic acidity
1.5 Zeolitic structures relevant to this thesis
2 Reactions relevant to this work
2.1 Conversion of methanol to hydrocarbons (MTH)
2.2 De-alkylation of polymethylbenzenes
2.3 Zeolite-catalysed methylation reactions
2.4 Effects of catalyst acid strength
3 Experimental methods
3.1 Synthesis of Zeolitic catalysts
3.2 Synthesis of Hexamethylmethylenecyclohexadiene
3.3 Catalyst characterization
3.4 Catalytic testing
3.5 Mass spectrometry
4 Synopsis of results
4.1 Shape selectivity in the MTH reaction
4.2 Effects of catalyst acid strength
4.3 Polymethylbenzene de-alkylation
4.4 Main conclusions
4.5 Suggestions for further work
Appendix (Papers I-VI)
This thesis is based on the six manuscripts listed and numbered in chronological order below. The full manuscripts are collected in the appendix.
Paper I: H-SAPO-5 as methanol-to-olefins (MTO) model catalyst: Towards elucidating the effects of acid strength.
M. Westgård Erichsen, S. Svelle, U. Olsbye*, Journal of Catalysis, 298 (2013) 94.
Paper II: The influence of catalyst acid strength on the methanol to hydrocarbons (MTH) reaction.
M. Westgård Erichsen, S. Svelle, U. Olsbye*, Catalysis Today, 215 (2013) 216.
Paper III: Shape selectivity in zeolite catalysis. The Methanol to Hydrocarbons (MTH) reaction.
S. Teketel, M. Westgård Erichsen, F. Lønstad Bleken, S. Svelle, K. P. Lillerud, U.
Olsbye*, Catalysis: Volume 26, The Royal Society of Chemistry, 2014, pp. 179.
Paper IV: Syngas to liquids via oxygenates.
M. Westgård Erichsen, J. S. Martinez-Espin, F. Joensen, S. Teketel, P. d. C. Huertas, K. P.
Lillerud, S. Svelle, P. Beato, U. Olsbye*, Submitted as book chapter in “Small-Scale Gas to Liquid Fuel Synthesis”, CRC press Paper V: How zeolitic acid strength and composition alter the reactivity of alkenes and aromatics towards methanol.
M. Westgård Erichsen, K. De Wispelaere, K. Hemelsoet, S. Moors T. Deconinck, M.
Waroquier, S. Svelle, V. Van Speybroeck, U. Olsbye*, Manuscript in preparation.
Paper VI: Reactivity of the heptamethylbenzenium cation – a combined mass spectrometric and catalytic investigation M. Westgård Erichsen*, M. Mortén, O. Sekiguchi, S. Svelle, E. Uggerud, U. Olsbye, Manuscript in preparation.
* corresponding author
Paper I: The author participated in planning the work and performed all the experiments.
The author was strongly involved in data interpretation and preparation of the manuscript.
Paper II: The author performed all experiments and data analysis. The author was also strongly involved in planning the work, interpretation of the results and in preparation of the manuscript.
Paper III: The author performed all new experiments required for preparation of the manuscript (catalytic tests of H-SSZ-24, H-MOR, H-BEA and H-ZSM-22), and was strongly involved in both planning and writing of the manuscript.
Paper IV: The author was strongly involved in the planning and writing of the manuscript.
Paper V: The author planned and performed all catalytic experiments, and was strongly involved in interpretation of the results. The author also prepared the manuscript together with K. De Wispelaere.
Paper VI: The author planned the work, performed all catalytic tests, and prepared the manuscript together with U. Olsbye. Furthermore, the author co-supervised M. Mortén during a Bachelor degree project on synthesis and catalytic testing of HMMC.
viii List of conference contributions Mechanisms of olefin formation in H-SAPO-5 during methanol-to-hydrocarbons (MTH) catalysis.
M. Westgård Erichsen, M. H. Nilsen, K. P. Lillerud, S. Svelle, U. Olsbye Poster presented at the XIIth Netherlands' Catalysis and Chemistry Conference, March 10th-12th, 2011, Noordwijkerhout, The Netherlands Conversion of methanol to hydrocarbons over H-SAPO-5: Towards elucidating the effects of acid strength.
M. Westgård Erichsen, S. Svelle, U. Olsbye Keynote lecture given at SynFuel2012, June 29-30, 2012, Munich, Germany H-SAPO-5 as model catalyst for methanol conversion: Does a lower acid strength shift the alkene formation mechanism?
M. Westgård Erichsen, S. Svelle, U. Olsbye Poster presented for poster symposium at the 15th International Catalysis Conference, July 1-6, 2012 Munich, Germany The influence of catalyst acid strength on reactions relevant to methanol-to- hydrocarbons (MTH) catalysis.
M. Westgård Erichsen, S. Svelle, U. Olsbye Poster presented for poster symposium at Europacat 2013, September 1-6, 2013, Lyon, France The influence of catalyst acid strength on reactions relevant for Methanol To Hydrocarbons (MTH) catalysis.
M. Westgård Erichsen, K. De Wispelaere, J. Van der Mynsbrugge, S. Moors, T.
Deconinck, S. Svelle, K. Hemelsoet, V. Van Speybroeck, U. Olsbye Oral presentation at the 16th Nordic Symposium on Catalysis, June 15-17, 2014, Oslo, Norway
The scope of this PhD project was to study reaction mechanisms and kinetics of acid-catalysed hydrocarbon reactions over zeolitic catalysts, with the effects of catalyst acid strength as the main focus. The first goal was to study in detail the reaction mechanisms of the commercially interesting methanol to hydrocarbons (MTH) reaction over the weakly acidic zeotype H-SAPO-5. Subsequently the structurally identical strongly acidic zeolite H-SSZ-24 should be synthesised, and a detailed comparison of the two catalysts in the MTH reaction performed. The third aim was to study the kinetics of single reactions over these two catalysts.
The large amount of work related to the MTH reaction also led to involvement in studies of other catalysts for the same reaction. For this reason, work and discussions on the MTH reaction constitutes a large portion of this thesis. Two single reaction steps were studied in more detail: methylation and polymethylbenzene de-alkylation. While a full kinetic study of the methylation of benzene and propene over the two catalysts was initiated, it was not completed due to experimental difficulties. Nevertheless, novel results on how acid strength affected methylation of aromatics and alkenes were obtained and are reported here.
The first two chapters of this thesis provide a background for the work performed.
First, general aspects of catalysis and zeolite chemistry are discussed, including a section on acidity. Secondly, an overview of the field of MTH chemistry, de-alkylation and methylation reactions and previous work concerning the effect of catalyst acid strength on reactions is given. Chapter three provides details on experimental methods. Chapter four summarises the work performed during this project. The full details of the work performed can be found in the papers collected in the appendix.
1 Catalysis and zeolitic materials
1.1 Catalysis Catalysis plays an integral part both in most industrial chemical processes and in the chemical reactions of living organisms, and thus impacts strongly on our everyday lives. Stated briefly, a catalyst accelerates a chemical reaction without itself being consumed and without altering the overall thermodynamics of the reaction. This means that catalysis enables reactions to proceed more efficiently and under milder conditions than what would be possible otherwise. An example of how a catalytic reaction differs from a non-catalytic reaction is illustrated by the potential energy diagram in Figure 1.1.
Figure 1.1: Potential energy diagram of a non-catalysed (upper curve) and a catalysed reaction (lower curve).
Figure adapted from .
From Figure 1.1 it is apparent that the catalyst offers an alternative reaction path that is more complex than the non-catalysed path, but contains significantly lower activation barriers. The added complexity is common for catalysed reactions, as some form of bonding between the catalyst and the reactant (substrate) must occur. This inevitably leads to more reaction steps. In order to accelerate the reaction, the catalyst must stabilise the transition state of the reaction more than it stabilises the reactants .
Chapter 1 - Catalysis and zeolitic materials
A second important observation from Figure 1.1 is that the overall energy change from reactants to products is identical in the catalysed and un-catalysed reactions. This means that a catalyst will not in any way affect the position of equilibrium for the reaction.
Catalysis thus falls solely within the field of kinetics.
The word catalysis was first coined by Jöns Jacob Berzelius in 1836 . However, the phenomenon, although not previously defined, had gained practical importance before this. For instance, Humphry Davy had already observed in 1817 that a pre-heated platinum wire would glow white hot in a mixture of air and alcohol or coal gas until all the flammable material was consumed, and Gottlieb Kirchoff had reported the conversion of starch into sugars by dilute acids in 1814 . Even as far back as the 8th century, the writings of the Arabic  (or possibly Persian) alchemist Jabir Ibn Haiyan mention the use of mineral acids for dehydration of alcohol to ether . The first large-scale commercial use of catalysts was made possible by Johan Wolfgang Döbereiner, whose experiments enabled mass production of a lighter based on the incineration of hydrogen over a fine platinum sponge. By 1828, some 20 000 such lighters were in use in England and Germany alone, and it was still in use at the beginning of the First World War [4, 6].
In principle a catalyst can take any form, including atoms, small or large molecules, and solids such as metal or oxide surfaces. It is customary to distinguish between homogeneous catalysis, where the reactants and catalysts are in the same phase, and heterogeneous catalysis, where the catalyst is in a different phase from the reactant. In addition, the field of biocatalysis or enzymatic catalysis is usually treated as a separate discipline. This thesis focuses on heterogeneous catalysis of hydrocarbons in gas phase reacting over solid zeolitic oxide catalysts.
1.2 Zeolitic materials Zeolites are a class of crystalline aluminosilicates with uniform intracrystalline porosity [7, 8]. They are a subclass of the tectosilicates, meaning that they consist of a three-dimensional network of TO4 tetrahedra, where T is either Al or Si. These TO4 units are connected to each other through the oxygen at the vertices, and can assemble into a large variety of microporous (pore dimensions 2 nm ) three-dimensional frameworks.