Bioinspired solid catalysts for the hydroxylation of methane vorgelegt von M. Ha Vu Le geb. in Quang Ngai, Vietnam von der Fakultät II – Mathematik und Naturwissenschaften der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften Dr. genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof.
Reinhard Schomäcker Gutachter: Prof. Arne Thomas Gutachter: Prof. Christian Limberg Tag der wissenschaftlichen Aussprache: 19. März 2018 Berlin 2018 Acknowledgements I am finally able to submit my own thesis.
Methanol is highly toxic to humans but all I have wished during the PhD time. I had always thought that the direct synthesis of methanol from methane is facile and industrialized already until I became a member in this UniCat project. Production and quantification of methanol with tiny amounts were my obsessions and I often wondered what I should do next and how I could complete my work. That is a difficult but beautiful and memorable period I have spent with my team, with Berlin, and with Deutschland.
First and foremost, I would like to express my gratitude to my main supervisor, Prof. He taught me the way to begin and develop such a changeling study based on previous reports. Working with him, I learned very much from the discussions, questions and comments in our group seminars, and certainly the fast and detailed corrections of my drafts. Actually, his timely encouragements and great passion for chemistry and materials have pushed me up and given me more self-confidence.
Dear Boss, thank you for your guidance and friendliness! I thank Prof. Reinhard Schomäcker not only for agreeing to be my second supervisor but also for the great support during my work. He provided the best conditions for me to conduct and extend the study in different protocols. His wide experience in catalysis and fruitful ideas have helped me resolve many problems and surprisingly improved the experiments.
Our achievements indeed proved that tracking catalysis is possible and we should plan for it step by step, as he has advised me. Especial thanks have to be for Samira Parishan and Maximilian Neumann. I am very lucky to work with them in such a completely new research. These colleagues are so important that I would be impossible to obtain many achievements without their helps.
To Gabrille Vetter, a strict but wonderful technician of AK Schomäcker: Thanks a lot! I would also like to thank Dr. Annette Trunschke, Dr. Hamideh Ahi, Maike Hashagen, and Jutta Kröhnert, who gave me a chance to work at the FHI and then have produced remarkable analytical results. Formal thanks go to Prof.
Christian Limberg, Dr. Fabian Schax, and Marie-Louise Wind for the collaboration on this bioinspired project. Although the materials were not efficient as expected, I believe that we are now on the way to see a miracle. I want to thank Dr.
Jean-Philippe Lonjaret, Nina Hunsicker, Joanna Kakitek, and BIG-NSE students, the 2013 batch in particular, for assisting me to begin the PhD time in Berlin and make it more colorful. looked after us as a second father in the initial period and is always willing to listen to any trouble from these “special children”. To all member of AK Thomas, Amitava Acharjya, Nicholas Chaoui, Christina Eichenauer, Sabrina Fischer, Daniel Hagemeyer, Dr. Mirriam Klapproth, Michaela König, Sophie Küchen, Shuang Li, Meng-Yang Ye, Dr.
Pradip Pachfule, Dr. Jérôme Roeser, Anton Sagaltchik, Sarah Vogl, Dr. Johannes Schmidt, Anne Svilarov, Thomas Langenhahn, Dr. Matthias Trunk, Maria Unterweger, Xiaojia Zhao, Svetlana Barg, Dr.
Daniel Becker, Dr. Hakan Bildirir, Dr. Elham Baktash, Dr. Hefeng Cheng, Dr.
Caren Göbel, Dr. Ali Yassin, Prof. Kamalakannan Kailasam, Dr. Robert Dawson, and Dr.
Robin White: Thank you so much! We are the perfect team I have dreamed of. It is my honor to be a member of the more and more powerful kingdom led by a "Paper Machine" with a "Poster Queen" and a "Photocatalytic King". I like to express especial thanks to our beautiful secretaries, Anne Svilarov and Svetlana Barg, for the great support, to Michaela König for some crazy things we have done together recently, Sophie Küchen for the “so-called German mission”, Amitava Acharjya – my clever “long-term” roommate, and Dr. Robin White for always encouraging me.
I must thank Prof. Nam Phan, Assoc. Nhan Le, Assoc. Quan Pham, and Assoc.
Phong Mai, who did their best to “kick” me to Europe to further learn and improve myself. Dear Ka, I could not go to the present point without you. Thank you for being with me all the times. Certainly, I cannot forget to thank Hoang Phuoc.
He is most like my older brother. To my friends, Hai Yen (Mong Bep!!!), Minh Hieu, Hai Anh, Kim Hoang, Duy Khiet, Cam Loan, Thi Binh, Dr. Phuong Nguyen, Dr. Yen Nguyen, Binh Trong, Dr.
Nga Nguyen, Dr. Nhan Nong, Dr. Thang Pham, Dr. Tien Le, Dr.
Hanh Le, Dr. Anh Phan: thanks to you, my heart has got much warmed up in the “winters” of Germany. Finally, I am grateful to my big family, Dad, Mum, Ti, and my relatives for building my life by the huge love and strong faith in me. I missed being beside them in the worst moments, whose truths are still difficult to be accepted so far.
I expect to see you all soon. Dear grandfather and grandmothers, thank you for being a strong wall to protect me. I am really proud of you. Lúc bắt đầu đi học, đây là giây phút cháu mong chờ nhất, để viết những cảm ơn trong luận văn của mình.
Nhưng cháu không hề nghĩ giây phút này lại buồn đến như vậy. Cảm ơn dì vì đã chăm sóc, yêu thương, luôn tin tưởng và tự hào về cháu. Cháu và mọi người nhớ dì nhiều lắm. “Other things may change us, but we start and end with the family.” (Anthony Brandt) Abbreviations Abbreviations Abbreviation Description BAS Brønsted acid sites bcm Billion cubic meters BET Brauner-Emmett-Teller DFT Density functional theory DME Dimethyl ether DRM Dry reforming of methane EDX Energy dispersive X-ray spectroscopy EPR Electron paramagnetic resonance EXAFS Extended X-ray absorption fine structure FID Flame ionization detector FT-IR Fourier-transform infrared spectroscopy GC Gas chromatography GTL Gas to liquid ICP Inductively coupled plasma MFI Framework type of ZSM-5, silicalite-1 MOR Framework type of mordenite MMO Methane monooxygenase MMT Million metric tons MS Mass spectrometry MTBE Methyl tert-butyl ether MTG Methanol to gasoline MTO Methane to olefins NADH Nicotinamide adenine dinucleotide NLDFT Non-local density functional theory NOCM Non-oxidative coupling of methane OCM Oxidative coupling of methane pMMO Particulate methane monooxygenase i Abbreviations PXRD Powder X-ray diffraction RT Room temperature sMMO Soluble methane monooxygenase TAME tert-Amyl methyl ether TEM Transmission electron microscopy TEOS Tetraethyl orthosilicate TGA Thermogravimetric analysis TON Turnover number TPR Temperature programmed reduction UV-vis Ultraviolet-visible wt.% Weight percent XANES X-ray absorption near edge structure XPS X-ray photoelectron spectroscopy XRD X-Ray diffraction ZSM-5 Zeolite Socony Mobile-5 ii Abstract Abstract Abundant and cheap resources including natural gas, methane hydrates, and biogas, whose major component is methane, have been considered as promising alternatives to decline the dependence of chemical and energy industries on crude oil.
However, there is currently an underutilization of these resources, especially due to the costly transportation and storage, and high chemical inertness of methane. The one-step conversion of methane to more energy-dense liquid derivatives such as methanol is an economically efficient strategy to utilize the great potential of methane. Over the last decades, great interest and numerous efforts have been devoted to direct methane conversion processes with the aim of improving reactivity and selectivity of catalysts toward desired products. Many synthetic catalysts are inspired by the exceptional performance of Fe- and Cu-dependent enzymes (methane monooxygenases) in methanotrophs for the hydroxylation of methane under ambient conditions.
In this contribution, the development and use of bioinspired solid catalysts for the partial oxidation of methane to methanol by either H2O2 or O2 at low temperature are presented. The first part of the thesis focused on the methanol production over Fe-containing zeolites using H2O2 as an oxidant. The catalytic activity of these catalysts was found to be dependent on the protocol used to load Fe species into the zeolite framework. Fe-exchanged ZSM-5 activates H2O2 and methane, respectively, at a previously proposed diiron site, yielding methyl hydroperoxide (MeOOH) as an intermediate.
To obtain high yields of methanol upon decomposition of MeOOH, the formation of highly reactive hydroxyl radicals, which can further oxidize MeOOH into unwanted products, should be controlled by adding Cu species and performing the reaction under mild conditions. On the other hand, extra-framework Fe species in Fe-silicalite-1, proposed to be isolated sites due to the low overall Fe content (0.%), were obtained via hydrothermal synthesis and subsequent thermal treatment. Such isolated Fe sites are capable of converting methane to methanol via facilitating the formation of the hydroxyl radicals like a Fenton system. Zeolites loaded with Cu species are inactive in the above mentioned H2O2-mediated system but known as the most efficient catalysts for the stepwise oxidation of methane to methanol by O2.
In the next chapter, it is described that the Cu-exchange protocol had a considerably influence on the methanol production. Solid-state ion-exchanged Cu/mordenites exhibited a much higher activity than the ones prepared by a conventional liquid-phase procedure. From temperature- programmed reduction by H2 and infrared spectroscopy measurements, it was concluded that the iii Abstract solid-state protocol accelerates the Cu exchange at the small pores of mordenite, where the most active Cu species are preferably located. In situ UV-Vis spectroscopy showed that different active Cu clusters are formed in the catalyst upon the treatment in O2.
After the activation of methane, different intermediates seem to be formed and stabilized at the Cu sites. The main intermediate is a methoxy species, which can be further converted to methanol or dimethyl ether (DME) via the reaction with water or methanol, respectively. Furthermore, within the next chapter it was demonstrated that CuO species supported on SBA-15 are able to react with methane and subsequently produce methanol with a high selectivity (> 84%) via water-assisted extraction. The cluster size of the CuO species can be varied by the Cu- compounds applied for preparing the catalyst, leading to different catalytic performances.
It was proposed that highly dispersed small CuO clusters are responsible for the activity. iv Table of contents Table of Contents Acknowledgements .1 Utilization of methane in chemical industry .2 Commercialized methane conversion processes .2 Synthesis of methyl halides .3 Non-catalytic synthesis of acetylene .4 Synthesis of hydrogen cyanide .3 Promising direct routes of catalytic methane conversion .1 Oxidative coupling of methane .2 Non-oxidative coupling of methane .3 Partial oxidation of methane to C1 oxygenates.2 Bioinspired, low-temperature conversion of methane to methanol.1 Present methanol production .2 Enzymatic production of methanol from methanol .3 Scope of the thesis. Aqueous-Phase Hydroxylation of Methane Catalyzed by Fe- and Cu-Containing Zeolites.2 Synthesis of materials .2 Solid-state ion exchange .4 Results and discussion. 58 v Table of contents Chapter 3.
Improved Cu/Mordenite Catalysts for the Direct Conversion of Methane to Methanol .2 Synthesis of materials .1 Conversion of commercial mordenites to the Na- or NH4-form .2 Solid-state ion exchange .3 Liquid-phase ion exchange .4 Results and discussion. SBA-15-Supported Cu Catalysts for the Methane-to-Methanol Conversion.2 Synthesis of materials .1 Synthesis of SBA-15 .2 Synthesis of CuO/SBA-15 by wet impregnation with common Cu sources .3 Synthesis of Cu siloxide/SBA-15.4 Results and discussion.1 CuO/SBA-15 based on common Cu sources .2 Cu siloxide/SBA-15. Conclusions and Outlook. Characterization of Materials.
a Publications and Presentations. Chapter 1 Introduction 1 Chapter 1.1 Utilization of methane in chemical industry 1.1 Methane potential When the late-18th-century Italian physicist Alessandro Volta first identified methane as an inflammable gas in the bubbles that were released from waterlogged marshes, he could not foresee the great importance of this gas to human society in the following centuries.1 Nowadays, methane is not only an energy source applied in both industrial and domestic scales but also a promising carbon feedstock for chemical manufacture.1 Methane is the major component of natural gas (55–99.