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Insights Into the Acid-Base Properties of Functionalized Multiwall Carbon Nanotubes Klaus Dieter Friedel Ortega

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Insights Into the Acid-Base Properties of Functionalized Multiwall Carbon Nanotubes Klaus Dieter Friedel Ortega Insights into the Acid-Base Properties of Functionalized Multiwall Carbon Nanotubes Klaus Dieter Friedel Ortega Berlin 2014 Insights into the Acid-Base Properties of Functionalized Multiwall Carbon Nanotubes vorgelegt von Diplom-Ingenieur Klaus Dieter Friedel Ortega aus Caracas, Venezuela Von der Fakultät II - Mathematik und Naturwissenschaften der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Ingenieurwissenschaften - Dr.-Ing. - genehmigte Dissertation Promotionsauschuss: Vorsitzender: Prof. Dr. Martin Lerch Berichter/Gutachter: Prof. Dr. Robert Schlögl Berichter/Gutachter: Prof. Dr. Peter Strasser Berichter/Gutachter: Prof. Dr. Jaeyoung Lee Tag der wissenschaftlichen Aussprache: 1. Juli 2014 Berlin 2014 D 83 La filosofía no puede sino beneficiarse de nuestras disputas, porque si nuestras concepciones se prueban verdaderas, se llegará a nuevos logros; y si se prueban falsas, su refutación confirmará aún más las doctrinas originales. Philosophy itself cannot but benefit from our disputes because if our thoughts are true then we will make new gains, and if they are false then their refutation will confirm further the earlier doctrines. Galileo Galilei Acknowledgement Once Sir William Lawrence Bragg stated: “The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them”. Rational, practical, and theoretical knowledge combined with a substantial amount of creativity form altogether the fundamental basis necessary for gaining new perspectives about the macro- and microscopic world we intend to understand. This, in fact, is one the most important lessons I learned during my PhD thesis. However, reaching this status quo would have never been possible without the constant help and support of a long list of colleagues and advisors that accompanied me in the past years, who day by day taught me that cooperative and harmonic work is the only true key leading to success. First and foremost, I would like to express my sincere gratitude to my advisor Prof. Dr. Robert Schlögl, Director of the Department of Inorganic Chemistry at the Fritz Haber Institute of Max Planck Society, for the faith he placed in me from the beginning until the end of my research stay, and for his unconditional support. Thanks to his patience, understanding, guidance, encouragement, and great knowledge I was able to accomplish my PhD project. I would like to particularly acknowledge the members of the doctoral board, Prof. Dr. Peter Strasser and Prof. Dr. Jaeyoung Lee, who gladly accepted to invest their valuable time in reviewing this work. Additional gratitude goes to Prof. Dr. Martin Lerch for taking the chair of the examination board. My special thanks and appreciation goes to my supervisor Dr. Annette Trunschke, leader of the Reactivity group, who warmly welcomed me from the very first day. Her recommendations and regular discussions helped me to develop a critical eye about my own work. Furthermore, I am truly grateful for the time invested in reviewing the extensive paper drafts, and for the resulting feedback. At this point I would like to express my gratitude to all the members of the Reactivity group, not only for the daily support in my research work, but also for the great moments we spent in conferences, after PhD days, during department trips, and in Christmas parties. I am highly grateful and indebted to Dr. Benjamin Frank for providing me not only a comprehensive overview of the research topic, but also for introducing me into the utilization of the home-built TPD setup known as Reverend T. His continuous technical assistance and ideas in general were invaluable in the past years. In a similar manner, I thank my former colleague Pierre Kube for all the knowledge transfer in the field of gas chromatography and for his willingness to help with any kind of technical issue at any time. Further acknowledgment goes to Dr. Benjamin Johnson for the XPS measurements performed over the NCNT samples. With this respect, I am truly grateful to the support offered by Dr. Rosa Arrigo in the time-consuming evaluation of the various XP spectra. Similarly, I would like to express my gratitude to Dr. Sabine Wrabetz for all the efforts made in performing microcalorimetric measurements on various samples that helped me to gain a better understanding of their surface acid-base properties. Herewith I would like to thank Dr. Olaf Timpe and Dr. Gregor Wowsnick for discussing my ideas related with the chemical modification strategies planned and applied to the CNT material. On top of that, I do not know how to express my gratitude for the outstanding and motivating office atmosphere. In a similar way, I would like to thank all my labmates, colleagues, and project partners for every piece of contribution that lead to the success of this work: Prof. Dr. Jean-Phillipe Tessonnier, Dr. Ali Rinaldi, Dr. Sylvia Reiche, Youngmi Yi, Dr. Stefanie Kühl, Mateusz Jastak, Pia Kjær Nielsen, Christian Heine, Dr. Johannes Noack, Pierre Schwach, Dr. Raoul Naumann d’Alnoncourt (Furnace), Dr. Zailai Xie (CarboKat), Jutta Kröhnert (ATR-FTIR), Elif Ider, Dr. Andrey Tarasov (TG-MS), Jasmin Allan (TG-MS), Dr. Marc Willinger, Dr. Thomas Lunkenbein, Dr. Ramzi Farra, Dr. Manfred Schuster (TEM), Norbert Pfänder (TEM), Wiebke Frandsen (SEM/EDX), Dr. Thomas Cotter, Dr. Neil Hamilton, Dr. Stefan Zander, Dr. Timur Kandemir, Maike Hashagen (BET), Dr. Raoul Blume (XPS/BESSY), Dr. Heiner Schwarz, Dr. Juan Velasco Vélez, Prof. Dr. Martin Muhler (CarboKat/Bochum), Dr. Wei Xia (CarboKat/Bochum), Jason Anderson. Last but certainly not least important, I would like to thank my family who has supported me ever since I came to Germany for my university studies in 2005. Although the distance has not allowed us to share important moments, I know they have been there for me whenever I needed them. At this point, however, I would like to express my special love and gratitude to my mother by dedicating some words in my native language to her: “Gracias mamá por todo tu esfuerzo y dedicación. Este es el punto final de un largo viaje y el comienzo de una nueva etapa. Te estaré infinitamente agradecido por haber hecho de mi la persona que soy. Siempre te llevo en mi corazón”. Finally, I would like to deeply thank my girlfriend, Maria Natália Gabriele Moura, an outstanding lovely woman who has supported me every since I met her - muito orbrigado pelo seu suporte incondicional. Kurzfassung Kohlenstoffnanoröhren (CNTs) werden aufgrund ihrer hohen spezifischen Oberfläche, ihrer einzigartigen geometrischen und elektronischen Struktur und der hohen chemischen Sta- bilität als vielversprechende Materialien zur Anwendung in der heterogenen Katalyse diskutiert. Struktur und intrinsische Eigenschaften ihrer Oberfläche können zudem durch Einbau von Defekten, insbesondere durch Funktionalisierung mit Heteroatomen, gesteuert werden. Durch verschiedenartige Funktionalisierungen lassen sich saure oder basische Zen- tren auf der Oberfläche generieren, wodurch CNTs als heterogene Säure-Base-Katalysatoren eingesetzt werden können, aber auch als Trägermaterial z.B. für katalytisch aktive Metalle, da durch gezielte Modifizierung der CNT-Oberfläche Metall-Träger-Wechselwirkungen bee- influsst werden können und damit veränderte katalytische Eigenschaften zu erwarten sind. Um Struktur-Aktivitäts-Korrelationen aufstellen zu können, bedarf es sowohl geeigneter Präparationen zum Erhalt möglichst homogen funktionalisierter Oberflächen als auch belastbarer Methoden zu deren Strukturaufklärung. Die komplexe, stark von den Syn- theseparametern abhängige Oberflächenchemie der CNTs, erfordert dazu die gleichzeitige Anwendung komplementärer Charakterisierungsmethoden. Ziel dieser Arbeit war der Einbau von S-, N- und P-haltigen funktionellen Gruppen auf mehrwandigen CNTs, um gezielt Oberflächen mit sauren und basischen Zentren zu generieren. Die Art, Menge und thermische Stabilität der funktionellen Gruppen wurde vorwiegend mittels TPD, XPS, Mikrokalorimetrie und Elementaranalyse aufgeklärt. Die Säure-Base-Eigenschaften der Oberflächen wurden komplementär sowohl mittels pH-Titration in wässriger Phase als auch durch die sauer- bzw. basisch katalysierte Umsetzung von 2-Propanol in der Gasphase als sensitive Sondenreaktion bestimmt. TPO gab Aufschluss über den Einfluss der Heteroatome auf die oxidative Beständigkeit der CNTs. Zunächst gelang die Seitenwandfunktionalisierung der CNTs mit Sulfonsäuregruppen mit Hilfe einer Diazotierung von Sulfanilsäure in o-Dichlorbenzol und Wasser. TPD- Experimente bestätigen eine thermische Stabilität der Gruppen bis 250 °C. Sowohl die pH-Titration als auch eine hohe Propylenselektivität in der Umsetzung von 2-Propanol beweisen die sauren Oberflächeneigenschaften. Eine Desaktivierung kann bei Durchführung der Reaktion unterhalb von 200 °C vermieden werden. Die Menge an sauren Zentren korreliert hierbei mit der Konzentration an S in den Proben und es konnte herausgestellt werden, dass das Lösungsmittel Wasser gegenüber o-Dichlorbenzol einen höheren S-Einbau begünstigt. Die Darstellung N-funktionalisierter CNTs gelang mittels Aminierung in 50% NH3/Ar- Atmosphäre von O-funktionalisierten CNTs bei verschiedenen Temperaturen. TPD- und XPS-Analysen ergaben die Anwesenheit von vorwiegend Imiden und Lactamen nach Behandlung bei 300 °C und pyrrolischen N nach Funktionalisierung bei 500 °C. Eine Aminierung bei 700 °C führt gezielt zu überwiegend pyridinischen N. Während der N- Gehalt mit zunehmender Behandlungstemperatur leicht sinkt, steigt die Basizität der Oberflächen drastisch
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