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Reaction of Glucose Catalyzed by Framework and Extraframework Tin Sites in Zeolite Beta

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Reaction of Glucose Catalyzed by Framework and Extraframework Tin Sites in Zeolite Beta Reaction of Glucose Catalyzed by Framework and Extraframework Tin Sites in Zeolite Beta Thesis by Ricardo Bermejo-Deval In Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2014 (Defended 12 May 2014) ii 2014 Ricardo Bermejo-Deval All Rights Reserved iii ACKNOWLEDGEMENTS The past years at Caltech have been one of the most challenging periods of my life, learning to be a better person and being part of the world of science. I feel privileged to have interacted with such talented and inspiring colleagues and scientists, as well as those I have disagreed with. The variety of people I have encountered and the experiences I have gathered have helped me to gain scholarship, wisdom, confidence and critical thinking, as much as to become an open-minded person to any opinion or people. First and foremost, I am very grateful to my advisor and mentor, Professor Mark E. Davis, for his financial, scientific and personal support. I appreciate his patience, flexibility, advice and scientific discussions, helping me to grow and mature scientifically. I would like to thank the thesis committee Professors Richard Flagan, Jay Labinger and Theodor Agapie, for their discussions and kindness. I appreciate everyone in the Davis group for helping me in the lab throughout these years. Special thanks to Yasho for helping me get started in the lab, to Bingjun and Raj for scientific advice, and to Marat for helpful talks. I am also very thankful to Sonjong Hwang for SS NMR, David Vandervelde for NMR and Mona Shahgholi for mass spectrometry. In addition, I would like to express my gratitude to the people at Chevron R&D at Richmond, for conceding me an internship with them during July-October 2012, especially to C.Y. Chen. I would like to thank all of my classmates, professors and mentors in my home city Valencia, Spain, who believed and trusted in me to pursue a PhD at Caltech. I am greatly indebted to Professors Carmen Gabaldon and Paula Marzal, for mentoring me during my undergraduate degree and research fellowship. I am greatly honored to be iv guided in my research career by Professor Avelino Corma, who has aided with both scientific and personal advice. I would also like to express my gratitude to “la Caixa” fellowship program for paying part of my PhD studies, as well as granting me the opportunity to meet great people. I feel truly fortunate to have met and become friends with a great number of people throughout these years: Marilena, Matt Coggon, Matt Shanner, Vanessa, Kathy, Carlos, Alejandro, Pablo & others… I feel really lucky to have shared such great times with the Caltech Masters Swimteam and their friends: Andrew, Evelyn, Sean, Tobias, AJ and Dubi. I will never forget the support and friendship that Charlie Slominski and Matt Lalli have provided me with, during both good and bad times. To all of you, thank you. Last but not least, I would like to express my deepest gratitude to my family who have always supported and believed in my goals. To my dad, Toni, for being patient in all aspects of my life; to my brother, John, for providing me with laughter and joy since the day he was born; and to my mum, Helen, for guiding me in my life and pushing me to become the person I am. v ABSTRACT The isomerization of glucose into fructose is a large-scale reaction for the production of high-fructose corn syrup, and is now being considered as an intermediate step in the possible route of biomass conversion into fuels and chemicals. Recently, it has been shown that a hydrophobic, large pore, silica molecular sieve having the zeolite beta structure and containing framework Sn4+ (Sn-Beta) is able to isomerize glucose into fructose in aqueous media. Here, I have investigated how this catalyst converts glucose to fructose and show that it is analogous to that achieved with metalloenzymes. Specifically, glucose partitions into the molecular sieve in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center (framework Sn4+), isomerizes into the acyclic form of fructose and finally ring closes to yield the furanose product. Akin to the metalloenzyme, the isomerization step proceeds by intramolecular hydride transfer from C2 to C1. Extraframework tin oxides located within hydrophobic channels of the molecular sieve that exclude liquid water can also isomerize glucose to fructose in aqueous media, but do so through a base-catalyzed proton abstraction mechanism. Extraframework tin oxide particles located at the external surface of the molecular sieve crystals or on amorphous silica supports are not active in aqueous media but are able to perform the isomerization in methanol by a base-catalyzed proton abstraction mechanism. Post-synthetic exchange of Na+ with Sn-Beta alters the glucose reaction pathway from the 1,2 intramolecular hydrogen shift (isomerization) to produce fructose towards the 1,2 intramolecular carbon shift (epimerization) that forms mannose. Na+ remains exchanged onto silanol groups during reaction in methanol solvent, leading to a near complete shift in selectivity towards glucose epimerization to mannose. In contrast, vi decationation occurs during reaction in aqueous solutions and gradually increases the reaction selectivity to isomerization at the expense of epimerization. Decationation and concomitant changes in selectivity can be eliminated by addition of NaCl to the aqueous reaction solution. Thus, framework tin sites with a proximal silanol group are the active sites for the 1, 2 intramolecular hydride shift in the isomerization of glucose to fructose, while these sites with Na-exchanged silanol group are the active sites for the 1, 2 intramolecular carbon shift in epimerization of glucose to mannose. vii TABLE OF CONTENTS Acknowledgements……………………...……………………………………………….iii Abstract…………………………………………………………………………………....v Table of Contents………………………………………………………………………..vii List of Figures…………………………………………………………………………...xii List of Tables…………………………………………………………………………..xxiii Chapter 1: Introduction and Thesis Organization .............................................................2 1. Biomass Conversion into Biofuels and Fine Chemicals .................................................2 1.1 Biomass Components ...................................................................................................................... 2 2.2 Biomass Hydrolysis .......................................................................................................................... 3 2.3 Biomass Applications ....................................................................................................................... 4 2. Introduction to Zeolites, Lewis Acids and Zeolite Sn-Beta ............................................7 2.2 Introduction to Zeolites and Molecular Sieves............................................................................. 7 2.3 Lewis Acids ................................................................................................................................... 9 2.4 Microporous and Mesoporous Lewis Acids ............................................................................... 11 2.5 Zeolite Sn-Beta ........................................................................................................................... 13 3. Motivation and Thesis Organization ......................................................................... 17 4. References ............................................................................................................... 20 Chapter 2 : The Glucose Isomerization into Fructose Reaction Pathway wih Sn-Beta .... 26 1. Introduction ............................................................................................................ 26 2. Results and Discussion ............................................................................................. 31 viii 2.1 The Ring Opening ........................................................................................................................... 31 2.2 Isomerization Step ......................................................................................................................... 35 2.3 Reaction Centers with Sn or Ti Containing Zeolite ......................................................................... 37 2.4 The Formation of Mannose ........................................................................................................... 43 3. Conclusion ............................................................................................................... 52 4. Experimental and Additional Figures ........................................................................ 53 4.1 Synthesis of Ti-Beta, TS-1, Sn-Beta and CH3-Sn-Beta ..................................................................... 53 4.2 Isomerization Reactions ................................................................................................................. 56 4.3 Glucose Adsorption Experiments ................................................................................................... 56 4.4 Characterization ............................................................................................................................. 57 4.5 Additional Figures .......................................................................................................................... 58 5. Computational Studies ............................................................................................
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