«Shape Selective Conversion of Methanol to Hydrocarbons over Uni-Dimensional 10-ring Zeolites Dissertation for the degree of Philosophiae Doctor ...»
Shape Selective Conversion of Methanol to
Hydrocarbons over Uni-Dimensional 10-ring Zeolites
Dissertation for the degree of
Shewangizaw Teketel Forsido
DEPARTMENT OF CHEMISTRY
Faculty of mathematics and natural sciences
UNIVERSITY OF OSLO
© Shewangizaw Teketel Forsido, 2013
Series of dissertations submitted to the
Faculty of Mathematics and Natural Sciences, University of Oslo No. 1321 ISSN 1501-7710 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission.
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Preface This Ph.D. thesis is submitted to the Department of Chemistry, Faculty of Mathematics and Natural Sciences, University of Oslo (UiO). My employment at UiO was from August 2009 to February 2013, a total of six months of the time was spent at the laboratories of Haldor Tøpsoe A/S, Denmark. The work was financed by the Innovative Natural Gas Processes and Products (inGAP), Centre of Research-based Innovation, which receives financial support from the Norwegian Research Council under Contract No. 174893.
Associate Professor Stian Svelle (UiO) has been my principal supervisor. Professor Unni Olsbye (UiO), Professor Karl Petter Lillerud (UiO) and Doctor Pablo Beato (Haldor Topsøe) were my subsidiary supervisors. Stian is greatly acknowledged for his close guidance and fruitful discussions throughout the Ph.D. work. Pablo is greatly acknowledged for his guidance and great time during my industrial traineeship in Denmark. Unni and Karl Petter are greatly acknowledged for their contribution through fruitful discussions.
The work behind paper I was carried out during my master degree, under supervision of Professor Unni Olsbye. However, since it is relevant for the Ph.D. work, I have included it in this thesis.
I would like to thank my colleagues at the catalysis group for the very nice working environment. I want to particularly mention Wegard Skistad for our discussions, and Marius W. Erichsen for reading the draft of this thesis. Special thanks to people outside the catalysis group: Marit, Endrias, Stian and friend in OiC for the good company. Finally, my parents Ato Teketel Forsido and W/O Zenebech Banjaw are greatly acknowledged for their encouragement and support.
Shewangizaw Teketel Forsido December, 2012 Table of Contents List of papers
Paper I: Shape-Selective Conversion of Methanol to Hydrocarbons Over 10-Ring Unidirectional-Channel Acidic H-ZSM-22. S. Teketel, S. Svelle, K. P. Lillerud, U.
Olsbye. ChemCatChem 1 (2009) 78-81 Paper II: Selectivity Control through Fundamental Mechanistic Insight in the Conversion of Methanol to Hydrocarbons over Zeolites. S. Teketel, U. Olsbye, K. P. Lillerud, P. Beato, S.
Svelle. Microporous Mesoporous Mater. 136 (2010) 33-41.
Paper III: Shape Selectivity in the Conversion of Methanol to Hydrocarbons: The Catalytic Performance of One-Dimensional 10-Ring Zeolites: ZSM-22, ZSM-23, ZSM-48, and EU-1. S.
Teketel, W. Skistad, S. Benard, U. Olsbye, K. P. Lillerud, P. Beato, S. Svelle. ACS Catal. 2 (2012) 26-37 Paper IV: Morphology Induced Shape Selectivity in Zeolite Catalysis. S. Teketel, L. F.
Lundegaard, U. Olsbye, K. P. Lillerud, P. Beato, S. Svelle. To be submitted (2012).
Paper V: Co-conversion of Methanol and Light Alkenes to Hydrocarbons over Acidic Zeolite Catalyst H-ZSM-22: Simulated Recycle of Non-Gasoline Products. S. Teketel, U. Olsbye, K.
P. Lillerud, P. Beato, S. Svelle. In Preparation, (2012).
Paper I: The author synthesized, characterized the zeolite, and performed all the catalytic tests. The author contributed to the planning of the experiments, interpretation of the results and preparation of the manuscript.
Paper II: The author synthesized, characterized the zeolite, and performed all the catalytic tests. The author contributed to the planning of the experiments, interpretation of the results and preparation of the manuscript.
Paper III: The author contributed to the synthesis and characterization of the zeolites, and performed all the catalytic tests. The author was involved in the planning of the experiments, interpretation of the results and preparation of the manuscript. EU-1 zeolite was synthesized by Wegard Skistad, and ZSM-48 was synthesized by Wegard Skistad in collaboration with Sandrine Benard.
Paper IV: The author synthesized, characterized the zeolite and performed all the catalytic tests. The author contributed to the planning of the experiments, interpretation of the results and preparation of the manuscript. TEM and XRD analyses of the catalyst were performed by Lars F. Lundegaard.
Paper V: The author has performed all the catalytic tests. The author contributed to the planning of the experiments, interpretation of the results, and preparation of the manuscript.
I. Conversion of Methanol to Hydrocarbons over 10-ring Unidirectional Acidic HZSM-22. S. Teketel, S. Svelle, K. P. Lillerud, P. Beato, U. Olsbye. Norwegian Catalysis Symposium, Trondheim, Norway, 2009/11/30 (Oral presentation) II. Production of Non-Aromatic Gasoline from Methanol over Unidirectional 10-ring Zeolite Catalysts. S. Teketel, W. Skistad, S. Benard, U. Olsbye, K. P. Lillerud, P.
Beato, S. Svelle. EuropaCat, Glasgow, Scotland 2011/08/28 (Poster presentation) III. Shape Selectivity in the Conversion of Methanol to Hydrocarbons: the Catalytic Performance of 1D 10-ring Zeolite: ZSM-22, ZSM-23, ZSM-48 and EU-1. S.
Teketel, W. Skistad, S. Benard, U. Olsbye, K. P. Lillerud, P. Beato, S. Svelle.
Norwegian Catalysis Symposium, Lillestrøm, Norway, 2011/09/28 (Oral presentation) Patent application I. Catalyst for the Conversion of Oxygenates to Olefins and a Process for Preparing Said Catalyst. S. Teketel, S. Svelle and P. Beato, Danish Patent Office, Reference number: 1037 DK BECH/ANKR, Copenhagen, Denmark, 2011/07/22.
I. Interplay Between Nanoscale Reactivity and Bulk Performance of H-ZSM-5 Catalysts during the Methanol to Hydrocarbons Reaction. L. R. Aramburo, S.
Teketel, S. Svelle, S. R. Bare, B. Arstad, H. W. Zandbergen, U. Olsbye, F. M. F. de Groot, B. M. Weckhuysen. Submitted to J. Catal. (2012).
II. Large Zeolite H-ZSM-5 Crystals as Models for the Methanol to Hydrocarbons Process: Bridging the Gap between Individual Crystals and Powdered Catyalysts, J.
P. Hafmann, D. Mores, L. R. Aramburo, S. Teketel, M. Rohnke, J. Janek, U. Olsbye, B. M. Weckhuysen. Submitted to Chem. A Rurop. J. (2012) III. Single-Event MicroKinetics (SEMK) for Methanol to Hydrocarbons (MTH) on HZSM-23, P. Kumar, J. W. Thybaut, S. Teketel, S. Svelle, U. Olsbye, P. Beato, G. B.
Marin. Submitted to Catal. Today, (2012).
IV. Combined Operando Spectroscopy and Ex-situ Chemical Analysis Tools for Mechanistic Investigations of the Methanol to Hydrocarbon Reaction, S. Teketel, F.
Bonino, W. Skistad, U. Olsbye, K. P. Lillerud, S. Bordiga, S. Svelle, P. Beat.
Submitted to Catal. Today, (2012).
1.1. Catalysis in general In order for a chemical reaction to occur, the reactant molecules must overcome an energy barrier. A catalyst is a substance that accelerates the progress of a chemical reaction towards equilibrium, and allows the reaction to occur with a low energy barrier. A catalyst does not change the thermodynamics (energy difference between starting materials and products) and the equilibrium concentrations of a reaction. Figure 1.1 displays potential energy diagrams of catalytic and non-catalytic reactions. The non-catalytic reaction path goes through a much higher energy barrier, full curve .
Figure 1.1: Potential energy diagram for non-catalytic path (full curve) catalytic (dotted curve).
The catalytic path is more complex but thermodynamically favorable, dotted curve. It involves adsorption of the reactants on to the active sites, reactions leading to product formation, and finally desorption of the product from the catalyst. In addition to lowering of the energy barrier of chemical reactions, catalysts increase the number of collisions between reactant molecules by offering adsorption sites . Catalysis is divided in to three subdisciplines: homogeneous, heterogeneous and biocatalysis (enzymatic) catalysis. In homogeneous catalysis, reactants, products and the catalyst are in one phase, usually in a liquid phase. In heterogeneous catalysis, the reactant, products and the catalyst are in different phases. Usually, the catalyst is a solid while the reactant and product are gases or liquids.
Biocatalysis is based on enzymes, proteins which are highly specific to certain substrates and products.
In the last century catalysis was aimed at increasing turnover rates, but during the 20th century, catalysis evolved into understanding and controlling selectivity [2-4]. Therefore in this century, in addition to increased turnover rates, catalysts are required to provide selectivity towards desired products. In such catalytic processes, raw materials are used more efficiently and waste production is minimized. Most chemical industries rely on catalysts and about 85-90 % of all petrochemical products are made in catalytic processes .
Zeolites are crystalline aluminosilicates with a three-dimensional framework that consists of nanometer-sized channels and cages, giving a high porosity and a large surface area to the material . The three-dimensional framework of zeolites is constructed from corner shared tetrahedral (T-atoms) of silicon and aluminum, bridged with oxygen atoms. The dimensions of zeolite channels, channel intersections and/or cages are typically less than 2 nm. The International Union of Pure and Applied Chemistry (IUPAC) classifies porous materials as mirocoporous, mesoporous and macroporous based on sizes 2 nm, 2-50 nm and 50 nm respectively , therefore zeolites are referred to as microporous materials. Figure 1.2 illustrates examples of selected zeolite structures along with their pore systems. The zeolite pore size is mainly determined by the number of T-atoms defining the entrance (ring-size) to the interior of the crystal, for example in Figure 1.2 the pore size of ZSM-22 (10-ring) is smaller than that of ZSM-12 (12-ring). Accordingly, zeolites are classified as having small, medium, large, and extra-large pore structures for pore windows delimited by 8, 10, 12, and more than 12 T-atoms, respectively . The pores in zeolites can be one-dimensional (Figure 1.2, ZSM-12 and ZSM-22), two-dimensional (for example MCM-22 ), or threedimensional (Figure 1.2, ZSM-5 and Faujasite). The pore sizes of zeolites are in the range of the molecular diameters of organic compounds, and only molecules with smaller free diameter than the zeolite pores can have access to the interior of the zeolite crystal. Due to such ability to sort molecules based on sizes, zeolites are often described as molecular sieves .
Figure 1.2: Structures of zeolites (from top to bottom: faujasite or zeolite X, Y; zeolite ZSM-12; zeolite ZSM-5 or silicalite-1; zeolite ZSM-22) and their micropore system.
Adapted from Ref.  The first naturally occurring zeolite was recognized in 1756 by a Swedish mineralogist, Cronstedt . He named it “zeolite” from the Greek words “zein” (boiling) and “lithos” (stone) because the new material released large amounts of steam and water upon heating. Currently there are nearly 200 zeolites maintained in the database of the International Zeolite Association (IZA) . All zeolite structures are given a three capital letters code, following the rule set by an IUPAC Commission on Zeolite Nomenclature [12, 13]. About one fifth of the zeolites in the IZA database are naturally occurring, and the rest are synthetic zeolites made in laboratories. Furthermore, computer prediction of hypothetical zeolites shows several million possible structures, of which 450000 are potentially stable when their calculated lattice energies are compared with those of known zeolite structures .
Hypothetical zeolite structures are also maintained in an online databases [14, 15].
The synthesis of zeolites is usually carried out under hydrothermal conditions, from sources of silicon, aluminum dissolved in aqueous solution of alkali hydroxide and structure directing agent (SDA), illustrated in Figure 1.3. Zeolites are metastable and the final synthesis product is determined by factors such as nature and concentrations of reactants and synthesis conditions (temperature, crystallization time, and pH). The hydrothermal synthesis of zeolites is often carried out in autoclave at elevated temperature and autogenous pressure.
Crystallization from solution generally occurs via the sequential steps of nucleation of the phase(s), dictated by the composition of the solution, followed by growth of the nuclei to larger sizes by incorporation of solute from the solution . The final crystal size is a function of the ratio between rate of nucleation and rate of growth of the nuclei . The zeolite crystallization process is dependent on a number of parameters such as: ageing of the synthesis gel , solubility of silicon , crystallization temperature , and addition of seed crystals .
Figure 1.3: Illustration of hydrothermal zeolite synthesis. Adapted from Ref. 
Crystal sizes play important roles in application of zeolites as catalyst. For example, catalyst effectiveness is larger for smaller crystals, but filtration and recovery of very small crystals can be practically a challenge. Shape selective catalysis requires larger crystals (see section 1.3.), but deactivation can be more severe and regeneration of used catalyst can be more difficult for larger crystal .