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Preparation and Characterisation of Vanadium Phosphorus Oxide

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Preparation and Characterisation of Vanadium Phosphorus Oxide Cardiff CARDIFF UNIVERSTY UNIVERSITY Department of Chemistry |HPRIFYSGOL j CAeRDY£> Preparation and Characterisation of Vanadium Phosphorus Oxide Catalysts for Butane Oxidation to Maleic Anhydride Thesis submitted in accordance with the requirements of the University of Cardiff for the degree of Doctor of Philosophy By Raja Lafi AL-Otaibi January 2010 UMI Number: U571273 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U571273 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 >11 0 ^ 4 .>11 -Oil *-4 In The Name Of Allah. The Most Beneficent. The Most Merciful Declaration This work has not previously been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree S ig n ed .................. ■...;............ .............................. (Candidate) D ate................ ........................................................ Statement 1 This thesis is the result of my own investigation, expect where otherwise stated. Other sources are acknowledged by giving explicit references. A bibliography is attached in the thesis. Signed .................................................................... (Candidate) D ate................... .................................................... Statement 1 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisation. Signed (Candidate) For my parents h i Acknowledgments I would like to begin with by thanking Allah the almighty, for his bounties upon us and for his assistance in my studies and without him, nothing is possible. I am deeply grateful to my supervisor, Professor Graham Hutchings, for his guidance, teachings and constant support. I wish to thankfully acknowledge Dr. Jonathan Bartley for his advice and unlimited support on resolving technical problems and discussing experimental data. I am also very thankful to Dr. Nicholas Dummer for his suggestions and corrections during the writing of this thesis. Thanks are due to my employer, King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia for financial support. Special thanks to my Friend Salem Bawaked and all my friends in lab 1.88 and 1.96 for their help during my study in Cardiff. Meanwhile I have to thank the Leigh University, USA for getting the TEM images for my study. To my beloved parents, you know how special you are how much you are loved. Thanks for your prays for me and thanks for being there at the other end of the phone... Finally, I express my deep thanks to my wife for being here with me during my study period, without you I do not think I could have made it. IV Abstract The selective oxidation of n-butane to maleic anhydride catalysed with vanadium phosphates continues to receive significant research attention due to its importance in academic and industrial sectors. The catalytic performance of vanadium phosphates is highly dependent on the method of preparation of the catalyst precursors VOHPO4.O.5H2O. The morphology and surface area of the precursor are factors of importance to achieve good catalytic results. This thesis aims the study of new preparative routes to get catalyst precursors VOHPO4.O.5H2O with good catalytic performance for the selective oxidation of n-butane to maleic anhydride. The use of octane as co-solvent shows a significant effect on the morphology of VOHPO4 .O.5 H2O precursor which was prepared via three different routes. The reaction of VOPO 4 .2 H2O with octane solvent shows the possibility of the intercalation of the octane solvent between the layers of VOPO 4 .2 H2O. This can lead to the formation of VOHPO4.O.5 H2O precursors with a new morphology after the reduction step using 1- butanol. In addition, the use of octane as co-solvent with 1-butanol leads to the formation of VOHPO 4.O.5 H2O with a different XRD pattern and new morphology. Testing these samples shows that the samples with a rosette morphology exhibit the highest conversion and selectivity compared with the new materials prepared. A study of the factors influencing the preparation of vanadium phosphates during the VPD type alcohol reduction of VOPO 4 2 H 2O. In this thesis, we demonstrate that the use of seed crystals of vanadium phosphate can have a dramatic influence on the morphology and phase identity of the precursor materials. VOHPO 4 O.5 H2O was prepared from VOPO 4 2 H2O using 1- and 3-octanol, 2-butanol and 2-methyl-1-propanol as both solvent and reducing agent. With 1 -octanol the reaction temperature was found to be crucial in obtaining a high yield of the precursor phase, and at temperatures >160 °C a solution, containing V4+ ions formed in preference to VOHPO 4 O.5 H2O. However, VOHPO4 O.5 H2O formation can be achieved by the addition of a small amount of V-P- O material as seeds if carrying out the reduction process above this temperature. In contrast, when 3-octanol is used, VO(H 2PC>4)2 is formed solely, but in the presence of a V-P-0 seed significant amounts of VOHPO 4 O.5 H2O can also be formed.. Studying the reaction time online shows that V 0 (H2P 0 4 ) 2 could be transformed to VOHPO 4.O.5 H2O, which has been attempted previously without success. Finally, testing these samples under reaction conditions shows that they demonstrate high selectivity toward MA and good conversion compared to V 0 (H2P0 4 ) 2 Vanadium phosphate catalysts have successfully been prepared in aqueous media using hydrogen. The catalysts precursors obtained were poorly crystalline VOHPO4.0.5H2O and a minor amount of an impurity detected by a reflection in the XRD pattern. V Activating these materials for n-butane oxidation show low selectivity of MA (5%), which could be attributed to the presence of V(V) phases after activation. VI Table of contents Declaration ............................................................................................................................... jj Dediction .................................................................................................................................. jjj Acknowledgments ................................................................................................................... jy Abstract..................................................................................................................................... y Table of contents ..................................................................................................................... y jj CHAPTER 1: Introduction 1.1 Introduction ....................................................................................................................... I 1.2 Reaction M echanism ....................................................................................................... 2 1.3 The active catalyst............................................................................................................ g 1.4 Activation of catalyst precursors .................................................................................. ^ 2 1.4.1 Activation procedures ..................................................................................... 12 1.4.2 Structural transformations .............................................................................. 13 1.5 The phosphorus to vanadium ratio of the catalyst .................................................... 1 3 1.6 Promoted catalysts .......................................................................................................... 1 ^ 1.7 Preparation of catalyst precursors VOHPO 4 .O.5 H2O .............................................. 20 1.8 Preparation of other VPO phases .................................................................................. 23 1.8.1 Preparation of V 0 (H2 P0 4 ) 2 ........................................................................... 2 3 1.8.2 Preparation of VOPO 4 phases....................................................................... 24 1.9 Crystal structures of vanadium phosphate phases.................................................... 25 VII 1.10 New preparative routes ................................................................................................ 2 9 1.11 The aims of this study................................................................................. 1.12 References ....................................................................................................................... 3 3 CHAPTER 2: Experimental details .......................................................................... 3 g 2.1 Catalyst Preparation ........................................................................................................ 3 g 2.1.1 Standard V-P-0 catalysts ............................................................................................ 3 g 2.1.1.1 Preparation of VOPO 4.2 H2O ..................................................................... 3 g 2.1.1.2 Preparation of VOHPO 4.O.5 H
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