https://theses.gla.ac.uk/ Theses Digitisation: https://www.gla.ac.uk/myglasgow/research/enlighten/theses/digitisation/ This is a digitised version of the original print thesis. Copyright and moral rights for this work are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This work cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Enlighten: Theses https://theses.gla.ac.uk/ [email protected] RADIOTRACER STUDIES OF ADSORPTION ON METHANOL SYNTHESIS CATALYSTS THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY OF THE UNIVERSITY OF GLASGOW BY SUSAN EVITT, B.Sc. OCTOBER, 1986 ProQuest Number: 10991909 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. uest ProQuest 10991909 Published by ProQuest LLO (2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLO. ProQuest LLO. 789 East Eisenhower Parkway P.Q. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 I dedicate this work, to my husband, Thomas Andrew Kinnaird, for his patience and encouragement over the past three years. ACKNOWLEDGEMENTS I would like to express my sincere thanks to Dr. G. Webb, my supervisor, and to Mr. G.C. Chinchen, my industrial supervisor, for proposing the topic for the thesis and for their advice and co-operation over the last three years. I am indebted to Mr. R.A. Hadden and the rest of my colleagues in surface chemistry for their encouragement and advice and to Mr. T. Boyle and Mr. R. Kennedy for their technical assistance. Thanks are also due to Mr. C.R. Plant and Mr. M. Shann for their assistance during my industrial visit and to both I.e.I. Agricultural Division and the Science and Engineering Research Council for the award of a C.A.S.E. Studentship. I gratefully acknowledge the assistance of Dr. D. Parker (Physics and Radioisotopes Group, I.C.I. Petrochemicals and Plastics Division) and for the provision of radioactive materials used in this study. SUMMARY The adsorption of carbon dioxide and carbon monoxide on a Cu/ZnO/AlgOg methanol synthesis catalyst and the ZnO and AlgOg components of this catalyst, at ambient temperature, has been investigated using a [ 1A-C]radiotracer technique. Before adsorption of the various gases, the catalysts were activated in a stream of 5% hydrogen in argon at 463K. The relative strengths of adsorption of carbon dioxide and carbon monoxide, on the various catalysts, have been investigated by evacuation and molecular exchange experiments. Exchange between one of the [14-C]labe11ed carbon oxides pre-adsorbed on each of the catalysts and the other non labelled carbon oxide in the gas phase, together with adsorption measurements for each of the [14-C]carbon oxides after admission of the other non labelled gas, was used to examine the degree of competitive adsorption between the two adsorbates. The effects, both separate and combined, of oxygen (from nitrous oxide) adsorbed on the copper surface and of hydrogen on the adsorption of carbon dioxide and carbon monoxide on Cu/ZnO/Al^O^, have also been examined using both the radiotracer method and a microreactor system coupled to a mass spectrometer. It has been shown that, carbon dioxide adsorbs both weakly and relatively strongly on each of the components of the catalyst. On the copper component, carbon dioxide dissociates at high energy sites to give adsorbed carbon monoxide and surface oxygen. This adsorbed carbon monoxide is different to that from the species obtained by adsorption of gaseous carbon monoxide in that it is strongly adsorbed and perhaps multiply bonded to the surface. Further slow adsorption of carbon dioxide takes place with oxygen atoms, formed by the dissociative adsorption of carbon dioxide, as well as with surface oxygen remaining after the reduction process to form a carbonate species. Similarly, a slow adsorption of carbon dioxide occurs on the support, forming a more strongly adsorbed species. A limited amount of surface oxygen on the copper component, does not affect the amount of carbon dioxide adsorbed on the catalyst, although its strength of adsorption is increased. In sharp contrast, when the copper component is fully oxidised, sites for the adsorption of carbon dioxide are initially blocked, adsorption of this gas on fully oxidised copper being a very slow process. Although hydrogen has little effect on the adsorption of carbon dioxide on reduced Cu/ZnO/Al^O^, complex formation takes place between carbon dioxide and hydrogen adsorbed on partially oxidised Cu/ZnO/Al^O^. Hydrogen adsorbs at Cu'*’ - Cu° sites to form hydroxyl groups which react with carbon dioxide possibly to form surface formate species. In sharp contrast with carbon dioxide, carbon monoxide adsorbs, almost exclusively, on the copper component of the catalyst, where it is adsorbed relatively weakly. Although CONTENTS Page ACKNOWLEDGEMENTS SUMMARY CHAPTER ONE INTRODUCTION 1.1 Background to the Catalytic Synthesis 1 of Methanol 1.1.1 Background to the Role of Copper in 3 Methanol Synthesis Catalysts 1.1.2 Background to the Role of ZnO in 5 Methanol Synthesis Catalysts 1.1.3 Background to the Role of Al^Og in 7 Methanol Synthesis Catalysts 1.1.4 The Active Component(s) of the 1 1 Cu/ZnO/Al203 "Low Pressure" Methanol Synthesis Catalyst 1 . 2 The Adsorption of Carbon Monoxide, 22 Carbon Dioxide and Hydrogen on Cu/ZnO/Al203 and the Role of Each Gas in the Synthesis of Methanol CHAPTER TWO OBJECTIVES OF THE PRESENT WORK 53 CHAPTER THREE EXPERIMENTAL 3. 1 The Vacuum System 54 3.2 The Geiger-Muller System 56 3.3 The Pressure Transducer 58 3.4 The Gas Chromatography System 58 3.5 Catalysts 60 3.5.1 Preparation of a High Surface Area ZnO o2 3.5.2 Preparation of 80% Cu/Al^O^ 62 3.6 Materials 63 3.6.1 Preparation of [14-C]Carbon Monoxide 64 3.7 Experimental Procedure 65 3.7.1 Catalyst Activation 65 3.7.2 Preparation of Oxidised Cu/ZnO/Al^O^ 65 Catalyst Samples 3.7.2 1 Preparation of Fully Oxidised 66 Cu/ZnO/Al^O^ Samples 3.7.2 2 Preparation of Partially Oxidised 67 Cu/ZnO/Al^O^ Samples Page 3 .7.3 Corrections to the Observed 67 Count Rates 3 .7.4 Adsorption Isotherms 69 3.8 Adsorption Studies in a Flow System 70 3.8.1 Experimental 70 3.8. 1.1 Materials 71 3.8.2 Experimental Procedure 71 3.8.2.1 Catalyst Activation 71 3.8.2.2 Measurement of Copper Surface Area 72 CHAPTER FOUR RESULTS 4.1 Adsorption of [14-C]Carbon Dioxide on 73 Reduced Cu/ZnO/Al^O^ 4.1.1 Adsorption of [14-C]Carbon Dioxide on 76 Unreduced Cu/ZnO/Al^O^ 4.1.2 The Reversibility of Adsorption of 76 Carbon Dioxide on Reduced Cu/ZnO/Al^O^ 4.1.3 Successive Adsorptions/Evacuations of 79 [14-C]Carbon Dioxide on the Same Reduced Cu/ZnO/Al^O^ Catalyst Sample 4.1.4 The Effects of Hydrogen on the 79 Adsorption of Carbon Dioxide on Reduced Cu/ZnO/Al^O^ 4 .1.5 Adsorption of [14-C]Carbon Dioxide on 80 Reduced Cu/ZnO/AlpO_ Over a Long Time Period 4.2 Adsorption of [14-C]Carbon Monoxide 82 on Reduced Cu/ZnO/Al^O^ 4.2.1 Adsorption of [14-C]Carbon Monoxide 82 on Unreduced Cu/ZnO/Al^O^ 4.2.2 The Reversibility of Adsorption of 82 Carbon Monoxide on Reduced Cu/ZnO/Al^O^ 4.2.3 Successive Adsorptions/Evacuations of 85 [14-C]Carbon Monoxide on the Same Reduced Cu/ZnO/Al^O^ Catalyst Sample 4.2.4 The Effects of Hydrogen on the 85 Adsorption of Carbon Monoxide on Reduced Cu/ZnO/Al^O^ 4 .2.5 Adsorption of [14-C]Carbon Monoxide on 86 Reduced Cu/ZnO/AlpO^ Over a Long Time Period 4.3 Co-Adsorption of Carbon Dioxide, and 86 Carbon Monoxide on Reduced Cu/ZnO/Al^O^ Page 4.3.1 Adsorption of [14-C]Carbon Dioxide 86 Followed by the Adsorption of [14-C]Carbon Monoxide on Cu/ZnO/Al^O^ 4.3.2 Adsorption of [14-C]Carbon Monoxide 87 Followed by the Adsorption of [14-C] Carbon Dioxide on Reduced Cu/ZnO/Al^O^ 4.3.3 Adsorption of [14-C]Carbon Dioxide 87 on a [12-C]Carbon Monoxide Precovered Cu/ZnO/Al^O^ Surface 4.3.4 Adsorption of [14-C]Carbon Monoxide 87 on a [12-C]Carbon Dioxide Precovered Cu/ZnO/AlgOq Surface 4.3.5 Exchange Between Carbon Dioxide 88 Adsorbed on Cu/ZnO/Al^O^ and Gas Phase Carbon Monoxide 4.3.6 Exchange Between Carbon Monoxide 90 Adsorbed on Cu/ZnO/Al^O^ and Gas Phase Carbon Dioxide 4.4 Adsorption of [14-C]Carbon Dioxide 91 and [14-C]Carbon Monoxide on Cu/Al^O^ 4.4.1 The Reversibility of Adsorption of 91 Carbon Dioxide and Carbon Monoxide on Cu/AlgOg 4.5 Adsorption of [14-C]Carbon Dioxide 93 and [14-C]Carbon Monoxide on ZnO - A 4.5.1 The Reversibility of Adsorption of 93 Carbon Dioxide and Carbon Monoxide on ZnO - A 4.5.2 The Effects of Hydrogen on the 96 Adsorption of Carbon Dioxide and Carbon Monoxide on ZnO - A 4.5.3 Adsorption of [14-C]Carbon Dioxide 96 on ZnO - A Over a Long Time Period 4.5.4 Co-Adsorption of Carbon Dioxide and 97 Carbon Monoxide on ZnO - A 4.5.4.1 Adsorption of [14-C]Carbon Dioxide 97 on ZnO - A Followed by the Adsorption of [14-C]Carbon Monoxide and the Adsorption of [14-C]Carbon Monoxide on ZnO -