Influences of MOISTURE on ROM TEMPERATURE CO OXIDATION over AuBN catalysts

Influences of MOISTURE on ROOM TEMPERATURE CO OXIDATION over Au/BN catalysts Student: Tuyet-Mai Tran-Thuy Supervisor: Shawn D Lin July, 2017 Taipei City, Taiwan Abstract Metal oxide supported gold catalysts readily catalyze CO oxidation at sub-ambient temperature, wherein moisture can influence the activity typically with a volcano-shape dependence The abundant OH density on metal oxide surface hinders the study of how moisture may influence the CO oxidation over Au catalysts In this work, we use hexagonal Boron Nitride (h-BN), a hydrophobic material, as the support for gold catalyst to study room temperature CO oxidation with various partial pressure of water (PH2O) A deposition method was conducted for preparing 1wt%Au/BN Two commercial h-BN supports are compared and the effect of pretreatment conditions is examined for understanding the observed moistureenhanced catalytic activity The first strategy of this work is using spectroscopic methods to explore roles of water co-catalyst with Au/BN in RT CO oxidation Au/BN catalyst shows a quick increasing CO oxidation with increase of moisture concentration upto 100% relative humidity (RH) How water can enhance RT CO oxidation over Au/BN is found related to intermediate species of hydroperoxyl (*OOH) and CO(H2O)2 complex upon O2-H2O and CO-H2O cofeedings, respectively Injection of isotope labeled H218O demonstrates that OH from H2O takes part in the process of CO2 formation and proton transfer to oxygen leading production of CO2 The second focus in this work is the effect of calcination conditions on water adsorption behaviors and catalyst activity in RT CO oxidation over Au/BN Ex situ XPS analysis demonstrates only metallic gold (Au0) dominated on Au/BN1 and Au/BN2 after calcination at temperatures from 300 to 600oC, with the exception of Au/BN1-300 and Au/BN2-600 The existence of Au+ (plus charged gold) on Au/BN1-300 and Au/BN2-600 presents less active CO oxidation in nominal dry and wet conditions Increasing calcination temperature results in increase of both physisorption and chemisorption of water on Au/BN1 and Au/BN2, which can be described by Henry’s model and non-dissociative Langmuir model, respectively This suggests that H2O adsorbs probably at the interface between Au and BN and that COad on Au surface may interact with the adsorbed H2O to form CO-(H2O)n and *OOH species That also regards to the significant enhancement of moistened RT CO oxidation over Au/BN at elevated calcination temperature Experimental evidences in this section indicates the interfacial perimeter of Au/BN is involved in the activation of CO and O2 The third achievement of this work examines the nature of active site on Au/BN catalyst We examined how an additional H2 treatment at 300oC influence Au/BN1-600, i Au/BN2-450 and Au/BN2-600 Only Au0 governed on Au/BN1 and Au/BN2 as proven by in situ DRIFTS of dry CO adsorption Only a slight increase in nominal dry CO oxidation activity was found over Au/BN after the additional H2 treatment The catalytic activity of wet RT CO oxidation is almost the same over Au/BN1-600 with/without the additional H2 treatment However, a noticeable increase in wet CO oxidation rate over Au/BN2-600 was found after H2 treatment This suggests that Au0 is more likely the active phase than Au+ in water co-feed RT CO oxidation over Au/BN Another contribution of this work is to propose a possible mechanism that is consistent with the spectroscopic data and the kinetic data The kinetic study was performed by varying space velocity and concentration of CO, O2 and H2O and then the kinetic data was reported The reaction order on CO, O2 and H2O was found as 0.5 - 0.9, 0.5 – 0.5, and 0.6 – 1.5, respectively, which are not much influenced by catalyst pretreatment and type of BN (exception of H2O reaction order of 0.3 and 1.04 for Au/BN2-600 and Au/BN2-600-H2, respectively) A mechanism with good species balance is proposed which may explain how water acts as a co-catalyst in RT CO oxidation over Au/BN Au0 is the surface site for COad and O2ad while the interface of Au-BN involved the sites for molecular H2Oad CO(H2O)n complex is formed from the interaction between COad and H2Oad and the rate-determining step is the reaction between CO(H2O)n and O2ad ii Acknowledgements Firstly I would like to express my sincere gratitude to my Ph.D supervisor, Prof Shawn D Lin, for giving me the opportunity to take Ph D study; especially for his advices, guidance, invaluable supports, and infinite patience he has shown me I am also grateful to the members of the Oral Defense Committee for their reading and giving valuable comments I also would like to thank Prof Jyh-Chiang Jiang at NTUST for important discussion of DRIFTS and DFT calculations; Prof Soofin Cheng at National Taiwan University for Propylene Epoxidation preliminary tests; Prof Ching-Shiun Chen at Chang Gung University for some DRIFTS tests; Prof Toyoko Imae for helping me in water adsorption desorption isotherms testing; Staffs in Chemical Engineering Department for their assistances; Ms Wu at the Materials Department, NTUST for assistance with TEM measurements; Ms Ping Hsu at Chemical Engineer Department, NTU for XPS analysis and important discussions I will never forget the laughs, good times, and sweet memories with my lab-mates at E2-301: Yonas Beyene, Hsin-Ying Yang, Cheng-Hong Yu, Guo-Yan Huang, Yi-Ning Chao, Guan-Wei Huang, Yen-Fan Lo, Li-Jia Chen, Szu-Hua Chen, Li-Chun Lin, Yi-Jhen Peng, TzJie Ju, Steven, Van-Huy Nguyen, and with Vietnamese students at NTUST: Ngoc-Quynh-Hoa Le, Đuc- Thang Vo, Minh-Kha Nguyen, Anh- Nguyen Phan, Ngan-Tuyen Nguyen, ThanhTham Tran, Ngoc-Hanh Cao-Luu, et al I would like to sincerely thank Prof Ngoc-Hanh Nguyen, Ho Chi Minh City University of Technology (HCMUT) for abroad enthusiastic supports, unlimited encouragements and fruitful discussions iii I would also truly like to thank my colleagues: Dr Van-Dung Nguyen, HCMUT and Ph.D student Bao-Trung Đang, University of Toulouse, MSc Hoa- Hung Lam, HCMUT for their friendly supports, encouragements and good memories Without unlimited sacrifice of my husband, Van-Tuan Lu, I would have not accomplished this work Be thankful for his parenting our children, Minh-Khoi Lu and KhanhLinh Lu-Tran, throughout four years A great thank to my parents in law for their love and care of us! With honor I would like to present this work to my parents, Van-Khoe Tran and ThuyTien Đo-Thi, who have always loved us and my children unconditionally I will not forget their lessons of energy, patience and determination Last, but not least, I also would like to thank my brother, Thanh-Nghi Tran, and my sister, Lan-Phuong Tran-Thuy, for their constant supports and loves TRAN THUY, TUYET MAI iv Table of Contents Abstract i Acknowledgements iii Table of Contents v List of Abbreviations viii List of Tables xiv List of Schemes xv Literature Review 1 Gold catalysts for CO oxidation 1 1 The important role of Au valence state in CO oxidation 1 Water enhance co oxidation at low temperature over au/metal oxide catalysts 1 Mechanism of CO oxidation over gold catalysts Carbon monoxide (CO) - the silent killer 12 Impact to human 12 2 Impact to climate modification 13 Boron Nitride (BN) 13 Motivation and goal 15 Experimental Section 16 Catalyst preparation 16 1 Methods for preparation of gold catalysts 16 2.1.1.1 Incipient wetness (wet impregnation – IMP) method80 16 2.1.1.2 Deposition – precipitation (DP) method 16 2 Deposition method for synthesis of 1wt% Au/BN 17 2 Characterization 18 2 ICP-AES measurement 18 2 X-ray powder diffraction (XRD) 18 v 2 Scanning Electron Microscope (SEM) 18 2 High Resolution Transmission Electron Microscopy (HRTEM) Analysis 18 2 Adsorption-desorption isotherms 19 2 XPS analysis 19 CO oxidation tests 19 In-situ DRIFTS 21 In situ UV-Vis-DRS 22 Spectroscopic Studies of How Moisture Enhances CO Oxidation over Au/BN at Ambient Temperature 23 Motivation 23 Results 24 Effect of H2O on CO oxidation over Au/BN 24 2 In situ DRIFTS 26 3 In situ UV-Vis-DRS 31 3 Discussion 34 Summary 37 Effect of Calcination Temperature on Water Adsorption Behavior and Au/BN Catalytic Activity in Moistened RT CO Oxidation 38 Motivation 38 Results 39 Effect of PH2O on moistened CO oxidation on Au/BN with various calcination 39 2 In situ DRIFTS of CO and CO-H2O feeding on Au/BN with various calcination 41 Effect of calcination temperature on water adsorption behaviors 42 4 Catalyst Characterization 44 XPS analysis 47 Discussion 53 4 Summary 56 vi Kinetic and Mechanism Study of H2O co-catalyst with Au/BN in Room Temperature CO Oxidation 57 Motivation 57 Results 58 Effect of H2 treatment on dry and wet CO oxidations 58 2 Evidences from in situ DRIFTS 59 Proposed mechanism of H2O co-catalyst with Au/BN in RT CO oxidation 62 Model 1: CO, O2, H2O adsorbed on the same site of Au 62 Model 2: H2Oad on interfacial perimeter () and CO, O2 adsorbed on the same site of Au (*): 64 Discussion 66 Summary 69 Concluding Remarks 71 Recommendations for Future Research 73 References 74 Appendix A 85 Appendix B 90 Appendix C 96 Curriculum Vitae of Author 101 Conferences……………………………………………………………………………… 103 Publications……………………………………………………………………………… 103 vii (a) d =3.4 ± 0.5 30 20 Au/BN1 - 2M - 600 40 d = 3.7 ± 0.8 35 30 25 20 15 10 10 Au/BN2-2M-300 40 Number of particles Number of particles 40 (c) (b) 45 Au/BN1-2M-450 Number of particles 50 50 50 30 d = 3.4 ± 0.5 20 10 0 0 10 11 d = 3.2 ± 0.5 20 10 10 10 11 Au/BN2-2M-600 d = 3.9 ± 0.7 20 10 0 11 30 0 (f) 30 10 40 Number of particles 30 Particle size (nm) Au/BN2-2M-450 d = 2.5 ± 0.2 40 Number of particles Number of particles Au/BN2-2M-400 (e) (d) 50 50 50 20 11 Particle size (nm) Particle size (nm) 40 10 10 11 Particle size (nm) 10 11 Particle size (nm) Particle size (nm) Figure B Gold particle size distribution calculated from TEM images at 145k of magnification of Au/BN1-450 (a); Au/BN1-600 (b) and Au/BN2-300 (c); Au/BN2-450 (d); Au/BN2-400 (e); Au/BN2-600 (f) 0.15 Au/BN1-450 Au/BN1-600 0.15 (a) Au/BN2-2M-600 0.4 0.4 0.3 0.3 Y = 0.0488X + 0.0013 0.05 0.05 R = 0.99  PH2O/NH2O R = 0.99  P/n PH2O/NH2O Y = 0.14X + 0.0072 0.2 y = 0.053x + 0.0067 R = 1.0 (d) 0.2 0.4 0.6 0.8 PH2O (kPa) 1.0 0.00 0.0 0.2 0.4 PH2O (kPa) 0.6 0.8 1.0 0.0 0.0 0.2 0.1 0.1 0.00 0.0 0.5 (c) Au/BN1-2M-450 Au/BN1-2M-600 (b) 0.10 0.10 P/NH2O 0.5 Au/BN2-2M-600 0.2 0.4 0.6 0.8 P 1.0 1.2 1.4 0.0 0.0 0.5 1.0  PH2O (kPa) Figure B Fitting results of nondissociative (a & b) and dissociative (c & d) adsorption Langmuir equations 91 (a) (b) Au/BN1-600 o 600 C 3694 0.09 Absorbance 3750 Absorbance 0.09 Au/BN1-450 0.06 Au/BN1-300 0.03 75 -3 68 o 450 C 0.06 o 300 C 0.03 Au/BN2 h-BN2 0.00 3900 h-BN1 3600 3300 -1 Wavenumber (cm ) 3000 0.00 3900 3600 3300 -1 3000 Wavenumber (cm ) Figure B In situ DRIFTS of CO feeding at 100%RH on h-BN1 and Au/BN1 (a) and on hBN2 and Au/BN2 (b) at 25oC 92 out, B-N Absorbance Absorbance as, B-O in, B-N 1800 1600 1400 -1 Wavenumber (cm ) h-BN2 3500 3000 h-BN1 2500 2000 1500 1000 -1 Wavenumber (cm ) Figure B In situ DRIFTS spectra at various calcination temperatures of h-BN1 and Au/BN1 (a) and of h-BN2 and Au/BN2 (b) (a) (d) 93 (b) (c) (e) (f) Figure B SEM images at 30,000 of magnification of (a) Au/BN1-450; (b) Au/BN1-600 and (c) h-BN2-550, (d) Au/BN2-300; (e) Au/BN2-450; (f) Au/BN2-600 94 80 20 0.0 0.2 0.4 Sample P/Po 0.6 0.8 1.0 Ads Desorption Au/BN1-600 Au/BN1-450 Au/BN1-300 h-BN1 0.2 60 10 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 P/Po 0.0 40 10 Va(cm (STP)/g) Va(cm (STP)/g) 60 15 Va(cm (STP)/g) 15 Va(cm (STP)/g) 80 40 Sample 20 0.4 P/Po 0.6 0.8 1.0 Ads Desorption Au/BN2-600 Au/BN2-450 Au/BN2-300 h-BN2 0.0 0.2 0.4 0.6 0.8 1.0 P/Po Figure B N2 Adsorption-Desorption isotherms of (a) h-BN1 and Au/BN1; (b) h-BN2 and Au/BN2 at various calcination temperature 95 Appendix C 300 4.5 450 4.0 Ln (Rate) Cond Au/BN1 Au/BN2 5.0 3.5 3.0 (a) - 450-H2 Cond Au/BN1 Au/BN2 300 450 600 - Ln (Rate) 5.5 600-H2 2.5 600 450-H2 (b) - 600-H2 2.0 1.5 1.0 0.5 0.0 -1.5 -1.0 -0.5 0.0 0.5 1.5 1.0 2.0 2.5 3.0 3.5 4.0 4.5 Ln (PO2) LN(PCO) 2.0 (c) Lg(Rate) 1.5 1.0 Cond Au/BN1 Au/BN2 450 - 600 - 450-H2 - 600-H2 0.5 2.6 2.8 3.0 3.2 3.4 3.6 -1 10 /T (K ) Figure C Effect of PCO (a) and PO2 (b) on CO oxidation rate at 70 -80%RH over Au/BN; (c) Arrhenius plot of moistened CO oxidation over Au/BN 96 3750 - 3680 Absorbance 3.17 kPa 3698 1.68 kPa 1.2 kPa 3750 3220 CO @ PH2O = Sole H2O@ 3.17 kPa 3900 3600 3300 -1 3000 Wavenumber (cm ) Figure C In situ DRIFTS of CO feeding at 25oC at various PH2O on Au/BN1-600-H2 (solid line) and Au/BN2-450-H2 (dash line), in the range of 3900 – 2800 cm-1 97 2.0 Absorbance Absorbance 2.0 600-H2 1.5 450-H2 0.5 B-N 2.5 2.5 1.0 B-N 3.0 B-N B-N 3.0 1.5 600-H2 1.0 300-H2 Au/BN1 0.5 450-H2 300-H2 Au/BN2 h-BN1 0.0 0.0 3500 3000 2500 2000 1500 1000 3500 3000 2500 2000 1500 1000 -1 -1 Wavenumber (cm ) 1.0 Au/BN2- 600-H2 450-H2 1.0 (1615 - 1383) Absorbance Absorbance Wavenumber (cm ) Au/BN1-600-H2 450-H2 h-BN2 300-H2 0.5 (1615 - 1387) 300-H2 0.5 h-BN1-550-H2 h-BN2-550-H2 0.0 1800 1700 1600 1500 1400 1300 0.0 1800 -1 Wavenumber (cm ) 1600 1500 1400 1300 -1 Wavenumber (cm ) 0.10 1.8 1.6 3750 0.08 1.4 Absorbance 1.2 Absorbance 1700 1.0 0.8 0.06 0.04 0.6 0.4 h-BN1-550-H2-300 h-BN2-550-H2-300 0.02 0.2 0.0 3500 3000 2500 2000 1500 1000 -1 Wavenumber (cm ) 0.00 3900 3600 3300 -1 3000 Wavenumber (cm ) 98 Figure C In situ DRIFTS spectra of treatments of Au/BN1 and Au/BN2 in H2; KBr as reference sample 0.14 0.12 Au/BN1-450-H2-300 H2O+CO+O2 0.12 H2O+O2 0.10 Absorbance Absorbance 0.10 2113 0.08 CO+O2+H2O 0.06 CO+H2O 0.04 0.06 0.04 CO/N2 0.02 0.08 AuBN1-450-H2 2135 H2O+CO CO+O2 0.02 CO/AuBN1-450 0.00 2400 2300 2200 2100 -1 0.00 3900 2000 3600 Wavenumber (cm ) 0.14 Au/BN1-450-H2-300 3300 -1 3000 Wavenumber (cm ) Au/BN1-450-H2-300 H2O+CO+O2 0.12 H2O+CO+O2 0.08 H2O+O2 0.06 0.04 Absorbance Absorbance 0.10 0.02 H2O+O2 H2O+CO CO+O2 0.02 H2O+CO CO+O2 0.00 0.00 1800 1500 -1 Wavenumber (cm ) 1200 1100 1000 900 -1 800 Wavenumber (cm ) Figure C In situ DRIFTS of CO, H2O and CO-H2O; O2-H2O feedings over Au/BN2-450H2 at 25oC 99 0.020 H2O+CO Purge dry O2: 0.015 min 0.02 Absorbance Absorbance Purge dry CO: 0.010 0.01 0.005 Au(O)2 O-OH 849 H2O + O2 Growth of OO-H 0.000 1200 1100 1000 900 Diminution of OOH 0.00 800 1200 -1 Wavenumber (cm ) 0.025 Au/BN1-450-H2-300 900 -1 800 0.010 min 0.010 O-OH Purge dry O2: Absorbance Absorbance 1000 H2O+CO 0.020 0.015 1100 Wavenumber (cm ) 0.008 0.006 Purge dry O2 H2O + CO 0.005 0.000 2400 0.004 2300 2200 2100 2000 1250 1150 1100 1050 Wavenumber (cm ) H2O+CO Purge dry O 0.06 Absorbance 1200 -1 -1 Wavenumber (cm ) min 0.03 0.00 3900 Au/BN1-450-H2-300 3600 3300 -1 Wavenumber (cm ) 3000 Figure C In situ DRIFTS show consumption of *OOH intermediate and CO(H2O)n complex under dry CO and dry O2, respectively 100 Curriculum Vitae of Author Personal Information Full Name: TRAN THUY TUYET MAI Birth Day: Dong Thap Province, Vietnam Nationality: Vietnamese Current address: National Taiwan University of Science and Technology (NTUST) No 43, Keelung Rd., Sec 4, Taipei City 106, Taiwan Email: tuyetmai@hcmut.edu.vn Educational Background 2013/9 – 8/2017: Doctor of Philosophy (PhD.), National Taiwan University of Science and Technology (NTUST), Department of Chemical Engineering, Taiwan Supervisor: Professor Shawn D Lin 2002 – 2005: Master of Science (M.Sc.), Ho Chi Minh City University of Technology, Chemical Engineering Department, Division of Physico-Chemical Engineering, Vietnam Supervisor: Professor Ngoc-Hanh Nguyen 1997- 2002: Bachelor of Engineering, Ho Chi Minh City University of Technology, Chemical Engineering Department, Division of Physico-Chemical Engineering, Vietnam Supervisor: Professor Ngoc-Hanh Nguyen 101 Professional experiences and Honors 2007/5 – now: Lecturer, Ho Chi Minh City University of Technology (HCMUT), Chemical Engineering Department , Physico Chemical Engineering Division, Vietnam 2006 – 2007: R & D Lab, A My Gia Com., Ltd, HCM city, Vietnam 2005 – 2006: Nano Technology Lab, SaiGon Hi-Tech Park, R&D Center Vietnam 2002 – 2004: Science and Technology Department, Plastic and Rubber Technology Center, HCM city, Vietnam 2003: The 3rd prize in “EUREKA AWARD 2003”, HCM City’s Communist Youth Union, Vietnam 2002: The 2nd prize in “SCIENCE STUDIES for STUDENTS”, the Minister of Ministry of Education and Training, Vietnam 2002: The 2nd prize in “TECHNOLOGICAL CREATIONS VIFOTEC” in, VIFOTEC Sponsorship Council, Vietnam 102 Conferences [1] Tuyet-Mai Tran-Thuy, Chin-Chih Chen, and Shawn D Lin, In Situ Spectroscopy Studies of How Moisture Promotes Ambient CO Oxidation over Au/BN, The 35th Taiwan Symposium on Catalysis and Reaction Engineering & The Ministry of Science and Technology Project Research Achievements Conference, 22 - 23 /June/ 2017, I-Shou University, Kaohsiung City, Taiwan (Oral Presentation) [2] Tuyet-Mai Tran-Thuy, Chin-Chih Chen, and Shawn D Lin, Enhanced CO oxidation on Au/BN through elevation of relative humidity, The 16th International Congress on Catalysis, Beijing, China, July 3-8, 2016 (Poster Presentation) [3] Thuy Tuyet-Mai Tran, Shawn D Lin, and Ngoc Hanh Nguyen, presentation “Gas Phase Oxidation of Benzyl Alcohol on M-OMS-2”, 2015 International Conference on Nanospace Materials, 23-25 June 2015, National Taiwan University, Taiwan, 2015 (Poster Presentation) 103 Publications [1] Tuyet-Mai Tran-Thuy and Shawn D Lin, Kinetic analysis and proposed mechanism of moisture enhanced CO oxidation over Au/BN at ambient temperature, Article in Preparation [2] Tuyet-Mai Tran-Thuy and Shawn D Lin, Effect of Calcination Conditions on Water Adsorption Behavior and Catalyst Activity of Au/BN in Moisture Enhanced CO Oxidation at Room Temperature, Article in Preparation [3] Tuyet-Mai Tran-Thuy, Chin-Chih Chen, and Shawn D Lin, Spectroscopic Studies of How Moisture Enhances CO Oxidation over Au/BN at Ambient Temperature, ACS Catal 2017, 7, 4304−4312 Publications in Vietnamese Journals & Proceedings: [1] Tran Thuy Tuyet Mai, Vu Van Hai, Nguyen Ngoc Hanh, M-OMS-2: Synthesis by Sogel rout and catalyst for green oxidation of benzyl alcohol, ISCE2013, 267 - 272 [2] Tran Thuy Tuyet Mai, Nguyen Minh Hau, Luong Anh Quoc, Nguyen Ngoc Hanh, Nano CuO/SBA-16: synthesis from mesosilica and n-[3-(trimethoxysilyl)propyl] ethylene diamine, Journal of Science and Technology, 50, 3D, (2012), 974 - 980 [3] Tran Thuy Tuyet Mai, Nguyen Huy Hung, Nguyen Ngoc Hanh, OMS-2/bentonite pellets: preparation and catalytic in total oxidation of toluene, Journal of Chemistry, 50, 50A, (2012), 305 - 309 [4] Tran Thuy Tuyet Mai, Nguyen Minh Hau, Luong Anh Quoc, Nguyen Ngoc Hanh, Synthesis of CuO/SBA-16 material from mesosilica modified by amino, Journal of Chemistry, 49, 2ABC, (2011), p 898-902 [5] Le Tuyet Mai Ha, Tran Thuy Tuyet Mai, Nguyen Ngoc Hanh, Synthesis of OMS-2 supported on mesoporous silica SBA-16, Journal of Science and Technology, 48, 2A (2010), p.937-945 [6] Vo Dinh Truc, Tran Thuy Tuyet Mai, Nguyen Ngoc Hanh, Catalytic oxidation of toluen with molecular oxygen over OMS-2 material, Proceedings of The 2004 International Symposium on Advanced Science and Engineering, May 2004 (Vietnam), p.497 – 501 104 [7] Nguyen Thanh Truc, Tran Thuy Tuyet Mai, Nguyen Ngoc Hanh, Synthesis of octahedral molecular sieves OMS-1, Proceedings of the 8th Conference Science and Technology, April (2002), HCM city, Vietnam, p.69 – 75 105 ... dependency on moisture concentration Moisture plays as a promoter at low concentration but as an inhibitor at high concentration In the absence of O2, no CO2 could be detected under CO- H2O cofeeding over. .. room -temperature conditions of CO oxidation This indicates that H2O can influence CO oxidation over Au catalysts but is not a reactant for the formation of CO2 Bond and Thompson9 proposed that CO. .. Dependence of water in CO oxidation over Au/TiO2 (293 K, 1% CO, 20% O2, SV = 36 L/g catalyst/min).43 (b) Moisture order of CO oxidation over Au/TiO2 derived from Figure 1.5a 1 Mechanism of CO oxidation