Catalytic activity and reaction mechanism of Au/TiO 2 for the reduction of NO x by propene TOKYO INSTITUTE OF TECHNOLOGY DEPARTMENT OF INTERNATIONAL DEVELOPMENT ENGINEERING Nguyen Quang Long Dissertation submitted in partial fulfillment of requirements for a doctoral degree of engineering Catalytic activity and reaction mechanism of Au/TiO 2 for the reduction of NO x by propene By Nguyen Quang Long 06D51501 (Supervised by Professor Hirofumi Hinode) DEPARTMENT OF INTERNATIONAL DEVELOPMENT ENGINEERING GRADUATE SCHOOL OF SCIENCE AND ENGINEERING TOKYO INSTITUTE OF TECHNOLOGY 2009 i Table of Content CHAPTER 1 INTRODUCTION 1 1.1. Outline 1 1.2. Background 1 1.2.1. Automobile exhaust 1 1.2.2. Emission limitations 2 1.2.3. Lean-burn engine and effectiveness of three way catalysts 4 1.3. Treatment of NO x from lean-burn exhaust 5 1.3.1. NO x storage reduction 5 1.3.2. Selective catalytic reduction of NO x 6 1.4. Gold as a catalyst 7 1.4.1. A brief history of gold catalysis 7 1.4.2. Potential uses of gold as a catalyst 9 1.5. Objectives of the research and the structure of this thesis 10 References 12 CHAPTER 2 REVIEW OF RELATED LITERATURE 13 2.1. Outline 13 2.2. Reduction of NO x by hydrocarbons 13 2.2.1. Zeolite-based as catalysts 13 2.2.2. Non-zeolitic catalysts 15 2.3. Mechanisms of the reduction of NO x by hydrocarbons 22 2.3.1. Adsorption-Dissociation mechanism 22 2.3.2. Oxidation-reduction mechanism 24 2.4. Gold catalysts for NO x reduction by hydrocarbons 25 References 28 CHAPTER 3 CATALYTIC ACTIVITY OF Au/TiO 2 30 3.1. Outline 30 3.2. Experimental 30 3.2.1. Preparation and characterization of the catalysts 30 ii 3.2.2. Measurement of the catalytic activity 31 3.3. Results and discussion 32 3.3.1. Influence of preparation conditions 32 3.3.2. Influence of TiO 2 crystalline type on NO x reduction 36 3.3.3. Influence of gold loading levels 38 3.3.4. Influence of the feed concentrations 40 3.4. Conclusions 43 References 44 CHAPTER 4 EFFECT OF CeO 2 , Mn 2 O 3 ON THE CATALYTIC ACTIVITY OF Au/TiO 2 45 4.1. Outline 45 4.2. Experimental 45 4.2.1. Preparation and characterization of the catalysts 45 4.2.2. Measurements of the catalytic activity 46 4.2.3. Temperature program desorption experiments 46 4.3. Results and discussion 47 4.3.1. Effect of CeO 2 addition 47 4.3.2. Effect of Mn 2 O 3 addition 49 4.3.3. Catalytic activity for NO oxidation to NO 2 50 4.3.4. Catalyst characteristics and NO x desorbed in TPD measurement 51 4.4. Conclusion 53 References 54 CHAPTER 5 REACTION MECHANISM OVER Au/TiO 2 55 5.1. Outline 55 5.2. Experimental 55 5.3. Results 57 5.3.1. Formation of adsobed species during co-adsorption of reactants 57 5.3.2. Formation of adsorbed species during SCR reaction 63 5.3.3. Consumption of adsorbed species 69 5.4. Discussion of reaction mechanism 73 iii 5.5. Conclusions 75 References 76 CHAPTER 6 MECHANISTIC STUDY ON THE EFFECT OF CeO 2 AND Mn 2 O 3 77 6.1. Outline 77 6.2. DRIFTS results and discussion on CeO 2 -added Au/TiO 2 catalyst 77 6.2.1. Co-adsorption of reactants on CeO 2 77 6.2.2. Effect of CeO 2 on the formation of adsorbed species 80 6.2.3. Effect of CeO 2 on the consumption of adsorbed species 86 6.2.4. Conclusions of the influence of CeO 2 on the reaction mechanism 88 6.3. DRIFTS results and discussion on Mn 2 O 3 -added Au/TiO 2 catalyst 89 6.3.1. Co-adsorption of reactants on Mn 2 O 3 89 6.3.2. Effect of Mn 2 O 3 on the formation of adsorbed species 91 6.3.3. Effect of Mn 2 O 3 on the consumption of adsorbed species 95 6.3.4. Conclusions of the influence of Mn 2 O 3 on the reaction mechanism 97 6.4. Summary of the effect of CeO 2 and Mn 2 O 3 98 References 98 CHAPTER 7 GENERAL CONCLUSIONS 99 ACKNOWLEDGEMENTS 101 LIST OF ORIGINAL PUBLICATIONS 102 iv List of Figures Figure 1-1 The emissions regulation for heavy-duty diesel vehicle [7] 3 Figure 1-2 Fuel consumption and 3-way performance of a gasoline engine as a function of air-fuel (A/F) ratio [10] 5 Figure 1-3 Possible mechanism of the NO x storage-reduction on NSR catalyst [10] 6 Figure 1-4 The numbers of published articles concerning gold catalysts in recent years (Data from ISI) 8 Figure 2-1 Effect of H 2 O on NO conversion to N 2 and N 2 O on Pt/Na–ZSM-5 [7] 14 Figure 2-2 NO conversion and selectivity for Ga 2 O 3 /Al 2 O 3 and Ga-ZSM-5 in the absence or presence of H 2 O [14]. 16 Figure 2-3 Effects of the hydrothermal treatment on the activity of Cu-Al 2 O 3 and Cu- ZSM-5 [15]. 16 Figure 2-4 Activities of different noble metal catalysts for the selective reduction of NO x [19] 18 Figure 2-5 Classification of the cooperation effect of catalytic species. (a) Multiple-stage catalysts, (b) mechanical or physical mixture catalysts, and (c) multifunctional catalyst [21] 19 Figure 2-6 NO reduction conversion as a function of temperature mixtures of Ni–Ga oxide with different amounts of Mn 2 O 3 . [27]. 20 Figure 2-7 Conversion of NO to N 2 over Au/Al 2 O 3 , CeO 2 , mechanical mixture, and dual bed Au/Al 2 O 3 -CeO 2 or CeO 2 -Au/Al 2 O 3 [29] 21 Figure 2-8 Proposed mechanism for C 3 H 6 -SCR over Pt-containing catalysts [39] 23 Figure 2-9 Proposed mechanism of C 3 H 6 -SCR over Cu/Al 2 O 3 [43] 24 Figure 2-10 Temperature dependence of NO conversion to N 2 over Al 2 O 3 and gold supported on a variety of metal oxides [47] 26 Figure 3-1 Schematic diagram of the catalytic activity test set-up 32 Figure 3-2 XRD patterns of rutile support Ti6 and Au(1wt.%)/Ti6 with various mass ratios PVA/Au 33 Figure 3-3 XRD patterns of Au/TiO 2 with different TiO 2 types and Au loading levels. 34 v Figure 3-4 TEM images of Au/TiO 2 : Au(1wt.%)/Ti4 (a), Au(1wt.%)/Ti6 (b), Au(1wt.%)/Ti7 (c) 35 Figure 3-5 Size distribution of Au particles on different titania supports 35 Figure 3-6 The effect of titania type on the HC-SCR activity of Au/TiO 2 37 Figure 3-7 The effect of Au content on the HC-SCR activity as a function of temperature. 38 Figure 3-8 The effect of concentration of NO x and C 3 H 6 on the activity of Au(0.1wt.%)/Ti7 41 Figure 3-9 The effect of H 2 O on the NO x reduction activity of Au/TiO 2 catalysts: without H 2 O or with 5% H 2 O 42 Figure 3-10 The stability of 0.1%Au/Ti7 catalysts after dry-test and wet-test 43 Figure 4-1 Catalytic performance of the mechanical mixtures of Au/TiO 2 and CeO 2 : (a) NO conversion to N 2 and (b) C 3 H 6 conversion to CO 2 48 Figure 4-2 Catalytic performance of the mechanical mixtures of Au/TiO 2 and Mn 2 O 3 : (a) NO conversion to N 2 and (b) C 3 H 6 conversion to CO 2 49 Figure 4-3 Activity of the catalysts for the oxidation of NO to NO 2 50 Figure 4-4 XRD patterns of singles and mixtures of 1%Au/TiO2 and MOx (M=Ce, Mn). 51 Figure 4-5 The TPD profiles of the NO x desorption from NO and O 2 pre-adsorbed samples 52 Figure 5-1 Schematic diagram of the DRIFTS measurement 55 Figure 5-2 Experimental procedure of DRIFTS measurement 56 Figure 5-3 DRIFTS spectra of adsorbed species over Au/TiO 2 after exposing in different gas flows for 40 min at 150 o C 57 Figure 5-4 DRIFTS spectra of adsorbed species over Au/TiO 2 after exposing in flow of NO/O 2 /He for 40 min at different temperatures 59 Figure 5-5 Comparison spectra of surface adsorbed species between Au/TiO 2 and TiO 2 after exposing to NO/O 2 /He for 40 min at 200 o C and 300 o C. 60 Figure 5-6 DRIFTS spectra of adsorbed species over Au/TiO 2 after exposing in flow of C 3 H 6 /O 2 /He for 40 min at different temperatures 61 vi Figure 5-7 DRIFTS spectra of adsorbed species over TiO 2 (a) and Au/TiO 2 (b) after exposing in C 3 H 6 /O 2 /He and Au/TiO 2 after exposing inC 3 H 6 /He (c) for 40 min at 200 o C 63 Figure 5-8 DRIFTS spectra of adsorbed species after 40 min in SCR reaction at different temperatures 64 Figure 5-9 DRIFTS spectra of adsorbed species after 40 min in reaction condition over TiO 2 and Au/TiO 2 . 66 Figure 5-10 DRIFTS spectra of adsorbed species during the SCR reaction at 200 o C as a function of time 67 Figure 5-11 DRIFTS spectra of adsorbed species during the SCR reaction at 300 o C over TiO 2 , 0.1%Au/TiO 2 , and 1%Au/TiO 2 for 5’ (a), 20’ (b), and 40’ (c) 68 Figure 5-12 DRIFTS spectra recorded over Au/TiO 2 after flowing of C 3 H 6 /O 2 /He for 40 min followed by purging He for 20 min (a), then flowing of NO/O 2 /He. 69 Figure 5-13 DRIFTS spectra recorded over Au/TiO 2 after flowing of C 3 H 6 /O 2 /He for 40 min followed by purging He for 20 min (a), then flowing of NO/O 2 /He. 70 Figure 5-14 DRIFTS spectra recorded over Au/TiO 2 at 300 o C after flowing of C 3 H 6 /O 2 /He for 40 min followed by purging He for 20 min then flowing of He (a), O 2 /He (b), and NO 2 /He (c) 71 Figure 5-15 DRIFTS spectra recorded over Au/TiO 2 after flowing of NO/O 2 /He for 40’ followed by purging He for 20’, then flowing of C 3 H 6 /O 2 /He. 72 Figure 5-16 Schematic diagram of reaction mechanism over Au/TiO 2 catalyst 75 Figure 6-1 DRIFTS spectra of adsorbed species over CeO 2 after exposing in NO/O 2 (a) and C 3 H 6 /O 2 (b) for 40 min at various temperatures. 78 Figure 6-2 DRIFTS spectra of adsorbed species over Au/Ti-Ce after exposing in NO/O 2 (a) and C 3 H 6 /O 2 (b) for 40 min at various temperatures 80 Figure 6-3 Comparison of DRIFTS spectra of adsorbed species over different samples after exposing in NO/O 2 (a) and C 3 H 6 /O 2 (b) for 40 min at 200 0 C 80 Figure 6-4 DRIFTS spectra of adsorbed species over Au-Ti-Ce after exposure to reaction condition NO/C 3 H 6 /O 2 for 40 mins at various temperatures (a) and at 200 o C in various reaction times (b) 82 vii Figure 6-5 Comparison of DRIFTS spectra of adsorbed species over different samples after exposure to reaction condition NO/C 3 H 6 /O 2 for 40 mins at 200 0 C 83 Figure 6-6 Comparison of (-NCO) peak’s area on Au/TiO 2 and Au/Ti-Ce at 250 o C as a function of reaction time. Reaction condition: NO: 1500 ppm, C 3 H 6 : 1500ppm, O 2 : 10% in He. 84 Figure 6-7 Change of (-NCO) peak’s area on Au/TiO 2 under streams of NO+O 2 or NO 2 . The sample was pre-exposed to the reaction mixture NO/C 3 H 6 /O 2 for 40 minutes followed by purging He for 20 minutes 85 Figure 6-8 DRIFTS spectra in (C-H) stretching region of adsorbed species over (a) Au/TiO 2 , (b) CeO 2 and (c)Au/Ti-Ce after exposing in C 3 H 6 /O 2 for 40 mins followed by purging He for 20 min, and then under flowing of NO/O 2 for 5 mins or 40 mins at 250 o C 87 Figure 6-9 DRIFTS spectra of adsorbed species over (a) Au/TiO 2 , (b) CeO 2 and (c)Au/Ti-Ce after exposing in NO/O 2 for 40 mins followed by purging He for 20 min, and then under flowing of C 3 H 6 /O 2 for 5 mins or 40 mins at 250 o C 88 Figure 6-10 DRIFTS spectra of adsorbed species over Mn 2 O 3 after exposing in NO/O 2 (a) and C 3 H 6 /O 2 (b) for 40 min at various temperatures 90 Figure 6-11 DRIFTS spectra of adsorbed species over Au/Ti-Mn after exposing in NO/O 2 (a) and C 3 H 6 /O 2 (b) for 40 min at various temperatures 91 Figure 6-12 Comparison of DRIFTS spectra of adsorbed species over different samples after exposing in (a) NO/O 2 and (b) C 3 H 6 /O 2 for 40 min at 200 0 C 92 Figure 6-13 DRIFTS spectra of adsorbed species over Au-Ti-Mn after exposure to reaction condition NO/C 3 H 6 /O 2 for 40 mins at various temperatures (a) and at 200 0 C for various reaction times (b) 93 Figure 6-14 Comparison of DRIFTS spectra of adsorbed species over over different samples after exposure to reaction condition NO/C 3 H 6 /O 2 for 40 mins at 200 0 C 94 Figure 6-15 DRIFTS spectra of adsorbed species over (a) Au/TiO 2 , (b) Mn 2 O 3 and (c)Au/Ti-Mn after exposing in C 3 H 6 /O 2 for 40 mins followed by purging He for 20 min, and then under flowing of NO/O 2 for 5 mins or 40 mins at 200 o C. 95 viii Figure 6-16 DRIFTS spectra of adsorbed species over (a) Au/TiO 2 , (b) Mn 2 O 3 and (c)Au/Ti-Mn after exposing in NO/O 2 for 40 mins followed by purging He for 20 min, and then under flowing of C 3 H 6 /O 2 for 5 mins or 40 mins at 200 o C 96 [...]... of NOx by hydrocarbons over gold supported on a sulfur-resistant material, TiO2 Specifically, the objectives of the present research are as follows: 1 To prepare and test the catalytic activity of nano-sized Au/TiO2 for SCR of NOx by propene 2 To investigate the effect of mechanical additions of CeO2 and Mn2O3 to Au/TiO2 on the catalytic activity 3 To investigate the reaction mechanism of the SCR by. .. for NOx treatment of lean-burn engine exhaust and (2) the real potential of using gold based catalyst for the reduction of NOx by hydrocarbons It is also evidenced that the more studies should be conducted in order to understand the catalytic activity of Au-based catalyst This study, in general, aims to investigate the catalytic activity and the reaction mechanism of Au-based catalysts for the reduction. .. propene over Au/TiO2 4 To understand the mechanistic effect of the additional CeO2 and Mn2O3 This thesis consists of seven chapters, and the summary of each chapter is given as follows: Chapter 1 This chapter provides the background about the necessary of catalyst development for NOx removal from lean-burn exhaust and the potentials of using gold catalysts for the reduction of NOx by hydrocarbons The. .. Additionally, the sulfur poisoning is a serious problem of using Al2O3 support Therefore, further researches should be studied in order to understand the catalytic activity of gold-based catalysts on the SCR of NOx by hydrocarbons 1.5 Objectives of the research and the structure of this thesis Two important conclusions that can be drawn from the above background are (1) the necessary of developing catalysts for. .. SCR of NOx from lean exhaust, Al2O3 supported gold catalysts were attempted in some studies for the reduction of NOx by hydrocarbons [19-22] These studies have almost focused on propene as a reductant The advantages of gold-based catalysts for propene- SCR are their more excellent than PGMs based catalysts in the selectivity for N2 and the tolerance to the presence of water [23] However, the high activity. .. methods for converting NOx to N2 under lean conditions: NOx storage reduction and selective catalytic reduction of NOx 1.3.1 NOx storage reduction The NOx storage reduction method (NSR) was developed by Toyota researchers for the control of NOx emission under lean-burn conditions In this approach, the catalyst functions with alternatively lean and rich conditions Under lean conditions, excess NOx is...List of Tables Table 3-1 The effect of PVA and pH in preparation of Au(1wt.%)/Ti6 by metal sol method 33 Table 3-2 The actual Au loading by ICP and Au particle size of 1%Au/TiO2 by TEM 36 Table 4-1 Catalytic behaviors of the mechanical mixtures of Au/TiO2 and MOx 47 Table 4-2 Specific surface areas and amount of NOx desorbed from the catalysts 52 Table 5-1 Band assignment for adsorbed... species and leave active sites for the following adsorption step This mechanism explains the fact that there is a large amount of N2O generated during NO reduction using Pt-containing catalysts The importance of the reducing agent is rapidly remove O(ads) formed during the dissociations of NO and also O2 to liberate active sites for other NO to be adsorbed and dissociated The mechanism for N2 formation... studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) over Au/TiO2 for SCR by propene is extensively reported The formation and consumption of surface adsorbed species is studied The reaction mechanism is discussed Chapter 6 In this chapter, the explanations for the promotion in catalytic activity after the additions of CeO2 and Mn2O3 to Au/TiO2 are discussed based on the results... to improve the catalytic activity for SCR by propene They found out that mixture of Ce-ZSM-5 and Mn2O3 (and also CeO2) showed higher NO reduction activity than Ce-ZSM-5 Whereas, mechanical mixing with CuO or Cr2O3 decreased the activity of Ce-ZSM-5 The group proposed that Mn2O3 and CeO2 are served as NO oxidation catalysts, while CuO and Cr2O3 accelerate the undesirable oxidation reaction of C3H6 NO . partial fulfillment of requirements for a doctoral degree of engineering Catalytic activity and reaction mechanism of Au/TiO 2 for the reduction of NO x by propene By Nguyen Quang. Catalytic activity and reaction mechanism of Au/TiO 2 for the reduction of NO x by propene TOKYO INSTITUTE OF TECHNOLOGY DEPARTMENT OF INTERNATIONAL DEVELOPMENT. function of temperature. 38 Figure 3-8 The effect of concentration of NO x and C 3 H 6 on the activity of Au(0.1wt.%)/Ti7 41 Figure 3-9 The effect of H 2 O on the NO x reduction activity of