Electrochemical reduction of NOx - DTU Orbit

More documents

Recommendations

Info

Abstract Abstract NO and NO2 (collectively referred to as NOx) are air pollutants, and the largest single contributor to NOx pollution is automotive exhaust. This study investigates electrochemical deNOx, a technology which aims to remove NOx from automotive diesel exhaust by electrochemical reduction of NOx to N2 and O2. The focus in this study is on improving the activity and selectivity of solid oxide electrodes for electrochemical deNOx by addition of NOx storage compounds to the electrodes. Two different composite electrodes, La0.85Sr0.15MnO3-δ-Ce0.9Gd0.1O1.95 (LSM15-CGO10) and La0.85Sr0.15FeO3-δ-Ce0.9Gd0.1O1.95 (LSF15-CGO10), have been investigated in combination with three different NOx storage compounds: BaO, K2O and MnOx. The main focus in the investigation has been on conversion measurements and electrochemical characterization, the latter by means of electrochemical impedance spectroscopy and cyclic voltammetry. In addition, infrared spectroscopy has been performed to study how NOx adsorption on the electrodes is affected by the presence of the aforementioned NOx storage compounds. Furthermore, non-tested and tested electrode microstructures have been thoroughly evaluated by scanning electron microscopy. The studies reveal addition of MnOx or K2O to the electrodes cause severe degradation problems, and addition of these compounds is thus unsuitable for electrode improvement. In contrast, addition of BaO to LSM15-CGO10 electrodes is shown to have a very positive impact on the NOx conversion. The increased NOx conversion, following the BaO addition, is attributed to a combination of 1) a decreased electrode polarisation resistance and 2) an altered NOx adsorption. The NOx conversion is observed to increase strongly with polarisation, and during 9 V polarisation of an 11-layer porous cell stack, 60% NOx conversion in a mixture of 1000 ppm NO and 10% O2 is achieved at 400 °C on entirely ceramic electrodes. This project thus demonstrates electrochemical deNOx is possible without the presence of noble metals at realistic operating conditions. However, several questions remain, among these how the the BaO interacts with the solid oxide electrodes and how the electrochemical cell is optimally operated during electrochemical deNOx. ii
Dansk resumé Dansk resumé NOx er en fællesbetegnelse for gasserne NO og NO2. NOx udledning bidrager til luftforureningen, og det største enkeltbidrag til NOx forureningen stammer fra biludstødning. I dette projekt studeres teknologien elektrokemisk deNOx, som er rettet mod rensning af dieseludstødning ved hjælp af elektrokemisk reduktion af NOx til N2 og O2. Fokus i projektet er på forbedring af fastoxid elektroders aktivitet og selektivitet i forhold til elektrokemisk deNOx, forbedringen forsøges opnået ved tilføjelse af NOx lagrings forbindelser til elektroderne. To forskellige typer komposit elektroder, La0.85Sr0.15MnO3-δ-Ce0.9Gd0.1O1.95 (LSM15-CGO10) og La0.85Sr0.15FeO3-δ-Ce0.9Gd0.1O1.95 (LSF15-CGO10), er blevet undersøgt i kombination med tre forskellige NOx lagrings forbindelser: BaO, K2O og MnOx. Hovedfokus i undersøgelsen har været på omsætningsmålinger og elektrokemisk karakterisering, sidstnævnte ved hjælp elektrokemisk impedans spektroskopi og cyklisk voltammetri. Derudover er der udført infrarød spektroskopi for at undersøge, hvordan NOx adsorptionen på elektroderne påvirkes af tilstedeværelsen af de førnævnte NOx lagrings forbindelser. Endelig er mikrostrukturen af testede og ikke-testede elektroder blevet grundigt undersøgt med scanning elektron mikroskopi. Undersøgelsen viser, at tilføjelse af MnOx og K2O er uegnet til forbedring af elektroderne, da tilstedeværelse af MnOx og K2O medfører en fatal degradering. Derimod har tilføjelse af BaO til elektroderne en klart positiv effekt på NOx omsætningen. Den øgede NOx omsætning som følge af BaO tilsætning kan tilskrives en kombination af 1) en sænkning af elektrodens polariserings- modstand og 2) en ændring i NOx adsorptionen. NOx omsætningen stiger kraftigt med stigende polarisering og ved 9 V polarisering ved 400 °C af en 11-lags, porøs cellestak opnås 60 % NOx omsætning i en blanding bestående af 1000 ppm NO og 10 % O2, denne omsætning opnås på udelukkende keramiske elektroder. Dette projekt demonstrerer dermed, at elektrokemisk deNOx er mulig under realistiske forhold uden brug af ædelmetaller. Flere spørgsmål savner dog stadig et svar, heriblandt hvordan BaO interagerer med fastoxid elektroderne samt hvordan en elektrokemisk celle skal drives optimalt under elektrokemisk deNOx. iii
Page 1 and 2: Department of Energy Conversion and
Page 3: Preface Preface This thesis is subm
Page 7 and 8: Table of Contents 5.3 Experimental
Page 9 and 10: 1 Introduction 1 Introduction NOx i
Page 11 and 12: 1 Introduction 3, 12 Table 1. Emiss
Page 13 and 14: O 1 Introduction 2 2 NOx storage: N
Page 15 and 16: 1 Introduction the electrode materi
Page 17 and 18: 1 Introduction The main focus of th
Page 19 and 20: 2 Materials 2 Materials In this pro
Page 21 and 22: 2 Materials used promoter in conven
Page 23 and 24: 2.4 Material properties 2 Materials
Page 25 and 26: 3 Experimental Figure 1. Symmetric
Page 27 and 28: 3.2 Fabrication of electrodes 3 Exp
Page 29 and 30: 3 Experimental 3) Covering the cell
Page 31 and 32: 3 Experimental NO2* which decays to
Page 33 and 34: 4 DRIFT study of NOx adsorption on
Page 55 and 56:
4.5 Conclusions 4 DRIFT study of NO
Page 57 and 58:
5 Improvement of LSM15-CGO10 electr
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
6 NOx-conversion on Porous LSF15-CG
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
7.1.3 SEM 7 NOx-conversion on LSF15
Page 113 and 114:
7 NOx-conversion on LSF15-CGO10 cel
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
8 NOx-conversion on LSM15-CGO10 cel
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
8.5 Discussion 8 NOx-conversion on
Page 141 and 142:
Page 143 and 144:
8.6 Conclusion 8 NOx-conversion on
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
9.4 Conclusion 9 NOx-conversion on
Page 159 and 160:
10 Measurements on LSM15-CGO10 elec
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
11 Construction of an in situ XANES
Page 181 and 182:
Page 183 and 184:
11.3 Experimental 11.3.1 Design of
Page 185 and 186:
Page 187 and 188:
11.4 Results 11.4.1 Impedance measu
Page 189 and 190:
11.4.2 XANES 11 Construction of an
Page 191 and 192:
Page 193 and 194:
12 Overall Discussion, Conclusion a
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
12.3 Outlook 12 Overall Discussion,
Page 201 and 202:
References References 1 G. Rayner-C
Page 203 and 204:
26 T. Hibino, Chem. Lett., 1994, 5,
Page 205 and 206:
50 S. P. Jiang, J. Mater. Sci., 200
Page 207 and 208:
References 73 T. J. Toops, D. B. Sm
Page 209 and 210:
References 98 G. W. Coffey, J. Hard
Page 211 and 212:
References 123 A. Laachir, V. Perri
Page 213 and 214:
References 147 C. Lu, T. Z. Sholkla
Page 215 and 216:
References 171 K. Adams, J. Cavatai
Page 217 and 218:
Appendix A Appendix A The article
Page 219 and 220:
temperature and in the presence of
Page 221 and 222:
Table 1 Energy intervals and step s
Page 223 and 224:
Figure 5 Impedance spectra, Nyquist
Page 225:
Knibbe, R., Hauch, A., Hjelm, J., E
show all

Electrochemical reduction of NOx - DTU Orbit

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?