1. 2 National Chemical Laboratory, 411008 Pune, India
Deposition-precipitation versus anionic exchange Au/Al2O3 catalysts: A comparative investigation towards NOx SCR
D. -L. Nguyen*, 1, J. -S. Girardon1, C. Dujardin1, C. Lancelot1, S. Umbarkar2, M. -K. Dongare2, P. Granger1
1 Unité de Catalyse et de Chimie du Solide, USTL, Villneuve d’Ascq, France
2 National Chemical Laboratory, Pune, India
Lady and Gentlemen. Today, I'm glad to present to you my talk which entitles promising performance of gold-based catalyst for NO SCR by hydrocarbons in lean burn condition. My work was performed in UCCS, in Lille, France in collabration with national chemical laboratory in Pune, India.
Lille, July, 2012

2. Introduction (1) => Reduction of the NOx emission
Road vehicles
Agriculture/sylviculture
Residential
Industry
Energy transformation
Other transports
Evolution of Diesel engine regulations
Norm
Component CO
NOx
HC+NOx
Euro 5 (2009)
Limit (mg/km)
500
180
230
Euro 6 (2014) - 80
170
As you know, with the development of society and industry, the emission of toxic gases such as CO, NOx, SOx, is very important. Within these gases, NOx, resulted essentially from transport with 52% of NOx emission sources, is very harmful for human and environement, acid rain, ground ozone for example.
More over, the specifications concerning the emission of NOx are more and more strict. Euro 6 limit NOx emission to 80 mg/km for diesel engine
=> It’s necessary to decrease NOx from diesel motor.
New restrictions (1)
=> Reduction of the NOx emission
(1)
Lille, July, 2012

3. Introduction (2) Lean NOx Trap technology (Toyota 1993)
Pt/BaO/Al2O3 based catalyst
Fuel consumption
Deactivation and sensibility to sulphur
NH3-SCR
Fe-zeolite, vanadium-based catalyst
Additional urea tank
Solidification of urea in winter
NH3 slip
HC-SCR
often low selectivity
Simplest technology
From the decade 90, there were NOx traps based on Pt/BaO/Al2O3 but it showed many disadvantages such as fuel consumption or sensible to sulphur.
Second solution was applied is using NH3 SCR based on Fe/zeolithe or vanadium catalyst but these disadvantages were found such as addition of urea tank, NH3 slip
The third solution was using HC-SCR which showed rather low conversion but it was very simple to install in diesel engine.
Lille, July, 2012

4. Introduction (3)
Silver as an attractive solution for replacing noble metals?
720ppm NO+300ppm C3H ppm C7H8+7200ppm H2+ 4,3%O2+7,2% CO2+7,2% H2O +1ppm SO2 +He
NOx conversion (%)
Temperature (oC)
Initial
1pp SO2
1ppm SO2/SO3
Ag/Al2O3 was applied to reduce Nox emission by using this technique. Although better conversion of NOx, the catalyst was sensible to sulfur and quickly deactivated after ageing.
Wet impregnation using silver nitrate salt with the alumina precursor. Final catalyst (2 wt.% Ag/Al2O3) was obtained after successive drying overnight at 80 ◦C followed by calcination at 500 ◦C for 12 h.
Deactivation after thermal ageing2
Sensitive to sulfur 2
N2O formation
Ag/Al2O3 catalyst
2 J. P. Breen et al. / Applied Catalysis B: Environmental 70 (2007) 36–44
Lille, July, 2012

5. Introduction (4) Au: alternative catalyst to Ag/Al2O3 High selectivity
Large range of temperature
Temperature (K)
Conversion to ward N2 (%)
Au(0.17 wt%)/Al2O3+Mn2O3 (19 : 1 wt/wt)
Au(0.16 wt%)/Mn2O3
Mn2O3
3 A. Ueda, M. Haruta, Applied Catalysis B 18 (1998)
Improve activity of Au/Al2O3 by Mn2O3 addition 3
1000 ppm NO+1000 ppm C3H6 + 5% O2+ 10%H2O, GHSV: h-1 cm3/g
Au(0.17 wt%)/Al2O3
Au/Al2O3 was used as an alternative source to reduce NOx emission because of its excellent selectivity toward N2 and an large range of operating temperature.
Haruta et al revealed high conversion of NO toward N2 by using Au/Al2O3 seperately and mechanically mixed with Mn2O3
This demonstrated that this type catalyst was a promising solution for this purpose. But simple mixture was used to test catalytic activity. So we decided to developed gold-based catalyst supported on alumina for NOx reduction in the presence of reductants such as H2, C3H6, etc
Promising solution for NO conversion
Lille, July, 2012

6. Out line Introduction Synthesis Catalytic test Characterizations
Objective:
Comparison of various synthesis route in order to obtained selective catalysts having
High gold dispersion
High thermal ageing resistance
Introduction
Synthesis
Catalytic test
Characterizations
Conclusions
In this presentation, first i will talk about the introduction. Then I will continue with the catalysts preparation, their characterization. The catalytic activity and reductant behavior will be presented. I will finish by conclusions and prospects.
Lille, July, 2012

7. Catalysts synthesis (1)
Solution HAuCl4, 70°C
NaOH
pH=7
Filtration, washing
Stirring
Al2O3 (*)
Drying, 100°C
Calcination, 300oC, 4h, air
Deposition-precipitation with NaOH
Au/Al2O3 (DP)
Au/Al2O3 catalysts were prepared by several methods: Deposition precipitation with NaOH or Urea, direct anionic exchange with water or ammonia.
In DP with NaOH, HAuCl4 was first dissolved in distilled water and kept stirring at 70°C. NaOH solution was used to adjust pH to 7. Alumina was then added and the slurry was stirring in additional 1 h. The catalyst was obtained after washing, drying and calcination at 300°C in air.
A. Ueda et al, Appl. Catal, B 12 (1997) 81-93
Lille, July, 2012

8. Catalysts synthesis (2)
Anionic Exchange AE
Solution HAuCl4, 70oC
Filtration and washing
Drying, 100oC
Calcination, 300 , 4h, air
Al2O3
Stirring
Au/Al2O3 (AE)
In DAE method, alumina was added to HAuCl4 solution and kept stirring. After filtration and washing with water or ammonia, the solid was calcined at 300°C, under air, for 4 h.
The catalysts was nominated DP, DAE respectively.
S. Ivanova et al. , Applied Catalysis A: General 298 (2006) 57–64
Lille, July, 2012

9. Catalytic test (1) Pre-treatement (1):
0.03%NO+0.03%CO+0.03%C3H6+0.2%H2+0.01%C10H22+10%O2+10%CO2+5%H2O+He
Pre-treatement (1):
TPR1 after pre-treatment and TPR2 after overnight thermal ageing (2)
dT/dt = 2°C.min-1
GHSV = h-1
Figure 1: TPR protocol
Each catalyst was checked with respect to fresh and aged state that we called TPR1 and TPR2. First, it was pretreated under H2 flow at 250°C overnight and then followed by TPR1. Seconde TPR was performed after ageing at 500°C under reaction mixture. Temperature rampe = 2°C/min
Space velocity = mL.h-1.g-1
Typical gas mixture was used with the presence of reductants (CO, propylene, H2 and decane), inhibitants (CO2, H2O, O2)
Lille, July, 2012

10. Catalytic test (2) DP AE (300) Two domains of conversion
Significant formation of N2O
Thermal ageing induces a loss of NOx conversion
Extra production of CO => partial oxidation of decane and/or reforming reaction
Start at higher temperature
More selective to N2
Beneficial effect after thermal ageing
Two domains of conversion
Significant formation of N2O
Thermal ageing induces a loss of NOx conversion
Extra production of CO => partial oxidation of decane and/or reforming reaction
Start at higher temperature
More selective to N2
Beneficial effect after thermal ageing => increasing of relative gold concentration
Figure 2. Catalytic activity of fresh (open symbol) and aged (full ) samples
Lille, July, 2012

11. Nitrogen physisorption
Characterization (1)
Catalyst
Nitrogen physisorption
SSA (m2.g-1)
dpore (nm)
Au/Al2O3 (DP)
Fresh
395
3.5
Aged
206
6.4
Au/Al2O3 (AE) 300°C
361
181
7.0
Table 1: Surface properties of fresh and aged samples
Mesoporous material with high specific area and narrow pore diameter
Ink-bottle pores type
Larger cylindrical pores type
SSA , dpore => opening of pores during thermal ageing
Structure reconstruction during catalyst synthesis
Mesoporous material with high specific area and narrow pore diameter
Larger pores
SSA , dpore => opening of pores during thermal ageing
Lille, July, 2012

12. Characterization (2) DP
Figure 4. XRD of fresh and aged catalysts
a) AuDAE(300) fresh; b) AuDEA(300) aged; c) AuDP fresh; d) AuDP aged DP AE
Presence of boehmite phase after calcination at 300°C
Boehmite transformed to g-alumina phase
Structure reconstruction during catalyst test
Observation of gold in AE samples <=> larger particle size
Resistance to sintering
Presence of boehmite phase after calcination at 300°C
Boehmite transformed to g-alumina phase
Evidence observation of gold in AE samples <=> larger particle size
More open porous structure
Resistance to sintering AE > DP
Lille, July, 2012

13. Characterization (3) Catalyst Elemental analysis XPS analysis Au (wt%)
IAu/IAl
Au4f7/2 (eV)
Au/Al2O3 (DP)
Fresh
0.52
1.7x10-2
84.2
Aged
0.8x10-2
83.7
Au/Al2O3 (AE) 300°C
0.76
2.7x10-2
84.1
4.0x10-2
83.8
Table 2: Elemental and XPS analysis of fresh and aged catalysts
Metallic gold observed on calcined samples
Shift eV observed on aged catalysts  extent of metal/support interactions with reduced coordination number of Au atoms
Au%wt (AE) > Au%wt (DP)
Metallic gold observed on calcined samples
Shift 0.3 eV observed on aged catalyst
Higher gold concentration of aged catalyst => redispersion of gold nanoparticles
Lille, July, 2012

14. Conclusions Higher gold loading and dispersion obtained by AE method.
Stability AE > DP
Structure reconstruction during catalyst test
Redispersion of gold particle during thermal ageing
Structure reconstruction during catalyst synthesis
Higher gold loading and dispersion obtained by AE method.
Stable after thermal ageing
Redispersion of gold particle during thermal ageing
Lille, July, 2012

15. Thank you for your kind attention
CNRS
NCL
Arnaud Beaurain
Martine Tressentaux
Anne-Sophie Mamede
Thank you for your kind attention
Lille, July, 2012

16. Lille, July, 2012

17. Lille, July, 2012

18. Catalytic test (3) AE (500) DP AE (300)
Figure 3: H2 and C3H6 conversion DP
AE (300)
H2 converted at low temperature
Conversion delayed after ageing => NO/H2 reaction would not be promoted
Propene seems more selective and would be likely involved in the preferential reduction of NO to nitrogen
H2 converted at low temperature
Conversion delayed after ageing => NO/H2 reaction would not be promoted
Propene seems more selective and would be likely involved in the preferential reduction of NO to nitrogen
H2 converted at higher temperature
Conversion hastened after ageing
H2 converted at higher temperature
Conversion hastened after ageing
Lille, July, 2012