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Al2O3 catalyst for diesel applications
Science and Technology in Catalysis 2002 Copyright 9 2003 by Kodansha Ltd.
457
101
Development of deNOx Catalyst Based on Ag/AIzO3 Catalyst for Diesel Applications
Ken Nagashima ~, Makoto Nagata', Katsuaki Katoh 1, Kengo Soda2 and Masashi Sugiyama 2 ' N.E. Chemcat Corporation, 678 Ipponmatsu, Numazu, Shizuoka, 410-0312, Japan 2 Sumitomo Metal Mining CO., LTD., 3-18-5 Nakakokubu, Ichikawa, Chiba, 272-8588, Japan Abstract Ag/A120 3 was studied as a HC-SCR (Hydrocarbon - Selective Catalytic Reduction) catalyst for diesel application[ 1-2]. Performance requirement of this catalyst is high NOx conversion with high thermal durability and sulfur resistance. The Ag/AI203 system was improved by addition of additives. To study the improvement effect, the interactions between the HC-SCR and the catalysts were investigated by TG/DTA. DTA measurement results showed that HC/O2 reaction was restrained in the improved catalyst. This result suggests that there was sufficient HC (diesel fuel) for NOx reduction on the improved catalyst. 1. INTRODUCTION Several types of de-NOx catalysts are under investigation to meet the coming new diesel regulation : NSR (NOx Storage & Reduction), Urea-SCR (ex. Zeolite), and HC-SCR (ex. Ir and Ag/A1203, etc). Ag/AI203 catalyst shows a highly selective de-NOx performance in the presence of HC under lean conditions. In this work, the addition of additives (B, C and D) to the Ag/A1203 catalyst was studied to improve de-NOx performance. The mechanism of improvement was studied from the view of the interactions between HC and the catalyst. 2. EXPERIMENTAL Ag/AI203 catalyst (the original) and the catalyst with additives (B, C and D) were prepared by impregnation. Catalysts were coated on the honey-comb monolithic substrate (NGK 400cpsi/6mill). 5L catalyst (7.5 inch diameter and 3.5 inch L (2 pcs)) was used for the engine test. Catalytic activity was evaluated by 2L N.A. diesel engine with low sulfur diesel fuel (50 ppm sulfur). In D 13 mode evaluation, extra HC (diesel fuel) was added into the inlet exhaust pipe of the catalyst. Interaction between HC and catalyst (HC adsorption/desorption, HC oxidation and NO/HC reaction) was evaluated by TG/DTA. To imitate the extra diesel fuel injection effect, Ag/AI203 catalyst powder was mixed with 10wt% of diesel fuel (S-50 ppm) in this measurement. 90 ~ A I 2 0 3
3. RESULTS & DISCUSSION 3. 1. DeNOx performance evaluation Figure 1 shows the deNOx performance of D 13 mode repetition evaluation when the catalyst is fresh. Sample C showed improvement of deNOx performance (>55% initially). Sample C showed about 50% NOx conversion even after the 10th D I3 mode evaluation repetition.
"E 60
a
,,,
1
2
Simple B 'Simple O 'xSlmphl D
-
--
-
u 40 30
z
0
3
4
5 6 7 $ 9 10 i1 12 13 14 15 le D13 mode repot,~.iontJnle|
Fig. 1 DeNOx performance by D13 mode evaluations.
458 K. Nagashima et al. Light-on and light-off deNOx performance is shown in Fig. 2. Ag/A1203 100 (original) showed hysteresis (ex. 20% .... ~ t 90 conversion difference at 350 ~ ). This phenomenon was assumed to be caused by adsorbed HC on the catalyst. The not-reacted HC (with oxygen or NOx) may cover the active site of the Ag/A1203 catalyst. In the improved catalyst (sample C) evaluation 20 ~" results, large hysteresis was not observed. 10 "-I * -A~Ai2Oa0:~np up) ,-.1~,M//~t203(Ramp-am ._~.-Sample O (Ramp up) ~ Sample0 ('Ramp down) I I 3. 2. Interaction of HC and Ag/AI203 catalyst 200 250 300 350 400 4,50 500 550 Temperatum/C HC/O 2 and HC/NO reactions were evaluated by TG-DTA. In 10% oxygen/He Fig. 2 Temperature window of NOx conversion. atmosphere (Fig. 3), exothermic heat in Conditions' HC/NOx--5, SV=15,000h-1, 2L diesel sample C was restrained compared to the engine(NA). original catalyst. It suggested that HC oxidation was promoted more on Ag/A1203 (original) catalyst. In 500 ppm NO/He atmosphere (Fig. 4), however, exothermic heat in sample C was higher than that in the original catalyst. These results suggest that the HC/O2 reaction was promoted on Ag/AI203 catalyst, so sufficient HC for NOx reduction could not exist on the Ag/A1203 catalyst. On the other hand, sufficient of HC for NOx reduction was supplied in sample C because of its low HC/O2 reaction. Instead of HC/O2, NO/HC reaction was promoted on sample C. In other words, sample C is able to use HC effectively in the NO reactions especially under low O 2 concentration. It was suggested that HC/NO reaction promoted and produced intermediate species, such as isocyanate (-NCO), in sample C [3-4]. Addition of additive C is assumed to have an effect on the production or stabilization of isocyanate.
i
2
OZ/Ha w/10~iasel fuel (S=50ppm)
.
~
!.5 ".g. 1
[1=1
o.5
0
-0.5
0 Tqnl~r.turo (C)
Fig. 3 DTA analysis of HC/O2 reaction on Ag/A1203 catalyst. Feed: 10%O2, He balance. Sample was mixed with diesel fuel (S=50 ppm).
100
200
300 400 "l'omporature (C)
500
600
Fig. 4 DTA analysis of HC/NO reaction on Ag/AI203 catalyst. Feed: 500 ppm NO, He balance. Sample was mixed with diesel fuel (S--50 ppm).
ACKNOWLEDGEMENT The authors wish to thank Dr. Stanley A. Roth of the Engelhard Corporation for his contribution and support of this study. REFERENCES [ 1] T. Miyadera and K. Yoshida, Chem. Lett., 1993, 1483. [2] T. Miyadera, Appl. Catal. B, 1993, 2, 199. [3] S. Sumiya, H. He, A. Abe, N. Takezawa, K. Yoshida, J. Chem. Soc., Faraday Trans., 1998, 94(15), 2217. [4] T. Miyadera, Appl. Catal. B, 1997, 13, 157.
457
101
Development of deNOx Catalyst Based on Ag/AIzO3 Catalyst for Diesel Applications
Ken Nagashima ~, Makoto Nagata', Katsuaki Katoh 1, Kengo Soda2 and Masashi Sugiyama 2 ' N.E. Chemcat Corporation, 678 Ipponmatsu, Numazu, Shizuoka, 410-0312, Japan 2 Sumitomo Metal Mining CO., LTD., 3-18-5 Nakakokubu, Ichikawa, Chiba, 272-8588, Japan Abstract Ag/A120 3 was studied as a HC-SCR (Hydrocarbon - Selective Catalytic Reduction) catalyst for diesel application[ 1-2]. Performance requirement of this catalyst is high NOx conversion with high thermal durability and sulfur resistance. The Ag/AI203 system was improved by addition of additives. To study the improvement effect, the interactions between the HC-SCR and the catalysts were investigated by TG/DTA. DTA measurement results showed that HC/O2 reaction was restrained in the improved catalyst. This result suggests that there was sufficient HC (diesel fuel) for NOx reduction on the improved catalyst. 1. INTRODUCTION Several types of de-NOx catalysts are under investigation to meet the coming new diesel regulation : NSR (NOx Storage & Reduction), Urea-SCR (ex. Zeolite), and HC-SCR (ex. Ir and Ag/A1203, etc). Ag/AI203 catalyst shows a highly selective de-NOx performance in the presence of HC under lean conditions. In this work, the addition of additives (B, C and D) to the Ag/A1203 catalyst was studied to improve de-NOx performance. The mechanism of improvement was studied from the view of the interactions between HC and the catalyst. 2. EXPERIMENTAL Ag/AI203 catalyst (the original) and the catalyst with additives (B, C and D) were prepared by impregnation. Catalysts were coated on the honey-comb monolithic substrate (NGK 400cpsi/6mill). 5L catalyst (7.5 inch diameter and 3.5 inch L (2 pcs)) was used for the engine test. Catalytic activity was evaluated by 2L N.A. diesel engine with low sulfur diesel fuel (50 ppm sulfur). In D 13 mode evaluation, extra HC (diesel fuel) was added into the inlet exhaust pipe of the catalyst. Interaction between HC and catalyst (HC adsorption/desorption, HC oxidation and NO/HC reaction) was evaluated by TG/DTA. To imitate the extra diesel fuel injection effect, Ag/AI203 catalyst powder was mixed with 10wt% of diesel fuel (S-50 ppm) in this measurement. 90 ~ A I 2 0 3
3. RESULTS & DISCUSSION 3. 1. DeNOx performance evaluation Figure 1 shows the deNOx performance of D 13 mode repetition evaluation when the catalyst is fresh. Sample C showed improvement of deNOx performance (>55% initially). Sample C showed about 50% NOx conversion even after the 10th D I3 mode evaluation repetition.
"E 60
a
,,,
1
2
Simple B 'Simple O 'xSlmphl D
-
--
-
u 40 30
z
0
3
4
5 6 7 $ 9 10 i1 12 13 14 15 le D13 mode repot,~.iontJnle|
Fig. 1 DeNOx performance by D13 mode evaluations.
458 K. Nagashima et al. Light-on and light-off deNOx performance is shown in Fig. 2. Ag/A1203 100 (original) showed hysteresis (ex. 20% .... ~ t 90 conversion difference at 350 ~ ). This phenomenon was assumed to be caused by adsorbed HC on the catalyst. The not-reacted HC (with oxygen or NOx) may cover the active site of the Ag/A1203 catalyst. In the improved catalyst (sample C) evaluation 20 ~" results, large hysteresis was not observed. 10 "-I * -A~Ai2Oa0:~np up) ,-.1~,M//~t203(Ramp-am ._~.-Sample O (Ramp up) ~ Sample0 ('Ramp down) I I 3. 2. Interaction of HC and Ag/AI203 catalyst 200 250 300 350 400 4,50 500 550 Temperatum/C HC/O 2 and HC/NO reactions were evaluated by TG-DTA. In 10% oxygen/He Fig. 2 Temperature window of NOx conversion. atmosphere (Fig. 3), exothermic heat in Conditions' HC/NOx--5, SV=15,000h-1, 2L diesel sample C was restrained compared to the engine(NA). original catalyst. It suggested that HC oxidation was promoted more on Ag/A1203 (original) catalyst. In 500 ppm NO/He atmosphere (Fig. 4), however, exothermic heat in sample C was higher than that in the original catalyst. These results suggest that the HC/O2 reaction was promoted on Ag/AI203 catalyst, so sufficient HC for NOx reduction could not exist on the Ag/A1203 catalyst. On the other hand, sufficient of HC for NOx reduction was supplied in sample C because of its low HC/O2 reaction. Instead of HC/O2, NO/HC reaction was promoted on sample C. In other words, sample C is able to use HC effectively in the NO reactions especially under low O 2 concentration. It was suggested that HC/NO reaction promoted and produced intermediate species, such as isocyanate (-NCO), in sample C [3-4]. Addition of additive C is assumed to have an effect on the production or stabilization of isocyanate.
i
2
OZ/Ha w/10~iasel fuel (S=50ppm)
.
~
!.5 ".g. 1
[1=1
o.5
0
-0.5
0 Tqnl~r.turo (C)
Fig. 3 DTA analysis of HC/O2 reaction on Ag/A1203 catalyst. Feed: 10%O2, He balance. Sample was mixed with diesel fuel (S=50 ppm).
100
200
300 400 "l'omporature (C)
500
600
Fig. 4 DTA analysis of HC/NO reaction on Ag/AI203 catalyst. Feed: 500 ppm NO, He balance. Sample was mixed with diesel fuel (S--50 ppm).
ACKNOWLEDGEMENT The authors wish to thank Dr. Stanley A. Roth of the Engelhard Corporation for his contribution and support of this study. REFERENCES [ 1] T. Miyadera and K. Yoshida, Chem. Lett., 1993, 1483. [2] T. Miyadera, Appl. Catal. B, 1993, 2, 199. [3] S. Sumiya, H. He, A. Abe, N. Takezawa, K. Yoshida, J. Chem. Soc., Faraday Trans., 1998, 94(15), 2217. [4] T. Miyadera, Appl. Catal. B, 1997, 13, 157.