Urea/SCR Technology for removing NOx from Diesel Engine

Transcription

1 CLEERS 211 Workshop (Apr , 211) Urea/SCR Technology for removing NOx from Diesel Engine Apr. 19, 211 In-Sik Nam POSTECH Environmental Catalysis Laboratory (PECL) Department of Chemical Engineering/ School of Environmental Science and Engineering POSTECH

2 Table of contents I. Introduction II. Urea/SCR Catalysts (Part A) i) Promising Low-Temperature Urea/SCR catalyst ii) Deactivation of Urea/SCR catalysts iii) Fast SCR reaction III. Reaction Kinetics (Part B) i) Urea decomposition kinetics ii) NH 3 /SCR and Urea/SCR kinetics for CuZSM5 iii) Monolith reactor model for CuZSM5 iv) Transient model IV. Summary & Prospective

3 NOx emission standards Emission standard for the diesel engine PM [g/km] US Europe NOx [g/km] NOx [g/km] Japan China PM [g/km] Hackenberg et al., SAE,

4 DeNOx technologies Technology Catalysts Features Limitations LNT - Pt/Ba/Al 2 O 3 - Cyclic operation - Wide temperature window - High activity - No infrastructure problem - Periodic regeneration - Sulfur tolerance - High noble metal loading - Low temperature activity HC/SCR - Ag/Al 2 O 3 - Pt/zeolite - Cu/zeolite - Simple engine control - Continuous operation - HC (fuel) as reductant - No infrastructure problem - Coking and HC slip - Low temperature activity - Poor durability and sulfur tolerance - High fuel economy penalty Urea/SCR - Cu,Fe/zeolite - V 2 O 5 /TiO 2 - Mn/TiO 2 - Simple engine control - Urea as reductant - Wide temperature window - High activity - Mostly non-nm catalysts - Onboard urea tank / urea freezing - Urea infrastructure - NH 3 /HC slip - Public perception on the use of he avy metals including Cu & V as a cat alytic component

5 Superior denox performance of Urea/SCR technology 1 NOx Conversion (%) Urea SCR NOx Storage Catalyst HC SCR Catalysts Cu/ZSM5 2 Pt/Alumina Temperature (C) Personal Communication with Dr. Se Oh, GM R&D center

6 SCR by Urea l Decomposition of urea Thermal decomposition H 2 N-CO-NH 2 (s) NH 3 (g) + HNCO(g) Hydrolysis of isocyanic acid HNCO(g) + H 2 O(g) NH 3 (g) + CO 2 (g) Overall reaction H 2 N-CO-NH 2 (s) + H 2 O(g) 2NH 3 (g) + CO 2 (g) l Urea/SCR 4NH 3 (g) + 4NO (g) + O 2 (g) 4N 2 (g) + 6H 2 O (g) 2H 2 N-CO-NH 2 (s) + 4NO(g) + O 2 (g) 4 N 2 (g) + 4H 2 O(g) + 2CO 2 (g) Engine DOC DPF SCR option NH 3 Urea injector

7 Part A. Urea/SCR Catalysts i) Promising Eco-Friendly Urea/SCR catalysts ii) Deactivation of Urea/SCR catalysts iii) Fast SCR reaction

8 DeNOx performance over representative Urea/SCR catalysts Catalyst: CuZSM5, FeZSM5 and V 2 O 5 -WO 3 /TiO 2 Feed: 1, ppm NO, Variable amounts of NH 3 (1 ppm NH 3 slip), 1 % O 2, 5 % H 2 O and N 2 balance Reactor SV: 52, h -1 CuZSM5 V 2 O 5 -WO 3 /TiO 2 FeZSM5 Kröcher et al., Stud. Surf. Sci. Catal., 171 (27) 261.

9 CuCHA for the Urea/SCR technology Catalysts: CuSSZ13, CuBEA and CuZSM5 Feed: 35 ppm NO, 35 ppm NH 3, 14 % O 2, 2 % H 2 O and N 2 balance Reactor SV: 3, h -1 Catalysts: Cu(2.9)SSZ13, Cu(3.8)SSZ16 and Cu(2.9)ZSM5 Feed: 5 ppm NO, 5 ppm NH 3, 1 % O 2, % H 2 O and N 2 balance Reactor SV: 42,5 cc/(h gcat) à about 23, h -1 Fickel et al., Appl. Catal. B, 12 (211) 441. Kwak et al., J. Catal., 275 (21) 187.

10 Promising Eco-Friendly Low Temperature Urea/SCR catalyst l Demand for ECO-friendly catalyst over Urea/SCR Ø The most common Urea/SCR catalysts using Heavy Metals CuZSM5 catalyst à Best low temperature catalyst V 2 O 5 /TiO 2 catalyst à Most common commercial SCR catalyst for stationary source of NOx ü Public Perception on Heavy Metals Cu: cause of the disease of copper imbalance (Wilson s disease, Dioxin.. Etc) Kim et al., Nat. Chem. Biol., 4 (28) 176 V 2 O 5 : toxicity and discharge from tail pipe (low melting point) Li et al., Chem. Commun., 12 (28) 147 l Mn-based SCR catalyst Ø A representative low temperature SCR catalyst, especially for the removal of NO x from stationary sources [Pena et al., J. Catal., 221 (24) 421] Ø Mn is commonly recognized as a less toxic metal compared to Cu, Ni and V [H. Hasan, Manganese, First ed, The Rosen Publishing Group, New York, 28, pp. 31] Mn-based catalyst may be a new ECO-friendly Urea/SCR catalyst.

11 Schematic Flow Diagram of NH 3 (or Urea)/SCR Reactor System Reaction Condition Gas composition : 5 ppm NOx, 5 ppm NH 3 (or 25 ppm urea), 5% O 2, 1 % H 2 O and N 2 balance Reactor SV: 1, ~ 4, h -1 Reaction temperature : 15 ~ 5 o C

12 DeNOx performance & N 2 selectivity over Mn-Fe catalysts Catalyst: Mn-Fe/ZSM5, Mn-Fe/TiO 2, Mn-Fe/Al 2 O 3 (impregnation) Mn-Fe/TiO 2 (sol-gel), CuZSM5 (ion-exchange) Reaction condition: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance. Reactor SV: 1, hr -1 Low-temperature SCR catalyst N 2 selectivity= [(Conversion of NO+NH 3 )-(formation of N 2 O+NO 2 )] / (Conversion of NO+NH 3 ). US Pat. Appl., 12/628,37 ( ), Eur. Pat. Appl., ( ), Kor. Pat. Appl., , ( ) Mn-Fe/ZSM5 catalyst shows excellent denox activity, N 2 selectivity and wider operating temperature window, compared to Mn-Fe/TiO 2 and Mn/Al 2 O 3 catalysts.

13 XPS spectra and atomic concentration of Mn Low-temperature SCR catalyst Catalysts: Mn-Fe/ZSM5, Mn-Fe/TiO 2, Mn-Fe/Al 2 O 3 (impregnation) Mn-Fe/TiO 2 (sol-gel), MnO 2 (reference), Mn 2 O 3 (reference) Atomic surface concentrations obtained by XPS spectra Catalyst Mn Fe Al Si Ti Mn-Fe/ZSM Mn-Fe/TiO 2 (sol-gel) Mn-Fe/TiO Mn-Fe/Al 2 O Mn over Mn-Fe based catalysts exists in a form of Mn 4+, regardless of the catalysts. More Mn 4+ exists on the surface of Mn-Fe/ZSM5 and Mn-Fe/TiO 2 (sol-gel) catalysts compared to M n-fe/tio 2 & Al 2 O 3 prepared by impregnation method.

14 NH 3 -TPD study over Mn-Fe catalysts Low-temperature SCR catalyst Catalysts: Mn-Fe/ZSM5, Mn-Fe/TiO 2, Mn-Fe/Al 2 O 3 (impregnation), Mn-Fe/TiO 2 (sol-gel) Mn-Fe/ZSM5 catalyst shows much larger capacity of NH 3 adsorption, compared to th e Mn-Fe/TiO 2 and Mn-Fe/Al 2 O 3 catalyst.

15 DeNOx performance over potential Urea/SCR Catalysts Feed condition: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance Reactor SV: 1, h -1 Low-temperature SCR catalyst US Pat. Appl., 12/628,37 ( ) Eur. Pat. Appl., ( ) Kor. Pat. Appl., ( ) Top. Catal., 3-31 (24) 37. Catal. Today, 151 (21) 244.

16 Deactivation of Urea/SCR catalysts Configuration of diesel after-treatment system HCs (Engine out) C 1 : 35~ 78 ppm Urea(NH 3 )/SCR 기술 CO, HCs, NOx, SO 2, soot High temp. exhaust HCs (DOC out) C 1 : 8~14 ppm, CO 2, NO 2, etc High temp. exhaust Han et al., J. Eng. Gas. Turb. Power., 18 (28) Hydrothermal stability - Hot exhaust gas stream - Top. Catal. 3/31 (24) 37 and J. Catal. 24 (26) 47. Sulfur tolerance - Sulfur contained in fuel - Catalysis 16 (22) 236. Hydrocarbon poisoning - HC slip from diesel engine - Micropor. Mesopor. Mater., 141 (211) 8 and Montreuil et al., SAE,

17 Hydrothermal stability of Urea/SCR catalysts Catalysts: CuZSM5, FeZSM5 and V 2 O 5 -WO 3 /TiO 2 catalysts Feed: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance Reactor SV: 1, h -1 Aging condition: aged in air flow with 1% H 2 O at 7 o C for 5 and 24 h Hydrothermal stability Conversion of NO (%) Conversion of NO (%) Conversion of NO (%) Reaction Temperature ( o C) Reaction Temperature ( o C) Reaction Temperature ( o C) CuZSM5 FeZSM5 V 2 O 5- WO 3 /TiO 2

18 Cause for thermal deactivation Dealumination of ZSM5 ~ Removal of the tetrahedral Al 3+, ~ The structural collapse of the zeolite Hydrothermal stability CuZSM5 Yan et al., J. Catal. 161 (1996) 43. Transformation of Cu 2+ ion Cu 2+ CuO or Cu 2 O By loss of the Cu out of the lattice and its ag glomeration (over-exchanged CuZSM5) Migration of Cu 2+ ion By migration of Cu 2+ species to another location in ZSM5 where they are stabilized and become less active (under-exchanged CuZSM5) Under exc hanged over excha nged J. Catal., 24 (26) 47. CuO 8 o C aged 7 o C aged 6 o C aged Fresh(CuZSM5) (Inaccessible site) 8 o C aged 7 o C Fresh (CuZSM5) Migration of Cu 2+ Square planar Another 2 sites Square pyramidal (inactive site) (Accessible site) (Inaccessible site) J. Catal., 24 (26) 47. Tanabe et al., Appl. Catal. B, 6 (1995) 145.

19 Cause for thermal deactivation Hydrothermal stability FeZSM5 V 2 O 5- WO 3 /TiO 2 Reduction of acidity by dealumination of Fe-ZSM5 ~ decrease of Brønsted acidity attributed to ammonia storage NMR (a) Fresh (b) Dry aged (at 65 o C) (c) Wet aged (at 65 o C) Brønsted acidity Phase transition of TiO 2 ~ Anatase à Rutile phase of TiO 2 Formation of crystalline V 2 O 5 ~ Transformation of monomeric vanadyl species in to crystalline V 2 O 5 Aged at 6 o C for 24h Krocher et al., Appl. Catal. B, 66 (26) 28. Catal. Today, 111 (26) 242.

20 Hydrothermal stability of CuCHA Hydrothermal stability Catalysts: Cu(2.9)SSZ13 and Cu(3.8)ZSM5 catalysts Feed: 5 ppm NO, 5 ppm NH 3, 1 % O 2 and N 2 balance Reactor SV: 42,5 cc/(h gcat) à about 23, h -1 Aging condition: aged in N 2 balance with 5% H 2 O and 1% O 2 at 75 o C for 3 or 7 h CuSSZ13 CuZSM5 Fickel et al., Appl. Catal. B, 12 (211) 441. Dealumination: extraction of Al 3+ [Al(OH) 3 : 5.3 Å] The Al(OH) 3 unit cannot exit the pores of the SSZ13 framework [SSZ: 3.8 Å, ZSM5: 5.5 Å] à Reincorporation of Al(OH) 3 into the SSZ13 framework when the catalyst was cooled down.

21 SEM images (before/after hydrothermal aging) Hydrothermal stability (a) (b) CuZSM5 (a) before aging (b) after aging (c) (d) CuSSZ13 (c) before aging (d) after aging Fickel et al., Appl. Catal. B, 12 (211) 441. The surface of CuZSM5 catalyst becomes rough upon the hydrothermal treatment, whereas the structural and morphological changes were hardly observed over CuSSZ13.

22 Hydrothermal stability Hydrothermal stability of the Mn-Fe/ZSM5 based and CuCHA catalysts Catalysts: Mn-Fe/ZSM5, Mn-Fe-REM/ZSM5 and CuCHA catalysts Feed: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance Reactor SV: 1, h -1 Aging condition: aged in air flow with 1% H 2 O at 65 o C for 24 h US Pat. Appl., 12/628,37 ( ), Eur. Pat. Appl., ( ), Kor. Pat. Appl., , ( )

23 XRD patterns of the Mn-Fe/ZSM5 based catalysts Hydrothermal stability XRD patterns The peaks attributed to the Mn 2 O 3 over the aged Mn-Fe-REM/ZSM5 catalyst are much weaker compared to the aged Mn-Fe/ZSM5 catalyst à The transformation of MnO 2 to Mn 2 O 3 may be moderated upon the addition of REM.

24 Sulfur poisoning over Urea/SCR catalysts SO 2 poisoning Mechanism I Mechanism II SO 2 + O 2 SO 3 SO 2 + O 2 SO 3 NH 3 + SO 3 (NH 4 ) 2 SO 4 or NH 4 HSO 4 M + SO 3 MSO 4 (metal sulfate) Al 2 O 3 + SO 3 Al 2 (SO 4 ) 3 Decomposed in higher temp. range (>7 o C) TGA BET Surface area ü Decomposition Temp: NH 4 HSO 4 (4 o C), (NH 4 ) 2 SO 4 (23 o C) and Al 2 (SO 4 ) 3 (77 o C) ü Surface area was decreased as sulfur content increased Catal. Today 11 (1992) 611.

25 Sulfur tolerance of Urea/SCR catalysts Catalyst: Mn-Fe/ZSM5, Mn-Fe-REM/ZSM5, CuCHA and CuZSM5 Feed: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O, 1 or 2ppm SO 2 and N 2 balance Reactor SV: 1, h -1 ; Reaction Temperature: 2 o C SO 2 poisoning TG 2MnO 2 à Mn 2 O 3 +.5O 2 SO 2 on SO 2 off Decomposition of MnSO 4 2MnO 2 à Mn 2 O 3 +.5O 2 post-treatment at 5 o C for 2h Decomposition of MnSO 4 MnSO 4 is decomposed ov er than 75 o C

26 C 3 H 6 inhibition Retardation of NH 3 /SCR performance by C 3 H 6 Catalysts: CuZSM5, FeZSM5 and V 2 O 5 -WO 3 /TiO 2 Feed composition: 5 ppm NO, 5 ppm NH 3, 5 or 2, ppm C 3 H 6, 5 % O 2, 1 % H 2 O and N 2 balance GHSV: 1, h -1 CuZSM5 FeZSM5 V 2 O 5- WO 3 /TiO 2 Micropor. Mesopor. Mater., 141 (211) 8.

27 C 3 H 6 inhibition Cause for retardation of NH 3 /SCR by C 3 H 6 TPD FT-IR (gas) -C N V 2 O 5- WO 3 /TiO 2 1. By competitive adsorption of NH 3 and C 3 H 6, denox activity decreases. 2. NH 3 is uselessly consumed by side rea ctions. FT-IR (surface) Absorbance (a.u.) 3 C3H6+NH3+NO+O2 C3H6+NH3+NO C3H6+NH3 C3H6 224 (-C N) 33 o C CuZSM Wavenumber/cm (carboxylate) Micropor. Mesopor. Mater., 141 (211) 8. Nanba et al., J. Mol. Catal. A-Gen., 276 (27) 13. < Ammoxidation reaction>: CH 2 =CHCH 3 + NH 3 + 3/2O 2 CH 2 =CHCN + 3H 2 O (acrylonitrile) CH 2 =CHCN+O 2 COx+HCN

28 Retardation of SCR activity by C 3 H 6 over Mn-Fe/ZSM5 based catalysts and CuCHA C 3 H 6 inhibition Catalysts: Mn-Fe/ZSM5, Mn-Fe-REM/ZSM5 and CuCHA Feed composition: 5 ppm NO, 5 ppm NH 3, 5 or 2, ppm C 3 H 6, 5 % O 2, 1 % H 2 O and N 2 balance GHSV: 1, h -1 Mn-Fe/ZSM5 Mn-Fe-REM/ZSM5 CuCHA

29 Effect of NO 2 /NOx ratio on denox performance Fast SCR reaction CuZSM5 FeZSM5 V 2 O 5- WO 3 /TiO 2 Conversion of NO or NO 2 (%) Conversion of NOx (%) > 3 o C 25 o C 2 o C (NO) (NO 2 ) Feed Ratio (NO 2 /NOx) > 3 o C 25 o C 2 o C 1 > 3 o C Maximum Feed Ratio (NO 2 /NOx) 25 o C 2 o C Conversion of NO or NO 2 (%) Conversion of NOx (%) o C 4 o C 35 o C 3 o C 25 o C 2 o C (NO) Feed Ratio (NO 2 /NOx) (NO 2 ) 45 o C 4 o C 35 o C 3 o C 25 o C 2 o C 1 45 o C 4 o C 35 o C Feed Ratio (NO 2 /NOx) 4NH 3 + 4NO + O 2 4N 2 + 6H 2 O (Standard SCR reaction) 4NH 3 + 2NO + 2NO 2 4N 2 + 6H 2 O (Fast SCR reaction) 4NH 3 + 3NO 2 3.5N 2 + 6H 2 O (NO 2 SCR reaction) Maximum 3 o C 25 o C 2 o C Conversion of NO or NO 2 (%) Conversion of NOx (%) o C 4 o C 35 o C 3 o C 25 o C 2 o C (NO) Feed Ratio (NO 2 /NOx) Feed Ratio (NO 2 /NOx) (NO 2 ) o C 4 o C 35 o C 3 o C 25 o C 2 o C 1 45 o C Maximum 4 o C 35 o C 3 o C 25 o C 2 o C Feed: 5 ppm NOx, 5 ppm NH 3, 5 % O 2,1 % H 2 O and N 2 balance; Reactor SV: 5, h -1 Stud. Sur. Sci. Catal., 159 (26) 441.

30 Fast SCR reaction SCR of NOx by NH 4 NO 3 for enhancing low-temperature SCR activity Catalysts: V 2 O 5 -WO 3 /TiO 2 and FeZSM5 catalysts Feed: 1, ppm NO or 5 ppm NO + 5ppm NO 2 (for Fast SCR), 1, ppm NH 3, 2 % O 2, 1 % H 2 O and N 2 balance Reactor SV: 33, h -1 FeZSM5 V 2 O 5 -WO 3 /TiO 2 Forzatti et al., Angew. Chem. Int. Ed., 48 (29) Forzatti et al., Ind. Eng. Chem. Res., 49 (21) NH 3 + 2NO + NH 4 NO 3 à 3N 2 + 5H 2 O Producing a key intermediate (HNO 3 ) in the Fast SCR reaction The optimal concentration of NO 2 for the Fast SCR reaction may not be guaranteed at low tempera ture region (<2 o C), due to the low NO oxidation activity of DOC. à Injection of NH 4 NO 3 solution to feed-stream may be an alternative strategy to resolve this issue.

31 Reaction mechanism of fast SCR Fast SCR reaction Catalyst: V 2 O 5 -WO 3 /TiO 2 Feed: 1, ppm NH 3, 1, ppm NO 2 or 1 ppm N O (when used), 1 % H 2 O in balance He Reactor SV: 1, h -1 ; Reaction Temperature: 17 o C NH 4 NO 3 +NO à NO 2 + N 2 +2H 2 O NO 2 +NH 3 à 1/2NH 4 NO 3 + 1/2N 2 + 1/2H 2 O Accumulation of NH 4 NO 3 Reaction of NH 4 NO 3 with NO and NH 3 Nova et al., Catal. Today, 114 (26) 3.

32 Part B. Reaction Kinetics for Urea/SCR i) Urea decomposition kinetics ii) Urea/SCR kinetics for CuZSM5 iii) Monolith reactor model for CuZSM5 iv) Transient model

33 Reaction Kinetics & Model prediction (Urea thermal decomposition) l Urea (H 2 N-CO-NH 2 NH 3 + HNCO) dcurea = k1curea dτ l HNCO dchnco = k1curea dτ l NH 3 dcnh 3 = k1curea dτ Concentration of Urea (ppm) model prediction 423 K 523 K 573 K 623 K 673 K 723 K Concentration of NH 3 (ppm) Concentration of HNCO (ppm) Residence Time (s) model prediction 423 K 523 K 573 K 623 K 673 K 723 K model prediction 423 K 523 K 573 K 623 K 673 K Residence Time (s) Feed: 25 ppm urea, 5 % O 2, 2 % H 2 O and N 2 balance SV: 45, ~ 2, h -1 (flow rate/volume of glass bead) Residence Time (s) Ind. Eng. Chem. Res. 43 (24) 4856.

34 Concentration (ppm) Feed: 25 ppm urea, 5 % O 2, 2 % H 2 O and N 2 balance; Thermal decomposition: 25 o C Catalyst: CuZSM5; After thermal decomposition: 25 ppm urea à 115 ppm urea, 11 ppm HNCO and 125 ppm NH Reaction Kinetics & Model prediction (Urea thermal decomposition & hydrolysis of HNCO) l Urea (H 2 N-CO-NH 2 NH 3 + HNCO) l HNCO (HNCO + H 2 O à NH 3 + CO 2 ) dcurea dchnco = k1curea = k1curea k2chncoch 2O dτ dτ l NH 3 dcnh3 = k1curea + k2chncoch 2O k3cnh3 dτ NH 3 oxidation Model Urea HNCO NH 3 Concentration (ppm) Model Urea HNCO NH Temperature ( o C) Temperature ( o C) T Therm = 25 o C, SV: 99, h -1 T Therm = 25 o C, SV: 99, h -1 Ind. Eng. Chem. Res. 43 (24) 4856.

35 Reaction Kinetics (NH 3 /SCR over CuZSM5) Dual Site Catalysis based upon LHHW mechanism l NO Reduction NO + S 1 NO S 1 NH 3 + S 2 NH 3 S 2 K NO K NH3 NO S 1 + NH 3 S 2 + O 2 N 2 S 1 + H 2 O S 2 k NO l NH 3 Oxidation NH 3 + S2 NH 3 S2 K NH3 NH 3 S2 + O 2 N 2 S2 + H 2 O S2 k NH3 dx kc (1 X )(1 X ) NO = dτ K C X K C X 1 NH3 NO NH3 {1 + NO NO (1 NO )}{1 + NH NH (1 NH )} dx k C (1 X )(1 X ) k (1 X ) NH3 1 NO NO NH3 2 NH3 = + τ {(1 + NO NO (1 NO )}{1 + NH NH (1 NH )} 1 + NH NH (1 NH ) d K C X K C X K C X Ind. Eng. Chem. Res.,45 (26) 526.

36 Model Prediction (NH 3 /SCR over CuZSM5) [Gas composition: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance; SV: 1, ~ 4, h -1 ] Conversion of NO (%) S.V.=1,h -1 Model Exp-NO Exp-NH NH 3 Slip (ppm) Conversion of NO (%) S.V.=2,h -1 Model Exp-NO Exp-NH NH 3 Slip (ppm) Reaction Temperature ( o C) Reaction Temperature ( o C) Conversion of NO (%) S.V.=3,h -1 Model Exp-NO Exp-NH NH 3 Slip (ppm) Conversion of NO (%) S.V.=4,h -1 Model EXP-NO EXP-NH NH 3 Slip (ppm) Reaction Temperature ( o C) Reaction Temperature ( o C) Ind. Eng. Chem. Res.,45 (26) 526.

37 Reaction Kinetics (Urea/SCR over CuZSM5) l Urea l HNCO l NO l NH 3 ) (1 3 Urea Urea X k d dx = τ ) (1 ) ( HNCO O H HNCO Urea Urea HNCO X C k C X C k d dx + = τ )} (1 )}{1 (1 {1 ) )(1 ( NH NH NH NO NO NO NH NO NH NO X C K X C K X X k C d dx + + = τ )} (1 )}{1 (1 {1 ) )(1 ( NH NH NH NO NO NO NH NO NO NH X C K X C K X X C k d dx + + = τ ) (1 ) (1 ) (1 1 ) (1 NH HNCO HNCO O H NH Urea Urea NH NH NH NH C X C C k C X C k X C K X k + +

38 Model Prediction (Urea/SCR over CuZSM5) Effect of thermal decomposition reactor temperature [Gas composition: 5 ppm NO, 25 ppm Urea, 5 % O 2, 1 % H 2 O and N 2 balance; SV: 1, h -1 ] Conversion of NO (%) (a) Exp-NO Exp-NH 3 Exp-Urea Exp-HNCO Model Slip of NH 3, Urea and HNCO (ppm) Conversion of NO (%) (b) Exp. Model Temperature of Catalytic Reactor ( o C) Temperature of Catalytic Reactor ( o C) T Therm = 35 o C Urea: ppm, HNCO: 216 ppm, NH 3 : 284 ppm T Therm = 15 o C Urea: 143 ppm, HNCO: 17 ppm, NH 3 : 17 ppm Ind. Eng. Chem. Res.,45 (26) 526.

39 Monolith reactor fabrication CuZSM5 powder Washcoated honeycomb reactor Metal (Cu) content 2.9 wt.% Porosity a.71 Si/Al 14 Washcoats thickness 27 μm Ion exchange level 97 % Catalyst weight a 19.7 wt. % BET surface area 337 m 2 /g CPSI 2 a Washcoats (CuZSM5 + alumina binder, without cordierite) SEM image

40 Monolith Reactor Model l Mole balance of the gas phase reactants in channel b dci b s b b, u = km, i Ae ( Ci Ci ) at x = C i = Ci dx l Mole balance over the catalyst layer of thickness dy 2 d Ci De i = r at y = =, 2 i dy s at y = R C i = C i l Mole balance at axial position x of the honeycomb reactor over the external gas film dc i dy dc dy b s i k m, i ( Ci Ci ) = De, i ( ) s Sh = B( d L Pe).45 = kmd D h Assumption Steady state Isothermal conditions No axial dispersion of mass in the channel Fully developed laminar velocity profile in the channel Identical conditions within each monolith channel Ind. Eng. Chem. Res.,45 (26) 526.

41 Model Prediction (NH 3 /SCR over Monolith reactor) Effect of Reactor SV [Gas composition: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance Catalyst: monolith reactor washcoated by CuZSM5; SV: 5, ~ 15, h -1 ] Ind. Eng. Chem. Res.,45 (26) 526.

42 Model Prediction (Urea/SCR over Monolith reactor) Effect of Thermal Decomposition Reactor Temperature [Gas composition: 5 ppm NO, 5 ppm NH 3, 5 % O 2, 1 % H 2 O and N 2 balance Catalyst: monolith reactor washcoated by CuZSM5; SV: 1, h -1 ] Feed to SCR reactor at T Therm = 35 o C : 56 ppm Urea, 189 ppm HNCO, 199 ppm NH 3 Feed to SCR reactor at T Therm = 15 o C : 191 ppm Urea, 59 ppm HNCO, 59 ppm NH 3 Ind. Eng. Chem. Res.,45 (26) 526.

43 Transient Model (NH 3 /SCR over CuZSM5 catalyst) l l l Governing equation for the gas species Coverage of component k The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. w: molar flow rate (mol/s) A tot : front area of the monolith (m 2 ) x g. : mole fraction of gas species x s : mole fraction of gas species at surface k m : mass-transfer coeff. (mol/m 2 /s) S: geometric surface area per reactor volume (m -1 ) a: active density (mol-site/m 3 ) s: stoichiometric coeff. r: reaction rate (mol/mol-site/s) Reactions rate expressions for NH 3 adsorption/desorption, NH 3 oxidation and NO oxidation l NH 3 adsorption/desorption NH 3 oxidation NO oxidation Reactions rate expressions for Standard SCR, Fast SCR, NO 2 SCR and N 2 O formation The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Standard SCR Fast SCR NO 2 SCR N 2 O formation Olsson et al., Appl. Catal. B: Environ., 81 (28) 23.

44 Model Prediction (NH 3 /SCR over CuZSM5 catalyst) Variation: Temperature Variation: NH 3 concentration Feed: 5 ppm NO, 5 ppm NH 3, 8 % O 2, 5 % H 2 O and Ar balance Reactor SV: 18,4 h -1 ; Flow rate: 3,5cc/min Feed: 25 ppm NO, 25 ppm NO 2, 2~8 ppm NH 3, 8 % O 2, 5 % H 2 O and Ar balance Reactor SV: 18,4 h -1 ; Flow rate: 3,5cc/min Reaction Temperature: 175 o C The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Olsson et al., Appl. Catal. B: Environ., 81 (28) 23.

45 Transient Model (other catalysts) Fe/Zeolite catalyst 1. Eley-Rideal model: site 1 (surface acidic site) Ind. Eng. Chem. Res., 5 (211) 285. Predicting the conversion of NOx and NH 3 with respect to NO 2 /NOx feed ratio. 2. Dual site model: site 1 (surface acidic site), site 2 (for the physisorbed NH 3 and NH 4 NO 3 ) Sjövall et al., Ind. Eng. Chem. Res. 49 (21) 39. Describing a variety of transient behaviors as a function of reaction temperature and concen tration of feed gas compositions. V 2 O 5 -WO 3 /TiO 2 catalyst Redox kinetic model: site 1 (vanadyl species), site 2 (surface acidic site) Nova et al., AIChE J., 55 (29) 1515, Tronconi et al., Ind. Eng. Chem. Res., 49 (21) Unifying the Standard and Fast SCR reaction by redox mechanism Describing the inhibition of denox performance by NH 3, which could be hardly predicted b y the previous model (Eley-Rideal based) Modeling the transient behavior with respect to the feed gas composition including NOx and NH 3.

46 Summary l Urea/SCR technology is one of the most promising technologies to meet the ever-tig htening worldwide environmental regulations including EURO V and SULEV for r educing NO emissions from diesel engine. l CuZSM5, FeZSM5 and V 2 O 5 /TiO 2 catalysts have been recognized as a commercial catalyst for the Urea/SCR technology and the eco-friendly Mn-based catalyst devel oped and the CuSSZ13 catalyst recently reported may overcome the drawback of t he conventional catalysts. l The deactivation of Urea/SCR catalyst including hydrothermal stability and Sulfur and HC tolerances should be resolved to directly apply to diesel after-treatment sys tem. l The reaction kinetics developed well predict the reactor performance of urea deco mposition, NH 3 /SCR as well as Urea/SCR over the wide range of experimental cond itions. l A variety of transient kinetic models well describes the dynamic behavior over CuZ SM5, Fe/Zeolite and V 2 O 5 -WO 3 /TiO 2 catalysts with respect to temperature, concent ration of feed gas compositions, etc.

47 Prospective Issues for urea/scr technology l Modification of the urea decomposition process to lower the urea deco mposition temperature for guaranteeing the low-temperature activity o f SCR catalysts. l Combination of SCR technology with LNT or TWC catalytic system in cluding passive NH 3 /SCR technology to remove NOx emitted from lean -burn engine. l Application of Urea/SCR system to next-generation engine employing alternative fuel including biodiesel and diesel with alcohol, similar to E -85 for gasoline. l Development of deactivation kinetic model for predicting the change of denox performance with respect to catalyst mileage. Urea/SCR system for next-generation vehicle with high fuel efficiency under ever-tightening emission regulations

48 Acknowledgment General Motors Hyundai-Kia Motors The National Research Fo undation of Korea (NRF)