Accelerated Aging of Fe-Zeolite SCR Catalysts: Engine and Bench-Flow Approaches Prof. Ke Nguyen Mechanical, Aerospace and Biomedical Engineering University of Tennessee at Knoxville, USA Presented at HCM City University of Technology May 27, 2008

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 2 Acknowledgements Research is supported by the U.S. Department of Energy (DOE), Office of FreedomCAR and Vehicle Technologies, Fuels Technology Program. Fe-Zeolite SCR catalysts used were provided by Catalytic Solutions

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 3 Outline  Engine-based aging and performance evaluation  Bench flow reactor-based performance evaluation of fresh and engine-aged Fe-Zeolite SCR catalysts  Results of surface characterization studies of fresh and engine-aged Fe-Zeolite SCR catalysts

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 4 High-Temperature Thermal Aging of Fe-Zeolite SCR Catalysts  Key concern for Fe-Zeolite SCR catalysts durability  High temperatures periodically required to regenerate DPFs  Expected deactivation mechanisms  Lube-oil poisoning  Contaminations from DOC  Changes in zeolite structure  Washcoat breakdown, i.e., crackings

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 5 Background of SCR Catalysts  Metal oxide SCR catalysts: V 2 O 5 supported on either TiO 2 or Al 2 O 3 - High NOx reduction ( ~90%) - Low temperature ( °C) - Lack of high-temperature durability - Emitting volatile vanadyl species - High catalyzing potential to oxidize SO 2 to SO 3 SO 3 reacts with NH 3 to form ammonium sulfate and bisulfate: catalyst poisoning  Zeolite SCR catalysts: most common Cu and Fe-Zeolite - High NOx reduction (~90%) over large temperature range( °C) - High temperature heavy-duty diesel applications - Low potential to oxidize SO 2 to SO 3 - Cu-Zeolite produces more N 2 O than Fe-Zeolite  Focus only on Fe-Zeolite SCR catalysts

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 6 SCR Reactions Between NH 3 and NO x  Major reactions in the SCR process : 4NH 3 + 4NO + O 2 4N 2 + 6H 2 0(1) 4NH 3 + 2NO + 2NO 2 4N 2 + 6H 2 0 (2) 4NH 3 + 3NO 2 3.5N 2 + 6H 2 0 (3)  Reaction 2 is the fastest reaction  Reaction 1 is the intermediate reaction  Reaction 3 is the slowest reaction

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 7 SCR of NO x by NH 3  Alpha (α) is defined as the ratio of NH 3 to NOx  Exhaust gases consist mainly of NO (~90%), an α of 1 is required to reduce NO x (reaction 1)  In most systems some NO is oxidized to NO 2 with a DOC to increase the ratio NO 2 :NO in exhaust gases  SCR generally proceeds according to reaction 2  NO 2 /NO must not be greater than 1, since reaction 3 is slowest  NH 3 can be solely introduced to the exhaust gases without prior oxidation of NO to NO 2

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 8 Engine-Based Aging

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 9 Schematic of Engine Aftertreatment Fe-Zeolite SCR catalysts evaluated as system with DOC and DPF T1Inlet Air T2Oil Sump T3Exhaust Manifold T4DOC Inlet gas T5DOC Exit gas T6SCR Inlet gas T7SCR Exit/DPF Inlet gas T8DPF Exit gas T9DPF Internal P1Oil Pressure P2Exhaust Pressure

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 10 Specifications of Aftertreatment System DOCMixerSCRDPF DOC Inlet gas DOC Exit gas SCR Inlet gas SCR Exit Gas DPF T1 DPF Exit gas Cat In Cat Out

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 11 Engine Bench Setup Located at NTRC SCR Catalysts Syringe Pump Drive Motor 500cc Hatz Engine Throttle Controller Exhaust Sampling Exhaust Fuel Injection

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 12 Engine-Based Aging and Evaluation  Engine operates steady state at 1500 rpm  ~800 ppm NO x, exhaust temperature ~350°C, GHSV = h -1  SCR catalysts are aged by raising exhaust gas temperature during active DPF regeneration  Supplemental fuel is injected into the exhaust upstream of the DOC  Aging cycles  Up to 50 aging cycles of 25 minutes each  Atomized fuel is injected in five-minute increments until exhaust temperatures of 600, 750 and 850°C are achieved then cut off fuel  Desired exhaust temperatures are obtained at fuel cut-off  Evaluation cycles  Evaluation is carried out after a given number of aging cycles at an exhaust temperature of ~350°C  Inject 5% of NH 3 in N 2 mixture such that α = NH 3 /NO = 0.6 to minimize NH 3 slip

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 13 SCR Catalysts Used in Engine Bench Fe-Zeolite SCR catalysts of 400 cpsi and cordierite substrate mainly used for heavy-duty diesel applications are provided by Catalytic Solutions 7.6 cm 15.2 cm

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 14 SEM Micrographs of Fresh Fe-Zeolite SCR Catalyst Channels shown are uniform Washcoat thickness varies

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 15 Energy Dispersive Spectroscopy (EDS) of Fresh Fe-Zeolite SCR Catalyst EDS performed on washcoat corner of few atomic layer Al, Si, O, Fe, Ce, Zr and Au peaks detected Al, Si, O and Fe are components of zeolite Ce and Zr are components of oxygen storage materials Au peak is from gold coating applied to the sample before performing SEM

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 16 Typical temperature profiles during SCR catalyst aging on engine bench at 650°C(α = 0.6) Repeatable temperature profile during aging Axial temperature variation in SCR catalyst SCR catalyst inlet experiences higher temperature than exit (~90°C)

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 17 NO x emissions during SCR catalyst aging on engine bench at 650 ° C (α = 0.6) Cycle to cycle variation of NO x emissions during aging Half of NO is oxidized to NO 2 by DOC and DPF During engine evaluation less than half of NOx out is NO NO x conversion of ~50% is obtained with α = 0.6 Cat In NO and NO x (no NH 3 ) Cat Out NO x (with NH 3 ) Cat Out NO (no NH 3 ) Cat Out NO (with NH 3 )

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 18 Typical temperature profiles during SCR catalyst aging on engine bench at 750°C (α = 0.6) Temperature profile is repeatable Axial temperature variation in SCR catalyst Front section of SCR catalyst experiences higher temperature than rear section (~100°C)

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 19 NO x emissions during SCR catalyst aging on the engine bench at 750 ° C Cycle to cycle variation of NO x emissions during aging NO x conversion evaluated with α = 0.6 Cat In NO and NO x (no NH 3 ) Cat Out NO x (with NH 3 ) Cat Out NO (no NH 3 ) Cat Out NO (with NH 3 )

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 20 Typical temperature profiles during SCR catalyst aging on engine bench at 850ºC (α = 0.6) Repeatable temperature profile Axial temperature variation along SCR catalyst Smaller temperature difference between SCR inlet and exit (~ 40°C)

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 21 NO x emissions during SCR catalyst aging on engine bench at 850°C Cycle to cycle variation of NO x emissions during aging NO x conversion evaluated with α = 0.6 Cat Out NO (no NH 3 ) Cat In NO and NO x (no NH 3 ) Cat Out NO (with NH 3 ) Cat Out NO x (with NH 3 )

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 22 Bench-Flow Reactor Performance Evaluation

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 23  Bench reactor evaluation of fresh and engine-aged Fe-Zeolite SCR catalysts  Temperature varied between 200 and 600°C  α varied between 0.5 and 1.2  Surface characterization studies  SEM-EDS, EPMA, XRD and BET Bench-Flow Reactor Evaluation

24 Performance Evaluation of Fresh and Engine-Aged SCR Catalysts is Carried Out on Bench-Flow Reactor SCR Catalyst Reactor

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 25 Fe-Zeolite SCR Catalysts - Fresh Fe-Zeolite SCR catalysts - Engine-aged Fe-Zeolite catalysts Two cored samples are obtained from engine-aged catalysts: front half and rear half Evaluation is performed separately on both engine-age samples 22 mm75 mm

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 26 Thermocouple locations in SCR catalyst 5mm 19mm 38mm 57mm Flow 75.5mm

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 27 Composition of Simulated Exhaust Gases Gas SpeciesConcentration H 2 O (g)5% O2O2 14% CO 2 5% NO 350ppm NH ppm N2N2 balance NOx performance evaluations are performed at GHSV of 30,000 h -1

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 28 Typical SCR catalyst temperature at different locations during evaluation at 500ºC, GHSV = 30,000 h -1 Steady state temperatures obtained during evaluation ∆T max =19°C

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 29 NOx conversion of fresh Fe-Zeolite SCR catalysts with 350 ppm NO at GHSV of 30,000 h -1 Maximum NO x conversion of 94% occurs at 400ºC at α = 1.2 NOx conversion increases with α Lower NO x conversion at T>500°C due to oxidation of NH 3 Low NO x conversion at 200°C due to kinetics

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 30 NO x Conversion of Engine-Aged Fe-Zeolite SCR Catalysts (α=1) Front section of both engine-aged catalysts degraded severely Reduction in NOx performance in front-half is possibly due to lube-oil poisoning, contaminations from DOC and cracking of washcoat Catalyst aged at 650°C is being evaluated

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 31 XRD patterns of fresh and aged Fe-Zeolite SCR Catalysts Significantly less zeolite detected in aged samples Fe 2 O 3 and Al 2 O 3 peaks are discernable in aged samples Zeolite structure begins to breakdown around 800°C for many high-silica zeolites ∆ - Ce x Zr 1-x O 2 ◊ - ZrO 2 □ - Zeolite ○ - CeO 2 ● - Cordierite † - Fe 2 O 3 ♠ - Al 2 O 3 ♦ - Si □ ● □ ∆ ● ○ ∆ ∆ ∆ ◊ ∆ † † † † † † † ♠ ♠ † ♦ † ♠ 64 hrs on BFR (28ppm SO 2 ) 13 cycles at 850°C (Front) 13 cycles at 850°C (Rear) Fresh Fe-SCR

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 32 Expanded XRD patterns of fresh and engine-aged Fe-Zeolite SCR catalysts Zeolite Fresh °C

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 33 BET surface area measurements of fresh and engine-aged Fe-Zeolite SCR catalysts Surface area includes zeolite and cordierite substrate Front sections of engine-aged SCR catalysts experience severe loss of surface area Surface area is higher if cordierite substrate is excluded Surface area reduction correlates with aging temperature

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 34 EPMA elemental maps of fresh Fe-Zeolite SCR catalyst Fe is well-dispersed in washcoat ZrO 2 and CeO 2 are the oxygen storage materials Si is one of constituent of zeolite Trace of P is detected ZnP SCaFe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 35 EPMA elemental maps of Fe-SCR catalyst aged for 31 cycles at 650°C (front) Fe is still well dispersed in washcoat Agglomeration of ZrO 2 and CeO 2 More P is detected in front due to lube-oil contamination Trace of Pt is detected Pt P S CaFe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 36 EPMA elemental maps of Fe-Zeolite SCR catalyst engine-aged for 31 cycles at 650°C (rear) Fe is well-dispersed in washcoat Trace of Pt is detected Agglomeration of ZrO 2 and CeO 2 Less P deposited in rear section Pt P S CaFe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 37 EPMA elemental maps of Fe-Zeolite SCR catalyst engine-aged for 50 cycles at 750°C (front) Cracking of washcoat is visible in front section due to higher temperature Contamination from lube oil, i.e., P Pt P S Ca Fe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 38 EPMA elemental maps of Fe-Zeolite SCR catalyst engine- aged for 50 cycles at 750°C (rear) Temperature in rear-half is much less than 750C No cracking of washcoat is observed in rear- half, which explains higher NOx conversion Only trace of Pt is detected Pt P S Ca Fe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 39 EPMA elemental maps of Fe-ZeoliteSCR catalyst engine-aged for 13 cycles at 850°C (front) Severe crackings of washcoat Zn P S Ca Fe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 40 EPMA elemental maps of Fe-SCR engine-aged for 13 cycles at 850°C (rear) Severe cracking of washcoat Zn P S Ca Fe SiZrCe

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 41 Conclusions  Loss of NO x performance of engine- aged Fe-Zeolite SCR catalysts is mainly due to: - Loss of surface area (BET) - Breakdown of zeolite structure at temperatures above 800°C (XRD) -Severe cracking of washcoat at temperatures above 750°C (EPMA) -Agglomeration of CeO 2 and ZrO 2 -Contamination from lube-oil

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 42 Thank You Questions ????