Abstract : Abstract The heavy-duty diesel (HDD) engines use the diesel oxidation catalyst (DOC), catalyzed particulate filter (CPF) and urea injection based selective catalytic reduction (SCR) systems in sequential combination, to meet the US EPA 2010 PM and NOx emission standards. The SCR along with a NH3 slip control catalyst (AMOX) offer NOx reduction >90 % with NH3 slipHowever, there is a strong desire to further improve the NOx reduction performance of such systems, to meet the California Optional Low NOx Standard implemented since 2015. Integrating SCR functionality into a diesel particulate filter (DPF), by coating the SCR catalyst on the DPF, offers potential to reduce the system cost and packaging weight/ volume. It also provides opportunity to increases the SCR volume without affecting the overall packaging, to achieve NOx reduction efficiencies >95 %. xvii In this research, the NOx reduction and NH3 storage performance of a Cu-zeolite SCR and Cu-zeolite SCR catalyst on DPF (SCRF®) were experimentally investigated based on the engine experimental data at steady state conditions. The experimental data for the production-2013-SCR and the SCRF® were collected (with and without PM loading in the SCRF®) on a Cummins ISB 2013 engine, at varying inlet temperatures, space velocities, inlet NOx concentrations and NO2/NOx ratios, to evaluate the NOx reduction, NH3 storage and NH3 slip characteristics of the SCR catalyst. The SCRF® was loaded with 2 and 4 g/L of PM prior to the NOx reduction tests to study the effect of PM loading on the NOx reduction and NH3 storage performance of the SCRF®. The experimental setup and test procedures for evaluation of NOx reduction performance of the SCRF®, with and without PM loading in the SCRF® are described. The 1-D SCR model developed at MTU was calibrated to the engine experimental data obtained from the seven NOx reduction tests conducted with the production-2013-SCR. The performance of the 1-D SCR model was validated by comparing the simulation and experimental data for NO, NO2 and NH3 concentrations at the outlet of the SCR. The NO and NO2 concentrations were calibrated to ±20 ppm and NH3 was calibrated to ±20 ppm. The experimental results for the production-2013-SCR indicate that the NOx reduction of 80 - 85% can be achieved for the inlet temperatures below 250°C and above 450°C and NOx reduction of 90 - 95% can be achieved for the inlet temperatures between 300 - 350°C, at ammonia to NOx ratio (ANR) 1.0, while the NH3 slip out of the SCR wasConversely, the SCRF® showed 90 - 95 % NOx reduction at ANR of 1.0, while the NH3 slip out of the SCRF® was >50 ppm, with and without PM loading in the SCRF®, for the inlet temperature range of 200 - 450°C, space velocity in the range of 13 to 48 k/hr and inlet NO2/NOx in the range of 0.2 to 0.5. The NOx reduction in the SCRF® increases to >98 % at ANR 1.2. However, the NH3 slip out of the SCRF® increases significantly at ANR 1.2. xviii The effect of PM loading at 2 and 4 g/L on the NOx reduction performance of the SCRF® was negligible below 300°C. However, with PM loading in the SCRF®, the NOx reduction decreased by 3 - 5% when compared to the clean SCRF®, for inlet temperature >350°C. Experimental data were also collected by reference [1] to investigate the NO2 assisted PM oxidation in the SCRF® for the inlet temperature range of 260 - 370°C, with and without urea injection and thermal oxidation of PM in the SCRF® for the inlet temperature range of 500 - 600°C, without urea injection by reference [1]. The experimental data obtained from this study and [1] will be used to develop and calibrate the SCR-F model at Michigan Tech. The NH3 storage for the production-2013-SCR and the SCRF® (with and without PM loading) were determined from the steady state engine experimental data. The NH3 storage for the production-2013-SCR and the SCRF® (without PM loading) were within ±5 gmol/m3 of the substrate, with maximum NH3 storage of 75 - 80 gmol/m3 of the substrate, at the SCR/SCRF® inlet temperature of 200°C. The NH3 storage in the SCRF®, with 2 g/L PM loading, decreased by 30%, when compared to the NH3 storage in the SCRF®, without PM loading. The further increase in the PM loading in the SCRF®, from 2 to 4 g/L, had negligible effect on NH3 storage.

Abstract : Selective catalytic reduction (SCR) systems along with a NH3 slip control catalyst (ASC) offers NOx conversion efficiency >90 % with NH3 slip 90 % with NH3 slip 95 %. A downstream SCR catalyst substrate can be used to get additional NOx conversion by using the SCRF® outlet NH3 to increase the cumulative NOx conversion of the system. In this study, NOx reduction, NH3 slip and PM oxidation performance of a Cu-zeolite SCRF® with a downstream Cu-zeolite SCR were investigated based on engine experimental data at steady state conditions. The experimental data were collected at varying SCRF® inlet temperatures, space velocities, inlet NOx concentrations, NO2/ NOx ratios at ammonia to NOx ratios (ANR) between 1.02 to 1.10. The results demonstrated that the SCRF® with downstream SCR together can achieve NOx conversion efficiency > 98% at ANRs between 1.02 - 1.10 (which may have been due to measurement inaccuracies in downstream SCRF 98% at ANRs between 1.02 - 1.10 (which may have been due to measurement inaccuracies in downstream SCRF®/SCRdata), for the inlet temperature range of 200 - 370°C, space velocity in the range of 10 to 34 k/hr and inlet NO2/ NOx in the range of 0.3 - 0.5. However, NH3 slip from the SCRF® decreases and NOx concentration downstream of the SCRF® increases with the oxidation of PM in the SCRF®. The PM oxidation kinetics are affected by the deNOx reactions, hence, the SCRF® with urea dosing showed ~80 % lower reaction rates during passive oxidation when compared to the production CPF. The effect of varying fuel rail injection pressure on the primary particle diameter and on the Elemental Carbon (EC) and Organic Carbon (OC) fraction of the total carbon was also studied. The primary particle diameter was found to be in the range of 28-30 nm with no effect of the variation in fuel rail injection pressure on it. The OC part of the Total Carbon (TC) did not vary significantly with fuel rail injection pressure. The EC content increased with decrease in fuel rail injection pressure.

Selective catalytic reduction (SCR) of NO[Subscript x] with urea/NH[Subscript 3] is a leading candidate to the impending more stringent emissions regulations for diesel engines. Currently, there is no consensus on the durability and the deactivation mechanisms associated with zeolite-based SCR catalysts, nor is there an established protocol for rapidly aging zeolite-based SCR catalysts that replicates the catalyst deactivation associated with field service. A 517 cc single-cylinder, naturally-aspirated direct injection (NA/DI) diesel engine is used to perform accelerated thermal aging on Fe-zeolite SCR catalysts. The engine is fitted with an exhaust aftertreatment system consisting of a DOC, a SCR catalyst and a DPF. Accelerated aging protocol established for the SCR catalyst utilizes high temperature exhaust gases during the active regeneration of the DPF. Accelerated aging is carried out at exhaust gas temperatures of 650, 750 and 850°C at the SCR inlet and at a gas hourly space velocity (GHSV) of approximately 40,000 h−1. The engine is maintained at 1500 rpm and supplemental fuel is injected upstream of the DOC to alter the temperature of the aftertreatment system. The aged Fe-zeolite SCR catalysts are evaluated for NO[Subscript x] performance in a bench-flow reactor and characterized by multiple surface characterization techniques for materials changes. The NO[Subscript x] performance of the front sections of the engine-aged catalysts is severely degraded. BET surface area measurements of the engine-aged catalyst indicate a severe reduction of catalyst surface area in the front sections of the catalysts aged at 750 and 850°C. However, the catalyst aged at 650°C has a catalyst surface area similar to that of a fresh catalyst; thereby ruling out reduction of catalyst surface area as the sole cause of the catalyst deactivation seen in the front sections of the engine-aged catalysts. The similar shape of the NO[Subscript x] conversion profiles observed with these catalyst sections even at different aging temperatures indicates some type of catalyst poisoning; however, the cause of catalyst degradation in these catalyst sections is not identified in this investigation. There is a good relationship between the NO[Subscript x] performance and catalyst aging temperature for the rear sections of the engine-aged catalysts - NO[Subscript x] performance decreases with increasing aging temperature. XRD patterns and NO oxidation experiments reveal evidence of zeolite dealumination in the engine-aged catalysts. BET surface area measurements show that catalyst surface area decreases with increasing aging temperature, which further supports the suggestion of zeolite dealumination as the cause of catalyst deactivation in the rear sections of the engine-aged catalysts. A comparison between the engine-aged and field-aged catalysts is conducted to assess the validity of the implemented accelerated thermal aging protocol in replicating the aging conditions observed in the field-aged catalyst. Bench-flow reactor evaluation is used to determine the NO[Subscript x] performance of the engine-aged and field-aged catalysts, and in depth surface studies are used to determine the deactivation mechanisms associated with each type of catalyst aging. SEM micrographs and BET surface area measurements of the aged catalysts show that the deactivation mechanism associated with catalyst aging is primarily physical damage to the zeolite washcoat for both the field-aged and engine-aged catalysts. Furthermore, X-ray diffraction and NO oxidation experiments identify zeolite dealumination as the underlying cause of the washcoat degradation. Finally, BFR evaluation shows that the NO[Subscript x] performance of the catalyst aged at 750°C for approximately 50 hours compares very well to that of the field-aged catalyst with a service life of 3 years. It is concluded that accelerated thermal aging on the engine bench is successful in bringing about similar catalyst changes to those seen with the field-aged catalyst.

Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts presents a complete overview of the selective catalytic reduction of NOx by ammonia/urea. The book starts with an illustration of the technology in the framework of the current context (legislation, market, system configurations), covers the fundamental aspects of the SCR process (catalysts, chemistry, mechanism, kinetics) and analyzes its application to useful topics such as modeling of full scale monolith catalysts, control aspects, ammonia injections systems and integration with other devices for combined removal of pollutants.

This book is a printed edition of the Special Issue "Selective Catalytic Reduction of NO_x" that was published in Catalysts

The 21st Century Truck Partnership (21CTP), a cooperative research and development partnership formed by four federal agencies with 15 industrial partners, was launched in the year 2000 with high hopes that it would dramatically advance the technologies used in trucks and buses, yielding a cleaner, safer, more efficient generation of vehicles. Review of the 21st Century Truck Partnership critically examines and comments on the overall adequacy and balance of the 21CTP. The book reviews how well the program has accomplished its goals, evaluates progress in the program, and makes recommendations to improve the likelihood of the Partnership meeting its goals. Key recommendations of the book include that the 21CTP should be continued, but the future program should be revised and better balanced. A clearer goal setting strategy should be developed, and the goals should be clearly stated in measurable engineering terms and reviewed periodically so as to be based on the available funds.