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Keturakis, Christopher
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Ammonium Nitrate Formation and Decomposition on an Extruded Vanadium-Based SCR Catalyst

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Christopher Keturakis, Z. Gerald Liu
  • Technical Paper
  • 2020-01-1320
To be published on 2020-04-14 by SAE International in United States
In this study, the formation and decomposition of ammonium nitrate (AN) on a state-of-the-art extruded vanadium-based SCR catalyst (V-SCR) under simulated exhaust conditions has been evaluated. Results show that AN readily forms and accumulates at temperatures below 200°C when exposed to NH3 and NO2. The rate of AN accumulation increases with decreasing temperature. A new low temperature NH3 release peak (not present following NH3 storage conditions with NH3 only) becomes apparent after AN accumulation at 100 and 125°C. This new NH3 release, with a peak release temperature of approximately 180°C, is evaluated in detail to better determine its origin. BET surface area, and thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC), and reactor-based experiments are all used to characterize AN formed on the V-SCR catalyst in comparison to pure AN. Experiments on pure AN crystals reveal that the new low temperature NH3 peak is attributable to the release of NH3 from AN that is not related to AN volatilization, since this does not occur until above T > 200°C.This study expands the present understanding of AN formation…
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A Case Study of a Cu-SSZ-13 SCR Catalyst Poisoned by Real-World High Sulfur Diesel Fuel

Cummins Emission Solutions-Yuanzhou Xi, Nathan Ottinger, Christopher Keturakis, Z. Gerald Liu
  • Technical Paper
  • 2020-01-1319
To be published on 2020-04-14 by SAE International in United States
To meet increasingly stringent diesel engine emission regulations, diesel engines are required to use ultra-low sulfur diesel (ULSD) and are equipped with advanced aftertreatment systems. Cu-SSZ-13 zeolite catalysts are widely used as selective catalytic reduction (SCR) catalysts due to their high NOx reduction and excellent hydrothermal stability. However, active Cu sites of Cu-SSZ-13 catalysts can be poisoned by exposure to engine exhaust sulfur species. This poison effect can be mitigated with the use of ULSD and high temperature exposure from engine operation. On the other hand, ULSD is still not universally available where regulations require it, and vehicles may inadvertently operate with high sulfur diesel fuel (HSD) in some locations. The high concentration of exhaust sulfur species resulting from HSD combustion may rapidly poison the Cu-SSZ-13 SCR catalyst. In this study, the catalytic performance of a sulfur poisoned Cu-SSZ-13 SCR catalyst is analyzed. Results show that the as received SCR catalyst displays substantially low NOx conversion below 350 °C. A thermal treatment at 550 °C can recover most of its lost performance. Temperature programmed desorption…
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Low-Temperature NH3 Storage, Isothermal Desorption, Reactive Consumption, and Thermal Release from Cu-SSZ-13 and V2O5-WO3/TiO2 Selective Catalytic Reduction Catalysts

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Christopher Keturakis, Z. Gerald Liu
Published 2019-04-02 by SAE International in United States
Worldwide, regulations continue to drive reductions in brake-specific emissions of nitric oxide (NO) and nitrogen dioxide (NO2) from on-highway and nonroad diesel engines. NOx, formed as a byproduct of the combustion of fossil fuels (e.g., natural gas, gasoline, diesel, etc.), can be converted to dinitrogen (N2) through ammonia (NH3) selective catalytic reduction (SCR). In this study, we closely examine the low-temperature storage, isothermal desorption, reactive consumption, and thermal release of NH3 on commercial Cu-SSZ-13 and V2O5-WO3/TiO2 SCR catalysts. Catalyst core-reactor, N2 adsorption (BET) surface area, and in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) experiments are utilized to investigate the fundamental chemical processes relevant to low-temperature (T < 250°C) NH3 SCR. Results show that NH3 stored at low-temperature continuously, yet slowly releases from the SCR catalysts, and that nearly all of the weakly bound NH3 stored on Cu2+ sites of the Cu-SSZ-13 catalyst will isothermally desorb from the catalyst in the absence of NOx. However, in the presence of NOx, a large fraction of this weakly bound NH3 will react with NOx, contributing to the…
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Impact of Hydrothermal Aging on the Formation and Decomposition of Ammonium Nitrate on a Cu/zeolite SCR Catalyst

SAE International Journal of Engines

Cummins Emission Solutions-Nathan Ottinger, Yuanzhou Xi, Christopher Keturakis, Z. Gerald Liu
  • Journal Article
  • 2017-01-0946
Published 2017-03-28 by SAE International in United States
Low-temperature (T ≤ 200°C) NOx conversion is receiving increasing research attention due to continued potential reductions in regulated NOx emissions from diesel engines. At these temperatures, ammonium salts (e.g., ammonium nitrate, ammonium (bi)sulfate, etc.) can form as a result of interactions between NH3 and NOx or SOx, respectively. The formation of these salts can reduce the availability of NH3 for NOx conversion, block active catalyst sites, and result in the formation of N2O, a regulated Greenhouse Gas (GHG). In this study, we investigate the effect of hydrothermal aging on the formation and decomposition of ammonium nitrate on a state-of-the-art Cu/zeolite selective catalytic reduction (SCR) catalyst. Reactor-based constant-temperature ammonium nitrate formation, temperature programmed oxidation (TPO), and NO titration experiments are used to characterize the effect of hydrothermal aging from 600 to 950°C. N2 adsorption (BET) surface area and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) experiments are also conducted in order to correlate the morphological effects of hydrothermal aging with concomitant changes in ammonium nitrate chemistry. The insights provided herein support the diesel aftertreatment communities’ ongoing…
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