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Elucidating N2O Formation during the Cyclic NOx Storage and Reduction Process Using CO as a Reductant
Jun Wang, Xiuting Wang, Jinxin Zhu
1‡Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, People's Republic of China.
Environmental Science & Technology
|May 30, 2015
Summary
This study reveals nitrous oxide (N2O) formation during NOx storage and reduction (NSR) with CO. Water addition generally decreases N2O, but can increase it at low temperatures in specific phases.
Area of Science:
- Catalysis
- Environmental Chemistry
- Automotive Emissions Control
Background:
- Nitrous oxide (N2O) is a potent greenhouse gas, and its formation during NOx storage and reduction (NSR) processes is a significant environmental concern.
- Understanding the N2O formation pathways is crucial for developing cleaner automotive emission control technologies.
- The role of water (H2O) in influencing N2O production during NSR, particularly with carbon monoxide (CO) as a reductant, requires detailed investigation.
Purpose of the Study:
- To investigate the N2O formation pathways during the NSR process using CO over a Pt-BaO/Al2O3 catalyst.
- To elucidate the effect of H2O on N2O formation across different phases of the NSR cycle.
- To understand the underlying mechanisms of N2O generation and mitigation strategies.
Main Methods:
- NSR activity measurements were conducted to assess catalyst performance and N2O evolution.
- Transient in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was employed to probe surface species and reaction mechanisms.
- Experiments were performed under varying conditions to analyze N2O formation in lean, rich, and delay phases.
Main Results:
- N2O is formed in all three phases: lean, rich, and delay.
- In the lean phase, N2O formation is linked to isocyanate reactions with NO; H2O addition reduces N2O by hydrolyzing isocyanates.
- In the rich phase, H2O decreases N2O at higher temperatures due to enhanced reduction by H2 from the water-gas shift reaction; in the delay phase, H2O can increase N2O at low temperatures by destabilizing nitrites.
Conclusions:
- The N2O formation mechanism is phase-dependent during CO-based NSR.
- Water plays a complex role, generally inhibiting N2O but potentially promoting it under specific low-temperature delay phase conditions.
- These findings provide critical insights for optimizing NSR catalysts to minimize N2O emissions.
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