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Title: A window into selective catalytic reduction : a RAIRS study of NO and NH3 on Cu{311}
Author: Sitathani, Krit
ISNI:       0000 0004 6348 9931
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2017
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This thesis studies the interaction between the bare Cu{311} surface with NO and NH3,individually and co-adsorbed using reflection-absorption infrared spectroscopy (RAIRS). In addition to the bare Cu{311} surface, the interaction of NO and NH3 with the various oxygen phases of the Cu{311} surface phases was also studied. Several other techniques were used in tandem to support the study, such as low energy electron diffraction (LEED) and temperature programmed desorption (TPD) experiments using mass spectrometry. The study was carried out in pursuit an understanding of the underlying mechanism of the selective catalytic reduction (SCR) of NO using NH3 in current diesel engines. The dosing of NO onto the Cu{311} surface at 100 K leads to the initial adsorption of intact NO. After an exposure threshold is reached, individual NO molecules react with another NO molecule to form (NO)2 dimers. These dimer species subsequently form N2O, leaving O(a) on the surface. Oxygen was found to be an inhibitor for the reaction, either due to the reaction in a self-poisoning process or from oxygen pre-dosing onto the Cu{311} surface. Temperature plays a minor role with regards to NO/Cu{311}, as it only affects the amount of NO on the surface along with adsorbate surface mobility. Similarly, NH3 was found to adsorb intact onto the Cu{311} surface and not to react or dissociate at 100 K. Oxygen acts as a site blocker for the adsorption, but can also stabilise NH3 to remain on the surface at higher temperatures due to electronic effects. At 300 K, it was found that both the bare and oxygen pre-covered Cu{311} surface was able to dissociate NH3 into NH2. The co-adsorption of NO and that of NH3 onto the Cu{311} surface were found to be largely independent of each other and the interaction is dominated by the displacement of NO by NH3. However, as NO adsorption on the Cu{311} surface forms O(a), it indirectly affects the adsorption of NH3 by creating an oxygen covered Cu{311} surface, which changes how NH3 adsorbs onto the surface.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Surface Science ; Chemistry ; NO ; NH3 ; Co-adsorption ; Cu ; Copper ; NOx ; NOx Reduction ; Ammonia ; Catalyst ; SCR ; Selective Catalytic Reduction ; IR ; RAIRS ; IRAS ; Reflection-Absorption Infrared Spectroscopy ; Physical Chemistry ; Cu{311} ; Cu(311) ; Single Crystal ; LEED ; TPD ; Temperature Programme Desorption ; UHV ; Ultra High Vacuum