Active and spectator adsorbates during NO decomposition over Cu--ZSM-5: Transient IR, site-poisoning, and site-promotion studies
A site-poisoning and -promotion technique was employed to investigate the role of adsorbates and to formulate a reaction pathway for the NO decomposition reaction over Cu-ZSM-5. Transient infrared and mass spectrometer studies of pulse NO reaction on under- and over-exchanged Cu-ZSM-5 reveal Cu{sub 2+}(NO), Cu{sub +}(NO), bridging Cu{sub 2+}(NO{sub 3}{sup {minus}}), and NO{sup +} as the major adsorbates and N{sub 2}, N{sub 2}O, O{sub 2}, and NO{sub 2} as the products. SiH{sub 4} and H{sub 2}O moderately inhibited Cu{sup +}(NO) and N{sub 2} formation, but severely inhibited Cu{sup 2+}(NO{sub 3}{sup {minus}}) and O{sub 2} formation. Addition of CO as a reducing agent led to the promotion of Cu{sup 2+} reduction to Cu{sup +}, depletion of Cu{sup 2+}(NO{sub 3}{sup {minus}}), increase in NO conversion and O{sub 2} formation as well as formation of CO{sub 2}. These results revealed that N{sub 2} and O{sub 2} formation proceeds through separate rate-limiting steps; O{sub 2} formation occurs via both auto reduction of Cu{sup 2+} to Cu{sup +} and decomposition of Cu{sup 2+}(NO{sub 3}{sup {minus}}). The results from pulse reaction studies on deactivated Cu-ZSM-5 reveal that O{sub 2} formation is more sensitive to poisoning than NO dissociation and N{sub 2} formation. Although silanation may improve the hydrothermal stability of the catalyst, silanation severely inhibited O{sub 2} and Cu{sup 2+}(NO{sub 3}{sup {minus}}) formation through inhibition of adsorbed O migration. Promotion of O{sub 2} desorption by addition of a small amount of reducing agent such as CO in the presence of No (NO/CO {gt} 3.5) can greatly enhance NO decomposition activity. Further investigation is needed to study such an effect on the NO decomposition activity under the O{sub 2} environment.
- Research Organization:
- Univ. of Akron, OH (US)
- OSTI ID:
- 20003843
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 187; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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