Adsorption and co-adsorption of NO and water on LaCu-ZSM5

• Competitive adsorption of NO and H2O on LaCu-ZSM-5 was investigated at 50–125 °C.
• H2O displaces irreversibly Cu mono-nitrosyl ad-species.
• Bridged and chelating nitrates on copper sites are not affected by water and are thermally more stable.
• H2O can be removed at lower temperature compared to nitrates.

The effect of water on NO adsorption on LaCu-ZSM5 has been studied by in-situ FTIR at 50 °C identifying for which copper sites NO adsorption competes with water. The relative thermal stability of NO and H2O ad-species have been also determined by increasing the sample temperature from 50 to 400 °C. Water was removed from zeolite at temperature lower than that necessary to desorb NO, as both bridged and chelating nitrates, from copper sites.A quantitative analysis of the adsorption of NO on the zeolite previously contacted with water was made by carrying out adsorption tests at temperatures far from those activating any DeNOx reaction in a lab-scale PFR reactor. The variation of the amount of adsorbed NO with the temperature of H2O desorption has been evaluated increasing the desorption temperature from 125 to 500 °C after zeolite saturation with water at 125 °C. The total recovery of the amount of NO adsorbed on the dry zeolite demonstrated the reversibility of water deactivation.

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