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Performance and Mechanistic Aspects of Ag/MgO/\({\varvec{\gamma}}\)-Al2O3 as a Passive NOx Adsorber

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Abstract

The potential of Ag/MgO/\(\gamma \)-Al2O3 (Ag/Mg–Al) as a passive NOx adsorber is evaluated, and is found to be superior as compared to Ag/\(\gamma \)-Al2O3. Two different adsorption sites exist on both Ag/Mg–Al and Ag/\(\gamma \)-Al2O3, and it is inferred that the primary role of MgO is not to provide additional adsorption sites but to decrease the Ag particle size, which results in a higher activity towards NOx adsorption. The product distribution profile with either NO or NO2 in the feed is found to be nearly the same at early times, which indicates the formation of the same surface species with either of the reactants. It is deduced that the facile conversion of nitrites to nitrates occurs in the presence of H2, but the extent of conversion decreases at longer times. A sequential configuration of the in-house Ag/Mg–Al and a commercial Cu/SSZ-13 catalyst yielded a NOx reduction efficiency of 85% at low temperatures as against 7% with the standalone Cu/SSZ-13 catalyst.

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Abbreviations

\(m\) :

Mass of the catalyst (g)

\({\overline{\text{N}}}_{{{\text{NO}}_{x} }}\) :

Moles of NOx adsorbed per unit mass of catalyst (mol/g)

\(\left[ {{\text{NO}}_{x} } \right]_{in}\) :

NOx concentration at the inlet of catalyst bed (mol/m3)

\(\left[ {{\text{NO}}_{x} } \right]_{out}\) :

NOx concentration at the outlet of catalyst bed (mol/m3)

\(\dot{\vartheta }\) :

Total volumetric flow rate (m3/s)

\({\text{X}}_{{{\text{NO}}_{x} }}\) :

Steady-state NOx conversion (%)

\(t\) :

Time (s)

\(\eta\) :

Cumulative NOx adsorption and reduction efficiency (%)

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Acknowledgements

We would like to thank Sasol Germany GmbH for providing the doped alumina samples used in this work. One of the authors (Prateek Khatri) would like to acknowledge Pranav V. Kherdekar and Marvi Kaushik (Department of Chemical Engineering, IIT Delhi) for the technical discussions. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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  1. Department of Chemical Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India

    Prateek Khatri & Divesh Bhatia

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  1. Prateek Khatri
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Correspondence to Divesh Bhatia.

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Khatri, P., Bhatia, D. Performance and Mechanistic Aspects of Ag/MgO/\({\varvec{\gamma}}\)-Al2O3 as a Passive NOx Adsorber. Catal Lett 151, 3298–3312 (2021). https://doi.org/10.1007/s10562-021-03565-0

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