Effect of gas composition on the NOx adsorption and reduction activity of a dual-function Ag/MgO/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"><mml:mi>γ</mml:mi></mml:math>-Al2O3 catalyst

Khatri, Prateek; Bhatia, Divesh

doi:10.1016/j.apcata.2021.118114

Cited by 13 publications

(1 citation statement)

References 38 publications

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“…Passive NO x adsorbers (PNAs) have been proposed to address the cold-start NO x emissions by trapping NO x at low temperatures (<200 °C) and releasing it at a higher temperature (>250 °C) where the downstream NO x reduction catalysts such as LNT or SCR are active . Various materials have been synthesized and evaluated for their NO x adsorption and desorption characteristics. − Among the different materials studied, Pd supported on zeolites, especially Pd/Chabazite (Pd/CHA), has been found to be the most suitable. , …”

Section: Introductionmentioning

confidence: 99%

Effect of H₂O and CO on the NO Operating Cycle in Pd/CHA Passive NO_x Adsorbers

Kaushik,

Khan,

Haider

et al. 2024

J. Phys. Chem. C

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DFT simulations are performed to understand the impact of H 2 O and CO on the NO interaction with Pd sites present at various locations in Pd/CHA passive NO x adsorbers. The presence of H 2 O facilitates the reduction of [PdOH−PdOH] +2 and [Pd−O−Pd] +2 by NO in 8-membered rings (8MR) but increases the activation barrier in 6MR. Bidentate nitrates are formed in the absence of H 2 O, whereas monodentate nitrates are formed in the presence of H 2 O, which transform to bidentate nitrates upon H 2 O desorption. The detrimental effect of H 2 O on NO binding over [PdOH−PdOH] +2 and [PdOH] + is mitigated in the presence of CO. Additionally, CO preferentially reduces the Pd(II) species when both CO and NO are coadsorbed on [Pd−O−Pd] +2 , resulting in the formation of Pd +1 for further NO uptake. H 2 O does not significantly impact the reduction of Pd(II) species by CO.Pd +1 sites can also reoxidize to Pd(II) species under an oxidizing atmosphere. However, the reoxidation of Pd +1 is inhibited in the presence of H 2 O in 6MR and 8MR, which could explain the reported increase in the NO x desorption temperature. The operating cycle of NO, including the transformation of Pd species and the effect of H 2 O and CO on NO x uptake and release, is proposed.

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Section: Introductionmentioning

confidence: 99%

Effect of H₂O and CO on the NO Operating Cycle in Pd/CHA Passive NO_x Adsorbers

Kaushik,

Khan,

Haider

et al. 2024

J. Phys. Chem. C

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Effect of H₂, H₂O, and CO₂ on the deNO_x characteristics of a combined passive NO_x adsorber and NO_x reduction catalyst

Khatri

Bhatia

2022

AIChE Journal

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The effect of H2, H2O, and CO2 on the NOx removal characteristics of a non‐PGM material (Ag/MgO/γ‐Al2O3) is investigated, which is shown to be active for both NOx adsorption and reduction. H2O facilitates NOx adsorption at early times but inhibits it at longer times. The inhibiting effect of CO2 is observed at low temperatures and is proposed to be due to bicarbonates. However, the inhibiting effect of both H2O and CO2 decreases at higher temperatures. The formation of NO2 at low temperatures is attributed to NO oxidation, and the contribution of stored NOx to NO2 formation increases with temperature. H2O inhibits NH3 oxidation at high temperatures as well as NOx reduction by NH3‐SCR at low temperatures. However, the NOx reduction activity is not affected by CO2. H2 significantly promotes the NH3‐SCR reactions, which is attributed to the facilitation of NOx spillover from the reduced Ag sites to the support.

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