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Title: Mechanistic insight into the passive NOx adsorption in the highly dispersed Pd/HBEA zeolite

Abstract

Passive NOx adsorption using zeolite supported Pd catalysts has been considered one of most effective methods for low-temperature NO storage in diesel engine emission control. In the present work, first-principles density functional theory calculations were used to study NO adsorption at the highly dispersed Pd sites, i.e., monomeric PdIIO and dimeric [PdIIOPdII]2+ in the H-BEA zeolite. It has been found that each PdIIO and [PdIIOPdII]2+ sites could bind with three and four NO molecules, respectively. Upon adsorption, NO could be oxidized to NO2, resulting in the reduction of PdII to Pd0 for PdIIO and PdII to PdI, for [PdIIOPdII]2+, respectively. With increasing NO coverage at both sites, NO oxidation becomes more facile with low activation barriers of 13 and 22 kJ/mol. At the PdIIOPdII site, the binding of formed NO2 becomes weak at high NO coverage. Both PdIIO and [PdIIOPdII]2+ sites are protonated to the more stable [PdIIOH]+ and [PdIIOH]+/[PdIIOH]+ sites in the presence of H2O or neighboring BAS sites. Finally, we studied the CO effect on the NO adsorption in Pd/H-BEA. With co-fed CO in the NOx mixture, both PdIIO and [PdIIOPdII]2+ could be reduced to Pd0 and [PdI-PdI]2+ sites. Compared to the NO adsorption, our calculations show thatmore » CO adsorption is slightly stronger at the [PdIIOPdII]2+ site while it is slightly weaker at the PdIIO site. CO oxidation, rather than NO oxidation readily occurs if NO and CO co-adsorbed. The reduced PdI site and the [PdIIOH]+/[PdIIOH]+ site enhances NO adsorption.« less

Authors:
ORCiD logo; ORCiD logo; ORCiD logo;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1492709
Report Number(s):
PNNL-SA-137552
Journal ID: ISSN 0926-860X
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Applied Catalysis. A, General
Additional Journal Information:
Journal Volume: 569; Journal Issue: C; Journal ID: ISSN 0926-860X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
passive NOx adsorption, density functional theory, HBEA zeolite, Pd

Citation Formats

Mei, Donghai, Gao, Feng, Szanyi, Janos, and Wang, Yong. Mechanistic insight into the passive NOx adsorption in the highly dispersed Pd/HBEA zeolite. United States: N. p., 2019. Web. doi:10.1016/j.apcata.2018.10.037.
Mei, Donghai, Gao, Feng, Szanyi, Janos, & Wang, Yong. Mechanistic insight into the passive NOx adsorption in the highly dispersed Pd/HBEA zeolite. United States. doi:10.1016/j.apcata.2018.10.037.
Mei, Donghai, Gao, Feng, Szanyi, Janos, and Wang, Yong. Tue . "Mechanistic insight into the passive NOx adsorption in the highly dispersed Pd/HBEA zeolite". United States. doi:10.1016/j.apcata.2018.10.037.
@article{osti_1492709,
title = {Mechanistic insight into the passive NOx adsorption in the highly dispersed Pd/HBEA zeolite},
author = {Mei, Donghai and Gao, Feng and Szanyi, Janos and Wang, Yong},
abstractNote = {Passive NOx adsorption using zeolite supported Pd catalysts has been considered one of most effective methods for low-temperature NO storage in diesel engine emission control. In the present work, first-principles density functional theory calculations were used to study NO adsorption at the highly dispersed Pd sites, i.e., monomeric PdIIO and dimeric [PdIIOPdII]2+ in the H-BEA zeolite. It has been found that each PdIIO and [PdIIOPdII]2+ sites could bind with three and four NO molecules, respectively. Upon adsorption, NO could be oxidized to NO2, resulting in the reduction of PdII to Pd0 for PdIIO and PdII to PdI, for [PdIIOPdII]2+, respectively. With increasing NO coverage at both sites, NO oxidation becomes more facile with low activation barriers of 13 and 22 kJ/mol. At the PdIIOPdII site, the binding of formed NO2 becomes weak at high NO coverage. Both PdIIO and [PdIIOPdII]2+ sites are protonated to the more stable [PdIIOH]+ and [PdIIOH]+/[PdIIOH]+ sites in the presence of H2O or neighboring BAS sites. Finally, we studied the CO effect on the NO adsorption in Pd/H-BEA. With co-fed CO in the NOx mixture, both PdIIO and [PdIIOPdII]2+ could be reduced to Pd0 and [PdI-PdI]2+ sites. Compared to the NO adsorption, our calculations show that CO adsorption is slightly stronger at the [PdIIOPdII]2+ site while it is slightly weaker at the PdIIO site. CO oxidation, rather than NO oxidation readily occurs if NO and CO co-adsorbed. The reduced PdI site and the [PdIIOH]+/[PdIIOH]+ site enhances NO adsorption.},
doi = {10.1016/j.apcata.2018.10.037},
journal = {Applied Catalysis. A, General},
issn = {0926-860X},
number = C,
volume = 569,
place = {United States},
year = {2019},
month = {1}
}