☆ 4.8 Article

Investigation of the active sites and optimum Pd/Al of Pd/ZSM-5 passive NO adsorbers for the cold-start application: Evidence of isolated-Pd species obtained after a high-temperature thermal treatment

APPLIED CATALYSIS B-ENVIRONMENTAL (2018)

Journal

APPLIED CATALYSIS B-ENVIRONMENTAL

Volume 226, Issue -, Pages 71-82

Publisher

ELSEVIER SCIENCE BV

DOI: 10.1016/j.apcatb.2017.12.031

Keywords

Low temperature; Pd/ZSM-5; NO adsorption site; Si-to-Al molar ratio

Funding

National Research Foundation of Korea(NRF) grant - Korea government(MSIP) [NRF-2016R1A5A1009592]
Ministry of Science, ICT, and Future Planning (MSIP)
Pohang University of Science and Technology (POSTECH)

Ask authors/readers for more resources

Protocol

Community support

Reagent

Community support

Abstract

We investigated the chemisorptive NO adsorption ability at a low temperature (120 degrees C) of the Pd/ZSM-5 passive NOx adsorbers (PNA) to address the cold-start NOx emission. The Pd/ZSM-5 showed a much higher NO adsorption ability after the oxidative treatment at 750 degrees C compared with the 500 degrees C treatment; according to the combined EXAFS, XPS and XRD results, atomically dispersed Pd species were formed over the former, while small PdO agglomerates were observed over the latter. The Pd species on the Pd/ZSM-5 were further examined by applying a NH4NO3-titration method, where an ion exchange occurred with only the ionic Pd in the zeolite. When the Pd(2)/ZSM-5 was treated at 750 degrees C, it exchanged ions with an NH4NO3 solution whereby most of the Pd was ion-exchanged, and this resulted in a decreased NO adsorption capability. Alternatively, a much lesser amount of ion-exchanged Pd was found on the Pd/ZSM-5 that was treated at 500 degrees C. The combined results indicate that the ionic-Pd species on the ZSM-5, not the bulk PdO, are the active sites for the chemisorptive NO adsorption at the low temperature. The NO adsorption capability was also investigated as a function of the Pd loading and the Si-to-Al-2 molar ratio of the ZSM-5. The results suggest that an optimum Pd-to-Al molar ratio exists for the Pd/ZSM-5 with the maximum NO adsorption capability, which was found at around 0.25, thereby suggesting that the Al in the ZSM-5 framework led to the high dispersion of the ionic-Pd species up to the optimum Pd/Al ratio. Above the optimum Pd/Al ratio, however, the bulk-PdO phase formed on the ZSM-5 resulting in a lower NO adsorption capability; that is, the ZSM-5 with the higher Al content required a higher Pd amount for the attainment of the optimum NO adsorption capability. In summary, the chemisorptive NO adsorption at the low temperature is significantly influenced by both the Si-to-Al-2 molar ratio and the Pd-to-Al molar ratio of the Pd/ZSM-5 catalysts.

Authors

I am an author on this paper

Click your name to claim this paper and add it to your profile.

Reviews

Primary Rating

4.8

Not enough ratings

Secondary Ratings

Novelty

Significance

Scientific rigor

Rate this paper

Iodine capture by ZSM-5 with different Si/Al ratios: An experimental and molecular simulation investigation

Qian-Fan Li, Rui-Li Yu, Zhen-Le Li, Liang-Zhi Xia

Summary: In this paper, the performance and mechanism of iodine capture by ZSM-5 molecular sieves from nuclear power waste gas were analyzed by experiments and molecular simulations. The experiment results showed that the iodine adsorption capacity increased with the increasing Si/Al ratio of the ZSM-5 and varied with temperature. After four adsorption-desorption cycles, it maintained good morphology and adsorption performance. The molecular simulation results revealed that the increased Si/Al ratio led to an increase in iodine adsorption capacity, which was consistent with the experimental findings. This study further enhances our understanding of the capture process and adsorption mechanism of iodine and provides a favorable scheme for treating nuclear waste gas.

MICROPOROUS AND MESOPOROUS MATERIALS (2023)