Title: Effects of Treatment Conditions on Pd Speciation in CHA and Beta Zeolites for Passive NO _x Adsorption

Abstract

The structure and evolution of Pd species in Pd-exchanged zeolite materials intended for use as passive NOx adsorbers were examined under various pretreatment conditions. Using in situ CO-diffuse reflectance infrared spectroscopy, Pd structures were characterized after 500 °C pretreatments in inert (Ar), water (1-2% H2O in Ar), oxidizing (air), and reducing (H2, CO) atmospheres. Two zeolites of similar Si/Al ratios but different framework topologies (Beta, CHA) were found to show different distributions of Pd species, depending on the reducing agent used. Reduction in H2 (500 °C; 10% H2 in Ar) followed by re-oxidation (500 °C; air) led to higher amounts of single-site Pd ions on Pd-CHA than Pd-Beta, whereas high-temperature reduction in CO (500 °C; 1000 ppm CO in Ar) followed by re-oxidation (500 °C; air) led to significant loss of ionic Pd on both Pd-CHA and Pd-Beta, albeit H2 temperature-programmed reduction and XPS experiments suggest that these phenomena may be limited to surface Pd. High-temperature treatments with water (500 °C; 1-2% H2O in Ar) are shown to form either Pd metal or PdO particles, with Pd-Beta being more susceptible to these effects than Pd-CHA. This work suggests that the effects of CO are especially problematic with respect to themore » durability of these materials in passive NOx adsorption applications, especially in the case of Beta zeolite.« less

Authors:

Pace, Robert B. ^[1]; Lardinois, Trevor M. ^[2]; Ji, Yaying ^[3]; Gounder, Rajamani  ^[2];

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Heintz, Olivier ^[4]; Crocker, Mark  ^[1]

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+ Show Author Affiliations

1. Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, Kentucky 0511, United States, Department of Chemistry, University of Kentucky, 161 Jacobs Science Building, Lexington, Kentucky 40506, United States
2. Charles D. Davidson School of Chemical Engineering, Purdue University, 701 W Stadium Ave. #3000, West Lafayette, Indiana 47907, United States
3. Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, Kentucky 0511, United States
4. Laboratoire Interdisciplinaire Carnot de Bourgogne (LICB), UMR CNRS 6303, Université de BourgogneFranche-Comté, 9 Avenue Alain Savary, 21078 Dijon Cedex, France

Publication Date:

2021-10-25

Research Org.:

Univ. of Kentucky, Lexington, KY (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1827231

Alternate Identifier(s):

OSTI ID: 1829669; OSTI ID: 1845149

Grant/Contract Number:  

EE0008213

Resource Type:

Published Article

Journal Name:

ACS Omega

Additional Journal Information:

Journal Name: ACS Omega Journal Volume: 6 Journal Issue: 44; Journal ID: ISSN 2470-1343

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Palladium; Pretreatment; Atmospheric chemistry; Zeolites; Materials; Passive NOx adsorber, Palladium, Zeolite, DRIFTS, XPS