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- Title
An Assessment of Zeolite Framework Effect for Low-Temperature NO X Adsorbers.
- Authors
Castoldi, Lidia; Morandi, Sara; Ticali, Pierfrancesco; Matarrese, Roberto; Lietti, Luca
- Abstract
Pd-promoted zeolites (Y, ZSM-5, FER, SSZ-13) were prepared and characterized to analyze their properties as low-temperature NOx adsorbers. The samples were investigated by BET and XRD and by in situ FT-IR spectroscopy of CO and NO adsorption to probe the Pd sites and the nature of the adsorbed NOx species. The NOx adsorption/desorption performances at low temperatures were examined by microreactor measurements upon NO/O2 adsorption followed by TPD in the presence of water and carbon dioxide. It was enlightened that: (i) the zeolite framework influences the Pd dispersion: the smaller the zeolite cage, the higher the Pd dispersion, irrespective of the Si/Al ratio. Accordingly, the following Pd dispersion order has been observed, inversely to the zeolite cage size: Pd/SSZ-13 > Pd/ZSM-5 ~ Pd/FER >> Pd/Y; (ii) Pd is present as isolated Pdn+ species and in PdOx particles; (iii) the Pd dispersion governs the NOx storage capacity: the smaller the zeolite cage, the higher the Pd dispersion and the storage capacity; (iv) NO adsorbs mainly in the form of Pd nitrosyls and nitrates; (v) NO desorption occurs both at a temperature below 200 °C and in a high-temperature range (near 350 °C).
- Subjects
NITROSYL compounds; CARBON dioxide in water; ZEOLITES; X-ray diffraction; LOW temperatures
- Publication
Catalysts (2073-4344), 2023, Vol 13, Issue 6, p962
- ISSN
2073-4344
- Publication type
Article
- DOI
10.3390/catal13060962