Pd-Doped SSZ-13 for Low-T NOx Adsorption: an Operando FT-IR Spectroscopy Study

• Published in: Topics in catalysis Vol. 66; no. 13-14; pp. 750 - 760
• Main Authors: Hamid, Y., Matarrese, R., Morandi, S., Castoldi, L., Lietti, L.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-08-2023; Springer Nature B.V
• Subjects: Acetates; Adsorption; Carbonyls; Catalysis; Catalysts; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Decomposition; Dehydration; Desorption; Fourier transforms; High temperature; Industrial Chemistry/Chemical Engineering; Infrared spectroscopy; Low temperature; Microreactors; Nitrates; Nitrosyls; Original Paper; Pharmacy; Physical Chemistry; Propylene; Spectrum analysis; Thermal stability; NOx adsorbers; SSZ-13; Pd-doped zeolites; PNA; Pd; Cold-start
• ISSN: 1022-5528; 1572-9028
• DOI: 10.1007/s11244-022-01737-9

In this study, mechanistic aspects of NO adsorption/desorption over a home-made Pd/SSZ-13 passive NOx adsorber (PNA) catalyst are investigated. Operando FT-IR spectroscopy and microreactor experiments are performed to envisage the performance of the catalyst and the pathway involved in NO adsorption, with particular emphasis to the impact of species such as C
3
H
6
and CO. In the absence of C
3
H
6
and CO, NO is observed to adsorb as nitrosyls (anhydrous and hydrated) over both Pd
2+
and Pd
+
species, and as nitrates. 80 μmolNO
x
/g
cat
(NO/Pd molar ratio of 0.8) are adsorbed. The stability of nitrosyls is higher in comparison to the nitrates in that the former initially dehydrate and further decompose at elevated temperatures (> 300 °C) leading to the evolution of NO. The presence of CO and C
3
H
6
negatively affects the amounts of NO adsorbed (53 and 45 μmolNO
x
/g
cat
, respectively) due to the reduction of Pd sites. CO admission to the catalyst forms a variety of carbonyl species over Pd
2+
, Pd
+
and Pd
0
sites which upon NO admission are readily displaced and NO is adsorbed as hydrated/anhydrous nitrosyls of Pd
n+
. The nitrosyls so formed exhibit lower thermal stability in comparison to nitrosyls observed in the absence of CO and decompose below 300 °C. The addition of C
3
H
6
leads to the apparent formation of oxidized species like acetone, acrolein and acetates, besides propylene adsorption. The NO adsorption in the presence of C
3
H
6
leads to the formation of Pd
n+
(NO)(X) complexes; upon heating the decomposition of this complexes is observed at low temperatures along with propylene and water desorption. Formation of organic nitro-compounds is also observed that decompose at higher temperatures.