Characterization of Cu-SSZ-13 NH3 SCR catalysts: an in situ FTIR study

• Published in: Physical chemistry chemical physics : PCCP Vol. 15; no. 7; pp. 2368 - 2380
• Main Authors: SZANYI, Janos, KWAK, Ja Hun, HAIYANG ZHU, PEDEN, Charles H. F
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 21.02.2013
• Subjects: Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Ion-exchange; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties; In situ; Transition metal; Zeolite; Characterization; Infrared spectrometry; Gas solid adsorption; Ammonia; Heterogeneous catalysis; Nitric oxide; Carbon monoxide; Copper; Catalyst; Modified material
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp43467a

The adsorption of CO and NO over Cu-SSZ-13 zeolite catalysts, highly active in the selective catalytic reduction of NO(x) with NH(3), was investigated by FTIR spectroscopy, and the results obtained were compared to those collected from other Cu-ion exchanged zeolites (Y,FAU and ZSM-5). Under low CO pressures and at room temperature (295 K), CO forms monocarbonyls exclusively on the Cu(+) ions, while in the presence of gas phase CO dicarbonyls on Cu(+) and adsorbed CO on Cu(2+) centers form, as well. At low (cryogenic) sample temperatures, tricarbonyl formation on Cu(+) sites was also observed. The adsorption of NO produces IR bands that can be assigned to nitrosyls bound to both Cu(+) and Cu(2+) centers, and NO(+) species located in charge compensating cationic positions of the chabasite framework. On the reduced Cu-SSZ-13 samples the formation of N(2)O was also detected. The assignment of the adsorbed NO(x) species was aided by adsorption experiments with isotopically labeled (15)NO. The movement of Cu ions from the sterically hindered six member ring position to the more accessible cavity positions as a result of their interaction with adsorbates (NO and H(2)O) was clearly evidenced. Comparisons of the spectroscopy data obtained in the static transmission IR system to those collected in the flow-through diffuse reflectance cell points out that care must be taken when general conclusions are drawn about the adsorptive and reactive properties of metal cation centers based on a set of data collected under well defined, specific experimental conditions.