Surface chemistry of H-ZSM5 studied by time-resolved IR spectroscopy

Jentys, Andreas; Warecka, Gerhard; Lercher, Johannes A.

doi:10.1016/0304-5102(89)80010-0

Cited by 49 publications

(30 citation statements)

References 26 publications

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“…The band at 1458 cm )1 can be assigned to NH 4 + since peaks in this area are reported to be generated by ammonium ions arising from the protonation of ammonia on Brønsted acid sites, and the band around 1620 cm )1 has been assigned to Lewis bound ammonia by the same authors [19,23,[33][34][35][36]. Another possible assignment of the band around 1620 cm )1 is water [36][37][38][39]. It is probable that some water was present during the adsorption of ammonia and the band at 1620 cm )1 may thus be a combination of bands due to both ammonia and water.…”

Section: No X Adsorptionmentioning

confidence: 99%

Identification of adsorbed species on Cu-ZSM-5 under NH3 SCR conditions

et al. 2007

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The selective catalytic reduction of nitrogen oxides with ammonia as the reducing agent was studied using Fourier transform infrared (FTIR) spectroscopy. The adsorbed species found on a Cu-ZSM-5 powder during exposure to NO, NO 2 or NH 3 was compared to the adsorbed species identified during SCR conditions. A blocking effect caused by ammonia at 175°C was investigated by a stepwise increase of the ammonia concentration, and the spectra indicated that the formation of nitrites or nitrates decreased as surface coverage of ammonia increased. No such effect was observed at 350°C, since the oxidation of ammonia results in very low ammonia coverage. The effect of changes in the NO to NO 2 ratio was also studied at 350°C, and the species identified during SCR reaction indicated that the enhanced activity at equimolecular amounts of NO and NO 2 possibly involves gas phase components as well as adsorbed species.

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Section: No X Adsorptionmentioning

confidence: 99%

Identification of adsorbed species on Cu-ZSM-5 under NH3 SCR conditions

et al. 2007

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“…2), it corresponds to the hydrogen bonding of NH 3 , as claimed previously [26]. A great deal of this band might represent mutual hydrogen bonding between already adsorbed NH 3 molecules [22].…”

Section: Resultsmentioning

confidence: 76%

“…Other authors also claimed Brùnsted character of bands at 3200±3400 cm ±1 [22]. Since all NH 4 + should decompose during the treatment up to 400 C under vacuum [25], in our particular case bands at 3200±3400 cm ±1 , 2800±3000 cm ±1 and 1458 cm ±1 should probably be attributed to the remaining water species which from the walls of the chamber are slowly building up and adsorb on Brùnsted sites of the samples.…”

Section: Resultsmentioning

confidence: 92%

“…However, the terminal SiOH at 3741 cm ±1 are the consequence of template decomposition, and those OH ± groups do not serve as Brùnsted sites since they are located inside the channels [19]. In addition, there is a band at 1630 cm ±1 , which was previously assigned to Lewis sites [22], and to both Lewis and Brùnsted sites [23].…”

Section: Resultsmentioning

confidence: 96%

“…As for the part of NH 3 chemically adsorbed, it is impossible to say which fraction is related to which particular acid sites. Some previous investigations showed a very small concentration of Lewis-bound ammonia molecules on HZSM-5 with Si/Al = 36 [22]. Similarly, calorimetric investigation of ZSM-5 with Al/Si = 33 also showed that the majority of acidity comes from Brùnsted acid sites, but two kinds of Lewis sites of different strength were present as well [28].…”

Section: Resultsmentioning

confidence: 97%

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Acid Sites in HZSM-5 Upon Copper Exchange by FTIR and DSC Using Ammonia

Bošković¹,

Vulic

Kis

et al. 2001

Chem. Eng. Technol.

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The acidity of the parent HZSM‐5 zeolite and Cu‐HZSM‐5 catalyst has been examined by FTIR and DSC using ammonia desorption. Sites of different strength were found in HZSM‐5, desorbing ammonia at a relative temperature difference of about 100 °C. Upon copper exchange a fraction of Brønsted sites were transformed to Lewis sites, but the acid strength of the remaining Brønsted sites was increased. Aside from Lewis sites originating from copper exchange, there might be some additional sites formed from precipitated copper. This could explain the quantity of adsorbed NH3 on Cu‐ZSM‐5 which is higher than theoretically expected. While changing their nature, acid sites of higher strength keep their location, which is manifested by some diffusion effect towards ammonia.

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Infrared Spectroscopy for the Characterization of Surface Acidity and Basicity

Knözinger

2008

Handbook of Heterogeneous Catalysis

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Surface chemistry of H-ZSM5 studied by time-resolved IR spectroscopy

Cited by 49 publications

References 26 publications

Identification of adsorbed species on Cu-ZSM-5 under NH3 SCR conditions

Identification of adsorbed species on Cu-ZSM-5 under NH3 SCR conditions

Acid Sites in HZSM-5 Upon Copper Exchange by FTIR and DSC Using Ammonia

Infrared Spectroscopy for the Characterization of Surface Acidity and Basicity

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