Analysis of NH 3 ‐TPD Profiles for CuSSZ‐13 SCR Catalyst of Controlled Al Distribution – Complexity Resolved by First Principles Thermodynamics of NH 3 Desorption, IR and EPR Insight into Cu Speciation**
| Autor: | Piotr Pietrzyk, Edyta Tabor, Kinga Mlekodaj, Kinga Góra-Marek, Bartosz Mozgawa, Zbigniew Sojka, Monika Fedyna, Zhen Zhao, Filip Zasada, Jiří Dědeček |
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| Rok vydání: | 2021 |
| Předmět: | |
| Zdroj: | Chemistry – A European Journal. 27:17159-17180 |
| ISSN: | 1521-3765 0947-6539 |
| Popis: | NH3 temperature-programmed desorption (NH3 -TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx . Herein, we propose an interpretation of NH3 -TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+ , Cu+ , [CuOH]+ centers, dimeric [Cu-O-Cu]2+ , [Cu-O22- -Cu]2 species, segregated CuO nanocrystals and Bronsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3 -TPD experiment. Thus, a rigorous interpretation of the NH3 -TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. |
| Databáze: | OpenAIRE |
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