On kinetic modeling of change in active sites upon hydrothermal aging of Cu-SSZ-13

Daya, Rohil; Joshi, Saurabh Y.; Luo, Jinyong; Dadi, Rama Krishna; Currier, Neal W.; Yezerets, Aleksey

doi:10.1016/j.apcatb.2019.118368

Cited by 49 publications

(27 citation statements)

References 23 publications

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“…Two Cu species are recognized to be present in the Cu-CHA catalyst: Z 2 Cu II (doubly coordinated to the framework) and ZCu II OH (balanced by one framework negative charge), whose relative ratio can be predicted based on Si/Al and Cu/Al ratios [5,6,11]. The proportion of such Cu species could also be affected by several factors, for example, hydrothermal aging [4,6,12] or hydrated/dehydrated conditions [5,6]. It was also proposed, based on DFT calculations, DRIFTS, XAS and NH 3 -TPD tests [4,5,8,13], that these two species are able to coordinate a different number of NH 3 molecules, thus influencing, in turn, the NH 3 storage capacity, a relevant parameter for the SCR process.…”

Section: Introductionmentioning

confidence: 99%

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The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration

et al. 2021

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The present work is focused on the effect of water on NH3 adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO2/Al2O3) ratios and Cu loadings were studied under both dry and wet conditions. H2O adversely affects NH3 adsorption on Lewis acid sites (Cu ions) over all the tested catalysts, as indicated by the decreased NH3 desorption at low temperature during TPD. Interestingly, the NH3/Cu ratio, herein regarded as an index for the speciation of Cu cations, fell in the range of 3–4 (in the presence of gaseous NH3) or 1–2 (no gaseous NH3) in dry conditions, in line with the formation of different NH3-solvated Cu species (e.g., [CuII(NH3)4]2+ and [CuII(OH)(NH3)3]+ with gaseous NH3, [Z2CuII(NH3)2]2+ and [ZCuII(OH)(NH3)]+ without gaseous NH3). When H2O was fed to the system, on the contrary, the NH3/Cu ratio was always close to 3 (or 1), while the Brønsted acidity was slightly increased. These results are consistent both with competition between H2O and NH3 for adsorption on Lewis sites and with the hydrolysis of a fraction of Z2CuII species into ZCuIIOH.

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Section: Introductionmentioning

confidence: 99%

“…NH 3 can also be adsorbed on the Brønsted acid sites typical of the zeolite framework, according to the adsorption chemistry reported below [12]:…”

Section: Introductionmentioning

confidence: 99%

The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration

et al. 2021

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“…The mechanism of the SCR reaction over Cu zeolites is disputed in the literature, and different reaction pathways have been proposed. No single unified mechanism exists, and it appears that the SCR mechanism changes with zeolite structure, Cu loading, and temperature region [32,[38][39][40]. For Cu-SSZ-13, spectroscopic evidence suggests the formation of a Cu(NH 4 ) 2 complex at a low temperature (<300 • C) that is active for NO x reduction.…”

Section: Scr Catalysts For Scrofmentioning

confidence: 99%

“…The reoxidation of Cu + to Cu 2+ by O 2 does not show such linear correlation, and Cu + -O 2 -Cu + dimers and other oligomers have been suggested. This implies the migration to Cu atoms between the zeolite cage and the continuous dispersion/aggregation of the active sites [32,[38][39][40].…”

Section: Scr Catalysts For Scrofmentioning

confidence: 99%

Aftertreatment Technologies for Diesel Engines: An Overview of the Combined Systems

2021

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The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NOx and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an after-treatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NOx under lean-burn operation conditions are selective catalytic reduction (SCR) and the lean NOx trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NOx and soot abatement strategies. The main focus of this review is on combined technologies for NOx removal (i.e., LNT–SCR) and for the simultaneous removal of NOx and soot, like SCR-on-Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems.

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“…Recently, the same group were able to link the HA kinetics of the active sites to a transient kinetic model of NH 3 adsorption and desorption of fresh Cu-CHA in order to simulate the NH 3 -TPD profiles of the aged catalysts. This was based on the mean-field approximation, implying constant turnover Arrhenius rate constants for the adsorption and desorption reactions, but with changing individual site densities directly affecting the rates associated with the aforementioned reactions [58]. However, it has also been shown that via H 2 -TPR, NH 3 -TPD, DRIFTS [29,30,50] and in situ time-resolved XAS [26] that the NH 3 -TPD profiles of Cu-CHA are much more complicated than proposed in [56].…”

Section: Introductionmentioning

confidence: 99%

An Aging Model of NH3 Storage Sites for Predicting Kinetics of NH3 Adsorption, Desorption and Oxidation over Hydrothermally Aged Cu-Chabazite

et al. 2020

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A unified transient kinetic model which can predict the adsorption, desorption and oxidation kinetics of NH3 over hydrothermally aged Cu-chabazite was developed. The model takes into account the variation of fractional coverages of NH3 storage sites due to hydrothermal aging. In order to determine the fractional coverage of these sites, the catalyst was aged for various times at a certain temperature followed by NH3 adsorption, desorption and temperature-programmed desorption (TPD) experiments. TPD profiles were deconvoluted mainly into three peaks with centres at 317, 456 and 526 °C, respectively. Hydrothermal aging resulted in the progressive increase in the intensity of the peak at 317 °C and decrease in the intensity of the peaks at 456 and 526 °C, along with decreased NH3 oxidation at high temperatures. A model for hydrothermal aging kinetics of the fractional coverage of storage sites was developed using three reactions with appropriate rate expressions with parameters regressed from experimental data. The model was then incorporated into a multi-site kinetic model for the degreened Cu-Chabazite by the addition of aging reactions on each storage site. The effects of both aging time and temperature on the kinetics NH3 adsorption, desorption and oxidation were successfully predicted in the 155-540 °C range. This study is the first step towards the development of a hydrothermal aging-unified kinetic model of NH3-Selective Catalytic Reduction over Cu-chabazite.

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On kinetic modeling of change in active sites upon hydrothermal aging of Cu-SSZ-13

Cited by 49 publications

References 23 publications

The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration

The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration

Aftertreatment Technologies for Diesel Engines: An Overview of the Combined Systems

An Aging Model of NH3 Storage Sites for Predicting Kinetics of NH3 Adsorption, Desorption and Oxidation over Hydrothermally Aged Cu-Chabazite

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