Composition-driven Cu-speciation and reducibility in Cu-CHA zeolite catalysts: a multivariate XAS/FTIR approach to complexity

Martini, Andrea; Borfecchia, Elisa; Lomachenko, Kirill A.; Панкин, И. А.; Negri, Chiara; Berlier, Gloria; Beato, Pablo; Falsig, Hanne; Bordiga, Silvia; Lamberti, Carlo

doi:10.1039/c7sc02266b

Cited by 175 publications

(218 citation statements)

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“…Unless Cu is present at levels exceeding the ion-exchange capacities of the particular SSZ-13 composition used, the current general consensus is that, in the freshly prepared specimens, Cu is present as isolated ions, including Cu 2+ balanced by two nearby framework negative charges (abbreviated as Cu 2+ -2Z, where Z represents a charged zeolite framework site) and a [Cu(OH)] + species balanced by one framework negative charge (as [Cu(OH)] + -Z) [17,[31][32][33]. It is also generally agreed, based on almost identical X-ray absorption near edge structure (XANES) spectra with model Cu salt solutions, that these ions are fully solvated as [Cu(H 2 O) 6 ] 2+ and [Cu(OH)(H 2 O) 5 ] + complexes in hydrated ambient samples [20,34,35]. These two ions are, for practical purposes, spectroscopically indistinguishable and they reside in the Chabazite (CHA) cages where they have relatively small (i.e., longer range) interactions with the CHA framework.…”

Section: Transformations Of Cu Active Speciesmentioning

confidence: 96%

“…With the removal of H 2 O ligands, Cu ions now migrate to cationic exchange positions and bond to lattice O (O L ) of the zeolite framework. Such a change is well reflected by changes in unit cell parameters of the CHA substrate from X-ray diffraction (XRD) [27,35], -OH and H 2 O vibrations from FTIR [35], X-ray absorption and emission spectra (XAS and XES) [20] and hyperfine interactions between the unpaired electron and the nuclear spin of Cu(II) (I = 3/2) from electron paramagnetic resonance (EPR) [36]. It is now well-documented that in dehydrated Cu/SSZ-13, Cu 2+ -2Z with Cu ions located in windows of 6-membered rings (6 MR) are the energetically most favorable configuration.…”

Section: Dehydrationmentioning

confidence: 99%

“…In particular, a number of studies discovered that [Cu(OH)] + -Z can populate before Cu 2+ -2Z saturation [18,20,37] [20], even though all of the Cu ions can, in principle, be more thermodynamically stabilized as Cu 2+ -2Z ( Figure 2). 5 ] + ions are likely spectroscopically indistinguishable by XANES, indirect evidence does exist for the reversible reaction described in Reaction (1) from electron paramagnetic resonance (EPR) measurements.…”

Section: Dehydrationmentioning

confidence: 99%

“…Applying multivariate curve resolution (MCR) techniques to XANES linear combination fit (LCF) analysis, Martini et al [20] recently studied dehydration of a series of Cu/SSZ-13 materials with varying compositions. Using 5 model structures, detailed Cu transformations as a function of temperature were quantified and the results are shown in Figure 4.…”

Section: Dehydrationmentioning

confidence: 99%

“…Now after 3 years, new and exciting results have appeared in literature, especially with respect to the developing molecular-level understanding of the nature of the active Cu species under realistic operating (i.e., situ/operando) conditions, as well as the SCR reaction mechanisms [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. As such, it seems timely to review these new fundamental understandings.…”

Section: Introductionmentioning

confidence: 99%

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Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

Gao

Peden

2018

Catalysts

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Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry.

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Section: Transformations Of Cu Active Speciesmentioning

confidence: 96%

Section: Dehydrationmentioning

confidence: 99%

Section: Dehydrationmentioning

confidence: 99%

Section: Dehydrationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

Gao

Peden

2018

Catalysts

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New Strategies for the Preparation of Sinter‐Resistant Metal‐Nanoparticle‐Based Catalysts

et al. 2019

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The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201901905. Supported metal nanoparticles are widely used as catalysts in the industrial production of chemicals, but still suffer from deactivation because of metal leaching and sintering at high temperature. In recent years, serious efforts have been devoted to developing new strategies for stabilizing metal nanoparticles. Recent developments for preparing sinter-resistant metalnanoparticle catalysts via strong metal-support interactions, encapsulation with oxide or carbon layers and within mesoporous materials, and fixation in zeolite crystals, are briefly summarized. Furthermore, the current challenges and future perspectives for the preparation of highly efficient and extraordinarily stable metal-nanoparticle-based catalysts, and suggestions regarding the mechanisms involved in sinter resistance, are proposed. Nanoparticle Catalysts

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Single‐Atom Catalysts Supported by Crystalline Porous Materials: Views from the Inside

et al. 2020

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Reducing the size of nanoparticle catalysts is one desirable method that can improve their catalytic activity. Single-atom catalysts (SACs) represent the smallest possible size a catalyst can achieve with maximum atomic efficiency. [6] Moreover, recent studies have shown that the use of single-atom catalytic sites, rather than ensembles of atoms, is crucial in many catalytic reactions. [7] Without proper protection, however, single-atom sites in these catalysts are not stable since they tend to aggregate and form larger particles. [8-10] To solve this problem, many different protecting supports have been developed such as polymers and porous organic cages. [11,12] Crystalline porous materials, such as zeolites and metal-organic frameworks (MOFs), have been widely used to stabilize small metal species in catalytic reactions due to the controllable size, shape, and dimensions of their pores and channels. [13-15] Therefore, they are highly desirable in supporting SACs. [13] Despite the promising aspects of zeolite and MOF-supported SACs, their characterization remains challenging due to the single-atomic nature of their bonding environments; atomic-level resolution is needed for the structural characterization of these catalysts. X-ray absorption spectroscopy (XAS) is a powerful tool in studying the structure and properties of atoms in their coordination environments with subatomic resolution, [16,17] and thus is considered particularly suitable for the study of SACs. [16,17] In this contribution, a comprehensive review of representative works on zeolite-and MOF-protected SACs will be presented from the XAS perspective. The subatomic resolution (0.01 Å level) of synchrotron-based XAS technique allows for views from "inside" the SACs regarding their structure, electronic properties, and catalytic activities. The processed data from extended X-ray absorption fine structure (EXAFS) will be shown as a powerful tool to probe the atomic structure of SACs in zeolites and MOFs. Through the standard fitting analysis of EXAFS, together with the assistance of advanced analysis tools, detailed information concerning the local structure of SACs can be obtained. Additionally, it will be demonstrated that the X-ray absorption near-edge structure (XANES) can provide insight into the unique electronic properties of SACs. Furthermore, in situ/operando XAS techniques, coupled with state-of-the-art Single-atom catalysts (SACs) have recently emerged as an exciting system in heterogeneous catalysis showing outstanding performance in many catalytic reactions. Single-atom catalytic sites alone are not stable and thus require stabilization from substrates. Crystalline porous materials such as zeolites and metal-organic frameworks (MOFs) are excellent substrates for SACs, offering high stability with the potential to further enhance their performance due to synergistic effects. This review features recent work on the structure, electronic, and catalytic properties of zeolite and MOF-protected SACs, offering atomic-scale views from the "insid...

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Composition-driven Cu-speciation and reducibility in Cu-CHA zeolite catalysts: a multivariate XAS/FTIR approach to complexity

Abstract: Multivariate XAS analysis and in situ FTIR enable an unprecedented quantitative understanding of the composition impact on temperature-dependent Cu-speciation and reducibility in Cu-CHA zeolite catalysts.

Cited by 175 publications

References 87 publications

Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

New Strategies for the Preparation of Sinter‐Resistant Metal‐Nanoparticle‐Based Catalysts

Single‐Atom Catalysts Supported by Crystalline Porous Materials: Views from the Inside

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