A theoretical study on the catalysis of Cu-exchanged zeolite for the decomposition of nitric oxide

Tajima, Nobuo; Hashimoto, Masaya; Toyama, Fuminori; El‐Nahas, Ahmed M.; Hirao, Kimihiko

doi:10.1039/a903383a

Cited by 47 publications

(63 citation statements)

References 44 publications

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“…On the other hand, nitric oxide (NO) is the target of paramount importance in environmental catalysis. After Iwamoto's discovery of an unusually high activity of Cu(I) zeolites in NO decomposition and its revival [1][2][3] there has been an ongoing experimental [4][5][6][7][8][9][10][11][12] and theoretical research [13][14][15][16][17][18][19][20][21][22][23] to understand the details of the mechanism of this process. Despite this tremendous effort, there are still a number of unsettled questions, including fundamental query about the nature of the bonding between various forms of copper and NO molecule.…”

Section: Introductionmentioning

confidence: 99%

On the nature of spin- and orbital-resolved Cu+–NO charge transfer in the gas phase and at Cu(I) sites in zeolites

et al. 2012

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Electronic factors essential for NO activation by Cu(I) sites in zeolites are investigated within spin-resolved analysis of electron transfer channels (natural orbitals for chemical valence). NOCV analysis is performed for three DFT-optimized models of Cu(I)-NO site in ZSM-5: [CuNO] ? , (T1)CuNO, and (M7)CuNO. NO as a non-innocent, openshell ligand reveals significant differences between independent deformation density components for a and b spins. Four distinct components are identified: (i) unpaired electron donation from NO p k * antibonding orbital to Cu s,d ; (ii) backdonation from copper d yz to p \ * antibonding orbital; (iii) donation from occupied p k and Cu d xz to bonding region, and (iv) donation from nitrogen lone-pair to Cu s,d . Channel (i), corresponding to one-electron bond, shows-up solely for spin majority and is effective only in the interaction of NO with naked Cu ? . Channel (ii) dominates for models b and c: it strongly activates NO bond by populating antibonding p* orbital and weakens the N-O bond in contrast to channel (i), depopulating the antibonding orbital and strengthening N-O bond. This picture perfectly agrees with IR experiment: interaction with naked Cu ? imposes small blue-shift of NO stretching frequency while it becomes strongly red-shifted for Cu(I) site in ZSM-5 due to enhanced backdonation.

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Section: Introductionmentioning

confidence: 99%

On the nature of spin- and orbital-resolved Cu+–NO charge transfer in the gas phase and at Cu(I) sites in zeolites

et al. 2012

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“…Many reaction steps possibly involved in the direct NO decomposition on Cu/zeolites have been investigated previously by employing various models and methods. [16][17][18][19][20] Several reaction paths proposed in the literature have been compiled (Scheme 1) along with the reaction energies and activation barriers (where available) reported for the elementary reaction steps. Since these energies were obtained at various levels of theory using different types of models for the active site, a direct comparison should be taken with some caution.…”

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confidence: 99%

“…Another route was proposed following the A!B!C path: [16,17] a simple reaction mechanism based on the readsorption of N 2 O on ZCuO (through the O-end) that leads to the formation of N 2 , O 2 , and ZCu (D!E!F). An activation barrier for the rate-determining step on this path (the formation of ZCuO 2 N 2 ) of 152 and 145 kJ mol À1 has been reported based on BP86/(1-T cluster) [16] and B3LYP/(3-T cluster) [17] calculations, respectively.…”

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confidence: 99%

“…For example, the reaction energies of À107 and À173 kJ mol À1 were reported for reaction step D based on the BP86 functional (using a 1-T cluster model) and based on the B3LYP functional (using a 3-T cluster model), respectively. [16,17] A majority of the proposed reaction mechanisms start with the interaction of two NO molecules with Cu/zeolite (ZCu) producing ZCuO and N 2 O (A!B!C). Different routes were proposed for the subsequent conversion of N 2 O: 1) it can interact with another NO molecule to produce N 2 and NO 2 .…”

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confidence: 99%

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Correlation Between Catalytic Activity and Metal Cation Coordination: NO Decomposition Over Cu/Zeolites

Pulido

Nachtigall

2009

ChemCatChem

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Since Iwamoto's discovery of an unusually high activity of Cu/zeolites in NO decomposition, [1] there has been an ongoing experimental and theoretical quest to understand the details of the mechanism of this process. Despite this tremendous effort, there are still a number of unsettled questions, including the uncertainty about the nature of the reaction intermediates and about the structure of the active site; [2] either the involvement of only a single extra-framework Cu cation [3][4][5][6][7][8] or the concerted effect of two nearby Cu cations, the Cu pair, [9][10][11][12][13][14] was proposed. From the vast amount of relevant experimental data available today, it is clear that the activity of the Cu/zeolite catalysts depends on 1) zeolite topology, 2) zeolite composition (Si/Al ratio and Cu loading), and 3) Cu-exchange procedure, including the sample pretreatment. [4,6,8,12,13,15] However, the understanding of the relationship between active site structure (the metal coordination and localization) and catalytic activity is far from complete; it is our goal to increase our knowledge in this respect.The lack of direct experimental evidence about the transition-state structures and about the details of the reaction mechanism justifies the use of quantum chemistry to provide the missing details. However, a reliable description of the reactions catalyzed by transition metals in a complex environment (such as zeolites) represents a major challenge for contemporary computational chemistry since it requires the use of a model that realistically represents the active site (including its environment) and the use of a method that can consistently describe the electronic structure of the system along the reaction path (see the Methods section). Many reaction steps possibly involved in the direct NO decomposition on Cu/zeolites have been investigated previously by employing various models and methods. [16][17][18][19][20] Several reaction paths proposed in the literature have been compiled (Scheme 1) along with the reaction energies and activation barriers (where available) reported for the elementary reaction steps. Since these energies were obtained at various levels of theory using different types of models for the active site, a direct comparison should be taken with some caution. For example, the reaction energies of À107 and À173 kJ mol À1 were reported for reaction step D based on the BP86 functional (using a 1-T cluster model) and based on the B3LYP functional (using a 3-T cluster model), respectively. [16,17]

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Combining quantum mechanics and interatomic potential functions inab initio studies of extended systems

2000

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The errors made when large chemical systems are replaced by small models are discussed: interrupted charge transfer, missing structure constraints, neglected long‐range interactions. A combined quantum mechanics (QM)–interatomic potential function (Pot) approach is described. Characteristic features of the QM‐Pot approach include: (1) periodic boundary conditions, (2) consistent definition of forces in the presence of link atoms that terminate the QM cluster, (3) interatomic potential functions parametrized on ab initio data and accounting for polarization effects, (4) use of reaction force fields (EVB potentials) in combination with QM methods for efficient localization of transition structures in large systems, (5) implementation as a loose coupling of existing QM and Pot engines. Comparison is made with some other hybrid QM/MM methods. Applications of the combined QM‐Pot method for ab initio modeling of the structure and reactivity of zeolite catalysts are reviewed with both protons and transition metal cations as active species. Potential functions of the ion‐pair shell‐model type available for such studies are compiled. The reliability of the method is checked by comparison with periodic ab initio studies and by examining the convergence of the results with increasing size of the QM cluster. The problems tackled are: different types of Cu+ sites in the CuZSM‐5 catalyst and their properties, acidity differences between active sites in different zeolite framework structures (energies of deprotonation, NH3 adsorption energies), and proton mobility in acidic zeolites. The combined QM‐Pot approach made possible a full ab initio prediction of reaction rates for an elementary process on the surface of solid catalysts and of how these rates differ between different catalysts with the same active site. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1470–1493, 2000

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A theoretical study on the catalysis of Cu-exchanged zeolite for the decomposition of nitric oxide

Cited by 47 publications

References 44 publications

On the nature of spin- and orbital-resolved Cu+–NO charge transfer in the gas phase and at Cu(I) sites in zeolites

On the nature of spin- and orbital-resolved Cu+–NO charge transfer in the gas phase and at Cu(I) sites in zeolites

Correlation Between Catalytic Activity and Metal Cation Coordination: NO Decomposition Over Cu/Zeolites

Combining quantum mechanics and interatomic potential functions inab initio studies of extended systems

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