Evaluation of Brønsted Sites Inside the H-MOR Employing NH<sub>3</sub>: A Theoretical Study

Díaz, Lenin; Sierraalta, Aníbal; Nascimento, Marco Antônio Chaer; Áñez, Rafael

doi:10.1021/jp3116287

Cited by 14 publications

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“…The aforementioned results are corroborated by the experimental work of Lukyanov et al 15 and our previous results, 43 which showed that the T4 site is the position most probable to sit the Al atom and that the O2 atom is the most favorable one to attach the proton. Therefore, it is quite reasonable to assume that the amines will adsorb preferentially at T4.…”

Section: ■ Results and Discussionsupporting

confidence: 86%

“…The Brønsted sites in the acidic MOR structure (H-MOR) are created by replacing a Si atom by an Al atom at the four different T sites and adding a proton to the crystallographically distinct O atoms to compensate the negative charge. According to our previous results, 43 the proton binds preferentially to oxygen atoms O7a (T1) (Figure 2a), O3b (T2) (Figure 2a), O1b (T3) (Figure 2b), and O2b (T4) (Figure 2b). However, the acid site at T3 is energetically highly unfavorable in comparison with the other sites and for this reason will not be further considered.…”

Section: ■ Computational Details and Modelssupporting

confidence: 77%

“…According to our previous results, 43 Table 1 shows the average relative errors for the distances and angles of the H-MOR structure. The calculation results was compared with the experimental values from the X-ray spectrum of a synthetic MOR with a Si/ Al ratio of 7.…”

Section: ■ Computational Details and Modelsmentioning

confidence: 77%

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Theoretical Study of the Adsorption of Alkylamines in H-Mordenite: The Role of Noncovalent Interactions

et al. 2015

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The adsorption of NH 3 and alkylamines (MeNH 2 , Me 2 NH, and Me 3 N) on H-mordenite was studied using density functional theory (DFT) and the ONIOM method. The adsorption of the probe molecules was investigated with a set of functionals (B3LYP, B3LYP-D3, CAM-B3LYP, LC-ωPBE, and ωB97X-D) properly chosen to verify the importance of noncovalent interaction on the adsorption process. The adsorption energy increases with the size of the amine and with the type of functional used, according to the trend B3LYP-D3, ωB97X-D > CAM-B3LYP, LC-ωPBE > B3LYP. The noncovalent contribution to the adsorption energy is higher for Me 3 N, reaching 92 kJ/mol when B3LYP-D3 is used and 70 kJ/mol for ωB97X-D. Although the adsorption energies for each amine span a wide range of values depending on the functional used, the geometries of equilibrium are quite similar. The adsorption energies obtained by full geometry optimization of the complexes do not differ appreciably from those of single-point calculations using the geometries optimized at the B3LYP:UFF level of calculation, suggesting that for these systems the single-point strategy may be a reasonable alternative to reduce the computational cost of including noncovalent corrections in DFT results. A comparison was also made with the experimental differential heats of adsorption. At low coverage the computed E ads at the T4 site corrected for the basis set superposition (BSSE) and zero-point vibration energy errors exhibit the same trend of the experimental ΔH ads with the degree of methylation observed by Lee et al. (J. Am. Chem. Soc. 1996, 118, 3262−3268) as opposed to the one by Chen et al. (J. Catal. 1994, 146, 257−267). Also, the results obtained at the B3LYP-D3:UFF level of calculation including BSSE corrections strongly suggest that the falloff observed on the ΔH ads x coverage diagram, normally attributed to site heterogeneity, may be due to a combination of two factors: the number of molecules adsorbed on a given site and the acid site local configuration. ■ INTRODUCTIONOne of the main uses of alkylamines is as additives for the synthesis of colloidal semiconductor nanocrystals. 1 Furthermore, it has been reported that nitrogen hybrid zeolites with MeNH 2 , Me 2 NH, Me 3 N, EtNH 2 , n-PrNH 2 , and n-ButylNH 2 increase the basicity of MFI-type zeolites by the incorporation of N atoms into the framework. 2 As the first step of this process involves the adsorption of the amine on the zeolite framework, it is necessary to determine how this process is affected by the structure of the alkylamines.Mordenite (MOR) is one of the most abundant zeolites in nature, 3 and its protonic form (H-MOR) has been used in chemical processes such as hydrocarbon isomerization, 4 nparaffin cracking, 5 and alkylation reactions 6 and in the selective catalytic reduction (SCR) of NO. 7 The quantitative adsorption of alkylamines in H-MOR has been investigated using the microcalorimetry technique. 8,9 In these experiments the zeolite is kept at constant temperature in the cell where the probe molecu...

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Section: ■ Results and Discussionsupporting

confidence: 86%

Section: ■ Computational Details and Modelssupporting

confidence: 77%

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Theoretical Study of the Adsorption of Alkylamines in H-Mordenite: The Role of Noncovalent Interactions

et al. 2015

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“…Sierraalta and coworkers investigated the issue a decade ago. Using a 3T cluster model, they calculated the adsorption of NO, NO 2 , O 2 , NH 3 , and SO 2 over metal‐ZSM‐5.…”

Section: Theoretical Investigation Of the Adsorption Of Small Moleculmentioning

confidence: 99%

Theoretical investigation of NH₃‐SCR processes over zeolites: A review

Mao

Wang

2014

Int J of Quantum Chemistry

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The selective catalytic reduction (SCR) of NO x compounds with NH 3 is a hot topic in recent years. Among various catalysts, zeolites are proved to be efficient and promising for NH 3 -SCR, yet the whole processes and intrinsic mechanism are still not well understood due to the structural complexity of zeolites. With the improvement of theoretical chemistry techniques, quantum-chemical calculations are now capable of modeling the structure, acidity, adsorption, and ultimately reaction pathways over zeolites to some extent. In this review, a brief summary of relevant concepts of NH 3 -SCR is presented. Cluster approaches, embedded techniques, and periodic treatments are described as three main methods. Details of quantum-chemical investigations toward the key issues such as, the structure of active sites, the adsorption of small molecules, and the reaction mechanism of NH 3 -SCR over zeolites are discussed. Finally, a perspective for future theoretical research is given. V C 2014 Wiley Periodicals, Inc.

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“…The full-electron 6-31+G * basis set was used for NO molecule. The combinations of UFF and B3LYP in the ONIOM2 methodology have been successfully and widely used in literature to study metal/zeolite systems [18,[22][23][24][25][26][27][28]. We employed the recommended scaling factor 0.9648 [29] for NO bond stretching calculations.…”

Section: Computational Details and Modelsmentioning

confidence: 99%

Theoretical ONIOM2/DFT study of Pd/ZSM-5 catalyst: CO and NO adsorption

Sierraalta

Aòez

Rincón

2014

JCM

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In this study, we carried out two-layer ONIOM(DFT:MM) calculations to determine the adsorption enthalpies and vibrational frequencies of NO and CO molecules, on palladium exchanged zeolite (Pd/ZSM-5) catalyst. The results reveal that the local Al distribution near to Pd +2 influence the stretching frequencies as well as the adsorption enthalpies. The nine possible Al distributions studied can be gathered in two groups. One responsible for high CO and NO frequencies (υCO = 2146 cm −1 and υNO = 1880 cm −1 ) and the other one responsible for the low frequencies (υCO = 2127 cm −1 and υNO = 1840 cm −1 ). In general, the adsorption enthalpy of the CO is similar to the NO therefore; there is not a preferential adsorption of CO over the NO molecule.

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Evaluation of Brønsted Sites Inside the H-MOR Employing NH₃: A Theoretical Study

Cited by 14 publications

References 37 publications

Theoretical Study of the Adsorption of Alkylamines in H-Mordenite: The Role of Noncovalent Interactions

Theoretical Study of the Adsorption of Alkylamines in H-Mordenite: The Role of Noncovalent Interactions

Theoretical investigation of NH₃‐SCR processes over zeolites: A review

Theoretical ONIOM2/DFT study of Pd/ZSM-5 catalyst: CO and NO adsorption

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Evaluation of Brønsted Sites Inside the H-MOR Employing NH3: A Theoretical Study

Cited by 14 publications

References 37 publications

Theoretical Study of the Adsorption of Alkylamines in H-Mordenite: The Role of Noncovalent Interactions

Theoretical Study of the Adsorption of Alkylamines in H-Mordenite: The Role of Noncovalent Interactions

Theoretical investigation of NH3‐SCR processes over zeolites: A review

Theoretical ONIOM2/DFT study of Pd/ZSM-5 catalyst: CO and NO adsorption

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Evaluation of Brønsted Sites Inside the H-MOR Employing NH₃: A Theoretical Study

Theoretical investigation of NH₃‐SCR processes over zeolites: A review