Base property of high silica MFI zeolites modified with various alkyl amines

Guo, Juan; Han, Ai-Jie; Yu, Hui; Dong, Jin; He, Heyong; Long, Yun-Ze

doi:10.1016/j.micromeso.2006.03.046

Cited by 21 publications

(16 citation statements)

References 30 publications

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“…One of the main uses of alkylamines is as additives for the synthesis of colloidal semiconductor nanocrystals . 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 . 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.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…The amount of carbon, however, is almost constant, indicating that the aminopropyl group is not released completely. Therefore, pyrolytic conversion of the materials in an atmosphere of nitrogen as investigated in this work differs from silica (MFI type zeolite) modified with alkyl amines where a major loss of hydrocarbons was already observed after pyrolysis in helium at temperatures ≤ 300°C [28].…”

Section: Changes Of the Amine Group Content During Pyrolysismentioning

confidence: 99%

“…Si-N bond formation was observed already after treatment of the silica with amines in the gas phase at 50 °C by IR and NMR. The material pre-treated in helium at 500°C and loaded with CO 2 at 80 °C showed highly decreased CO 2 sorption compared to material pretreated at 300°C [28,29]. Therefore, the temperature stability of amine groups in cross-linked polysiloxanes should be investigated since the integration of the amine groups in the material can be different.…”

Section: Introductionmentioning

confidence: 99%

Tailoring amine functionalized hybrid ceramics to control CO2 adsorption

Prenzel

Wilhelm

Rezwan

2014

Chemical Engineering Journal

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“…Zeolites, having nanopores less than 2 nm in diameter, are widely used in adsorption processes and shape-selective catalysis, as well as in emerging applications such as molecular sieving membranes, sensors, and low- k dielectric materials. − By incorporating covalently bound (as opposed to physisorbed) organic groups within the micropores, these highly ordered materials can potentially be converted to organic–inorganic hybrids for a diverse range of new applications. There are three main routes − for functionalizing mesoporous materials and zeolites: (i) direct synthesis via sol–gel or hydrothermal processes involving co-condensation of organotrialkoxysilanes R-Si(OR′) 3 or organochlorosilanes R-SiCl 3 with tetraalkoxysilanes (Si-(OR) 4 ) that are the primary silica source for mesoporous material formation, (ii) postsynthesis modification via grafting the material with silane coupling agents such as NH-(SiR) 2 , Cl-SiR 3 , or RO-Si-R′, and (iii) postsynthesis reaction with organic molecules. The first two routes present difficulties in their application to zeolite materials.…”

Section: Introductionmentioning

confidence: 99%

“…The observed alcohol loading was strongly correlated with the concentration of internal silanol defects in the zeolite. Two previous reports , studied the properties of high-silica MFI modified with methylamine (MA). Based on FT-IR and NMR characterization, the formation of Si–N–Si linkages in the framework was proposed.…”

Section: Introductionmentioning

confidence: 99%

Preparation and Gas Adsorption Characteristics of Zeolite MFI Crystals with Organic-Functionalized Interiors

2011

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We show that the selective gas adsorption properties of pure-silica MFI zeolite crystals are significantly altered by modifying their internal pore structure with molecules such as aliphatic alcohols, aromatic alcohols, amino-alcohols, and amines. NMR and TGA/DSC characterization indicates that the functional groups are chemisorbed to the internal pores, and the organic molecule loading is strongly dependent on the concentration of internal silanol sites. Adsorption isotherms of CO2, CH4, and N2 are measured for the functionalized samples up to 400 kPa. In the low pressure region (1–10 kPa), the organic-modified materials show gas adsorption behavior significantly different from that of the bare zeolite MFI, ranging from an enhancement in CO2/CH4 sorption selectivity in the amine-functionalized materials to an enhancement in CH4 adsorption in the aromatic-functionalized material. The CO2/N2 sorption selectivity decreases for all the modified materials compared to bare zeolite MFI. This investigation of organic-modified MFI zeolites points toward the tuning of adsorption and molecular sieving behavior of zeolites through internal modification of the pores.

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Base property of high silica MFI zeolites modified with various alkyl amines

Cited by 21 publications

References 30 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

Tailoring amine functionalized hybrid ceramics to control CO2 adsorption

Preparation and Gas Adsorption Characteristics of Zeolite MFI Crystals with Organic-Functionalized Interiors

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