Pore Size Analysis of MCM-41 Type Adsorbents by Means of Nitrogen and Argon Adsorption

Neimark, Alexander V.; Ravikovitch, Peter I.; Grün, M.; Schüth, Ferdi; Unger, Klaus K.

doi:10.1006/jcis.1998.5748

Cited by 333 publications

(307 citation statements)

References 38 publications

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“…From a predictive viewpoint the density profile required for the evaluation of D to maybe obtained by an established theory such as nonlocal density functional theory ͑NLDFT͒, that has shown considerable success in modeling adsorption isotherms in mesoporous materials such as MCM-41 and microporous carbons, and has been verified against simulation. [46][47][48][49] For the present purpose, however, we use the profiles obtained from simulation in order to explore and test the result in Eq. ͑21͒.…”

Section: Transport Modelmentioning

confidence: 99%

Molecular transport in nanopores

Bhatia

Nicholson

2003

The Journal of Chemical Physics

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Simulation of the transport of methane in cylindrical silica mesopores have been performed using equilibrium and nonequilibrium molecular dynamics (NEMD) as well as dual control volume grand canonical molecular dynamics methods. It is demonstrated that all three techniques yield the same transport coefficient even in the presence of viscous flow. A modified locally averaged density model for viscous flow, combined with consideration of wall slip through a frictional condition, gives a convincing interpretation of the variation of the transport coefficient over a wide range of densities, and for various pore sizes and temperatures. Wall friction coefficients extracted from NEMD simulations are found to be consistent with momentum transfer arguments, and the approach is shown to be more meaningful than the classical slip length concept.

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Section: Transport Modelmentioning

confidence: 99%

Molecular transport in nanopores

Bhatia

Nicholson

2003

The Journal of Chemical Physics

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“…[1][2][3]. The interplay of finite size and surface effects strongly modifies the phase behavior of such confined fluids [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] in comparison with the bulk. The vapor to liquid transition is shifted ("capillary condensation"), as well as critical points [3,4,9,12].…”

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confidence: 99%

Rounding of Phase Transitions in Cylindrical Pores

et al. 2010

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Phase transitions of systems confined in long cylindrical pores (capillary condensation, wetting, crystallization, etc.) are intrinsically not sharply defined but rounded. The finite size of the cross section causes destruction of long range order along the pore axis by spontaneous nucleation of domain walls. This rounding is analyzed for two models (Ising/lattice gas and Asakura-Oosawa model for colloid-polymer mixtures) by Monte Carlo simulations and interpreted by a phenomenological theory. We show that characteristic differences between the behavior of pores of finite length and infinitely long pores occur. In pores of finite length a rounded transition occurs first, from phase coexistence between two states towards a multi-domain configuration. A second transition to the axially homogeneous phase follows near pore criticality. PACS numbers: 64.75Jk, 64.60.an, 05.70Fh, 02.70Tt Fluids and fluid mixtures in nano-and microporous materials (pore diameters from 1 nm to 150 nm) play important roles in various industries (extracting oil and gas from porous rocks; use as catalysts or for mixture separation in the chemical and pharmaceutical industry; nanofluidic devices, etc.) [1][2][3]. The interplay of finite size and surface effects strongly modifies the phase behavior of such confined fluids [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] in comparison with the bulk. The vapor to liquid transition is shifted ("capillary condensation"), as well as critical points [3,4,9,12]. Effects of wetting [20] on phase coexistence give rise to interesting patterns (plugs versus capsules versus tube structures etc. [7]). However, although various phase diagrams (different from the bulk) have been proposed (e.g. [1,3,7,9,12,13,17]), many aspects hitherto are not well understood. E.g., the "critical point" where adsorption/desorption hysteresis vanishes seems to be systematically lower than the critical temperature where the density difference between the vapor-like and liquid-like states vanishes [12], in contrast to what theories have predicted [14].However, a crucial aspect (stressed only in a few pioneering studies [3,8], and in the context of Ising/lattice gas models [21][22][23]) is the rounding of all transitions, caused by the quasi-one-dimensional character of a fluid in a long cylindrical pore with cross-sectional radius R. With the current progress of producing pores of wellcontrolled diameter varying from the nanoscale (carbon nanotubes [23][24][25]) to arrays of pores in silicon wafers [26], up to 150 nm wide and of well-controlled length, experiments become feasible which are not plagued by effects of random disorder, which occur in porous glasses [1,27]. Thus, it is important to understand the phase transitions in pores more precisely, considering both the radius R and the length L of the pore as variables (the important role of L has so far been largely disregarded). In the present Letter, we elucidate the rounding of vaporliquid type transitions in cylindrical pores, based on Monte Carlo sim...

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“…Surface area using the BET model was used in the pressure range 0.05 P/P 0 -0.25 P/P 0 [19], and pore size distribution was determined according to non-local density functional theory (NLDFT) models [20]. Incorporation evidence was performed using ultraviolet-visible spectrometer lambda 35 Perkin Elmer with an integration sphere attached to record the diffuse reflectance spectrum (DRS-UV) in the visible region, from 400 to 700 nm.…”

Section: Catalyst Characterizationmentioning

confidence: 99%

“…Mesoporous MCM-41 silica prepared with cetyltrimethylammonium bromide (CTABr) as pore director leads to a mean diameter of 4.0 nm approximately, confirmed by XRD and TEM experiments [23]. Through nitrogen adsorption, it is possible to determine pore size; NLDFT [20] or the Barrett-Joyne-Halenda (BJH) method [24] are two approaches for the determination of the pore size of mesoporous materials. The latter underestimates the pore size of a cylindrical shape (like MCM-41 pores), while NLDFT hasa better correlation, giving pore diameters around 4.0 nm for MCM-41 prepared with CTABr as a pore director [25].…”

Section: Catalyst Characterizationmentioning

confidence: 99%

Single Wall Carbon Nanotubes Synthesis through Methane Chemical Vapor Deposition over MCM-41–Co Catalysts: Variables Optimization

Rodriguez

López

Giraldo

2018

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MCM-41-Co catalysts were tested in the synthesis of single wall carbon nanotubes (SWCNTs) through methane chemical vapor deposition (CVD), varying total cobalt content, synthesis temperature, methane flow rate, and deposition time. All variables showed a relationship with total carbon deposition, graphitic quality according to Raman results. Cobalt content showed a maximum activity at 4%, but the structural quality is best at 3%. Flow rate does not affect the quality up to 300 cm 3 min −1 , but deposition time leads to the formation of highly disordered carbon species passing methane for periods longer than 30 min, concluding that optimal variables are a methane deposition temperature of 800 • C, a 300 cm 3 min −1 methane flow rate, and a 30 min of methane injection time, leading to a 5.4% carbon mass content and 5.1 G/D area ratios.

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Pore Size Analysis of MCM-41 Type Adsorbents by Means of Nitrogen and Argon Adsorption

Cited by 333 publications

References 38 publications

Molecular transport in nanopores

Molecular transport in nanopores

Rounding of Phase Transitions in Cylindrical Pores

Single Wall Carbon Nanotubes Synthesis through Methane Chemical Vapor Deposition over MCM-41–Co Catalysts: Variables Optimization

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