In situ formation of the micro- and mesoporous structures MFI and MCM-41 was obtained using a two-template syntheses gel system [C6H13(CH3)3NBr and C14H29(CH3)3NBr]. The mixed phases were obtained by optimizing template concentrations and reaction temperatures. Constant temperature syntheses as well as sequential high/low or low/high temperature strategies were performed successfully. It was found that the relative amounts of the two structures MFI and MCM-41 in the final products can be controlled by varying the ratio of the templates and by tuning the synthesis temperature. Characterization results indicate that phases of varying complexity were obtained.

Characterization of water saturated mesoporous MCM-41 materials with narrow pore-size distributions by H-1 NMR revealed two temperature transitions above 373 K. The first transition temperature (373-391 K) was assigned to the boiling point of ''free'' water within the pores, while the second transition temperature (408-413 K) was associated with desorption of less mobile ''surface'' water. The boiling point, T-b, of the ''free'' water increased with decreasing pore diameter, D (Angstrom), according to: T-b = a(0)+a(1) D-1+a(2) D-2 with a(0) = (373 +/- 1) K, a(1) = (70 +/- 59) K .Angstrom and a(2) = (5.7 +/- 1.2).10(3) K .Angstrom(2).

The pore size distribution of four commercial silica materials saturated with water have been derived from experimental H-1 NMR intensity vs temperature curves (IT-curves) of the confined water. The observed melting points or transition temperatures of benzene and cyclohexane confined in the same materials are shown to be consistent with corresponding data obtained from the water IT-curves. In general, the freezing point depression (Delta T) of these fluids can be related to the pore radius R in accordance with a modified Gibbs-Thompson equation: Delta T = K/(R + d), where K and d are constants characteristic of the confined fluid. The melting point depressions of benzene and cyclohexane are shown to be more sensitive to pore radius than that of water; i.e., the two former have a larger K-value. Moreover, the average pore radius of these materials can be estimated from H-1 NMR chemical shift measurements of the benzene-saturated samples. Simulation of H-1 NMR spectra of benzene confined in mixtures of silica (mesopores) and zeolite (micropores) will be presented.

A mesoprorous MCM-48 is synthesised with an Si : Al ratio of 22, without observing octahedral aluminnium in its as-synthesised form or after template removal by calcination at 540 °C.

The aim of the present study is to derive a mathematical pore size distribution function containing a limited number of adjustable parameters. These parameters can be determined exclusively from H-1 NMR measurements. Regular mesoporous MCM-41 materials with different pore sizes, ranging from 20 to 30 Angstrom, were synthesized and characterized by HREM, N-2 adsorption, and H-1 NMR. The pore sizes determined by Nf adsorption and HREM were in good agreement. The H-1 NMR technique was used to determine the freezing point of water enclosed in water-saturated samples. By combining N-2 adsorption and H-1 NMR measurements, a simple relation was found between the freezing point depression (Delta T) and the pore radius (R(p)): Delta T = K/(R(p) - t(f)) with t(f) = 3.49 +/- 0 36 Angstrom. The observation that t(f) not equal 0 is tentatively explained by the formation of a surface layer of nonfreezing water of thickness t(f), which effectively reduces the actual pore radius from R(p) to R(p) - t(f). A mathematical model is derived which enables the pore size distribution to be determined from H-1 NMR intensity vs temperature measurements of water-saturated materials. The pore size distribution of amorphous' silica determined independently by H-1 NMR and N-2 adsorption agreed well. However, the pore size of a microporous VPI-5 material (R(p) = 6.05 Angstrom) could not be predicted by the present model.

1H Nuclear magnetic resonance (NMR) spin-echo measurements at 268 K have been performed on water-saturated mesoporous MCM-41 materials. The pores have cylindrical geometry with diameters in the range 18–40 Å and length of approximately 1 mm. Using appropriate model calculations the self-diffusion coefficient (D) of water within the pore was estimated from the Carr-Purcell-Meiboom-Gill (CPMG) spin-echo envelope curves. D was found to be in the range 0.17·10−6 to 2.3·10−6 cm2/s and could be expressed by an equation of the form D−1∝D∞−1+α·lc−2 where D∞ is the self-diffusion coefficient of bulk water (lc = ∞) and α = (2.68 ± 0.14)·10−5s. The low values for the diffusion coefficients—compared to the diffusion coefficient of bulk water — are related to the strong interaction of the water molecules with the pore surface. Moreover, the spin-spin relaxation rate (1T2) was related to lc by application of the Bloembergen-Purcell-Pound (BPP) model.

Purely siliceous MCM-41 materials with different pore sizes were synthesised. The obtained nitrogen isotherms of these materials varied from a “type I-like” isotherm (small pore size) over a reversible type IV isotherm (intermediate pore size) to a typical type IV isotherm, which shows pore condensation with hysteresis. Similar types of transition states and hysteresis curves are observed by 1H nuclear magnetic resonance (NMR) by monitoring the proton signal intensity of the mobile water molecules confined in the pores versus temperature. The consistency observed between the two methods makes 1H NMR a valuable additional technique for characterisation of mesoporous materials.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPore Size Determination of MCM-51 Mesoporous Materials by means of 1H NMR Spectroscopy, N2 adsorption, and HREM. A Preliminary StudyRalf Schmidt, Eddy Walther Hansen, Michael Stoecker, Duncan Akporiaye, and Ole Henrik EllestadCite this: J. Am. Chem. Soc. 1995, 117, 14, 4049–4056Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://pubs.acs.org/doi/10.1021/ja00119a021https://doi.org/10.1021/ja00119a021research-articleACS PublicationsRequest reuse permissionsArticle Views2632Altmetric-Citations273LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Combining spin-lattice relaxation time measurements and signal intensity measurements vs temperature of water confined in mesoporous molecular sieves (MCM-41 materials) gives information regarding the activation enthalpy of bound water and the width of the log-normal distribution of correlation times of the water molecules. Three different water ''phases'' are observed which have significantly different relaxation strength. The overall spin-lattice relaxation rate is shown to be strongly dependent on the number of silanol protons. ''Analytical'' formulas for the average spin-lattice relaxation rates are derived.

A cubic MCM-48 and a hexagonal MCM-41 material were synthesised. The pore ordering was confirmed by X-ray powder diffraction and HREM studies. The pore size of the materials was determined to 2.9 nm for MCM-41 and 2.5 nm for MCM-48 by N-2 adsorption and by measuring the freezing depression of water enclosed in the pores by H-1 NMR. The self diffusion coefficient of water confined in the pores of MCM-48, determined by 1H NMR spin-echo measurements, was found to be significantly larger compared to that of MCM-41. Si-29 MAS NMR showed a significant higher number of Q(3) species (Si(3OSi)OH) for MCM-48 in the as-synthesised state compared to MCM-41.

A cubic member of the M41S family with a three-dimensional pore system, denoted as MCM-48, was synthesised. By combining X-ray powder diffraction (XRD) with high-resolution electron microscopy (HREM), a cubic symmetry with an Ia3d space group was determined for the as-synthesised and the calcined MCM-48 material. Upon calcination the unit cell decreased from around 10.09 nm to about 8.1 nm. The overall pore structure was found to be quite unaffected by local variations in the structure and the decrease in the unit cell size upon calcination.

A crystalline mesoporous member of the MCM-41 family has been synthesised with a Si:Al ratio as low as 8.5:1, without observing octahedral aluminium.

H-1 NMR measurements on a new family of mesoporous molecular sieves, designated MCM-41, saturated with water show abrupt changes in the signal intensity of the water signal at specific temperatures, denoted as transition temperatures. A model equation is presented describing the intensity vs temperature behavior. Similar transition phenomena are also observed in line width vs temperature. A linear relationship between the spin-lattice relaxation rate (at -10 degrees C) and the first transition temperature, as determined from the intensity measurements, is found. This behavior is expected if it is assumed that the transition temperature can be predicted by Kelvin's equation and that the spin-lattice relaxation rate is proportional to the inverse of the pore radius, as previously reported in the literature.

MCM-41 materials with bulk Si/Al ratios of 18, 9 and 4 and having different pore sizes were synthesised and characterised by XRD and HREM. The long range pore ordering of the obtained materials increased with the aluminium content. TGA experiments reveal systematic changes in the interaction of the template with silanol groups observed by Si-29 MAS NMR and aluminium species present. Removal of the template using liquid phase extraction methods instead of calcination had significant impact on the final material.