Diffusion processes in mesoporous adsorbents probed by NMR

Valiullin, Rustem; Dvoyashkin, Muslim

doi:10.1007/s10450-007-9053-1

Cited by 13 publications

(10 citation statements)

References 35 publications

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“…8 shows the diffusivity data of cyclohexane in an activated carbon (MA2 116,117 ) with interconnected micro-and mesopores. Similarly as observed with the purely mesoporous materials, [111][112][113][114] for a given external pressure, the diffusivities measured on the adsorption branch (i.e. after pressure increase) were notably different from those on the desorption branch.…”

Section: Diffusion Measurement Over Microscopic Dimensions 31 Pulsed ...supporting

confidence: 60%

“…Depending on their ''history'', molecular ensembles are thus found to accommodate porous systems in notably different configuration over essentially infinite times, 112 with their diffusivities as a characteristic finger print for the given configuration. 113,114 This strong influence of the ''history'', i.e. of the protocol how the external parameters have been varied before the actual ones were established, has recently been also observed with hierarchical materials, i.e.…”

Section: Diffusion Measurement Over Microscopic Dimensions 31 Pulsed ...mentioning

confidence: 78%

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In situ study on molecular diffusion phenomena in nanoporous catalytic solids

2010

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As an omnipresent phenomenon in nature, diffusion is among the rate-determining processes in many technological processes. This is in particular true for catalytic conversion in nanoporous materials. We provide a critical review of the possibilities of exploring diffusion phenomena over microscopic dimensions in such media by direct experimental observation. By monitoring the probability distribution of molecular displacements as a function of time, the pulsed field gradient technique of NMR (PFG NMR) records the rate of molecular re-distribution. By varying the observation time, PFG NMR is thus able to trace even hierarchies of transport resistances as occurring, e.g., in catalyst particles in the form of binder-compacted assemblages of zeolite crystallites. Alternatively, and complementary to this information, interference microscopy (IFM) and IR microscopy (IRM) are able to follow the evolution of intracrystalline concentration profiles during uptake and release. This allows, in particular, an accurate quantification of the transport resistances on the surface of the individual crystallites and of the probability that reactant molecules from the gas phase, upon colliding with the external surface, are able to penetrate through such "surface barriers" into the crystal bulk phase. Being able to distinguish between different molecular species, IRM is able to record the evolution of intracrystalline concentration profiles even during multi-component adsorption and catalytic reactions (169 references).

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Section: Diffusion Measurement Over Microscopic Dimensions 31 Pulsed ...supporting

confidence: 60%

Section: Diffusion Measurement Over Microscopic Dimensions 31 Pulsed ...mentioning

confidence: 78%

In situ study on molecular diffusion phenomena in nanoporous catalytic solids

2010

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“…The mechanism of adsorption was elucidated and the rate‐limiting step was investigated. A two resistances model based on external film diffusion and internal pore diffusion was applied; according to the physical adsorption phenomena, as adsorption itself is much faster than diffusion it cannot be treated as a rate limiting step . In this study the model proposed by Reichenberg and the model of Weber and Morris were used.…”

Section: Methodsmentioning

confidence: 99%

Recovery of free amino acids and muscle proteins from codfish (Gadus morhua L.) salting wastewater by sorption on Amberlite XAD16

Ferraro

Jorge

Cruz

et al. 2013

J of Chemical Tech & Biotech

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BACKGROUND The objective of this research was the valorization of an agro‐food industry residue, namely codfish salting wastewater, through the recovery of valuable bioactive compounds. Approximately 200 L of salted wastewater are generated for each ton of fresh codfish, carrying protein and free amino acids at a concentration of c. 10 g L−1, and sodium chloride (NaCl) at c. 250 g L−1. RESULTS Protein and free amino acids were selectively recovered by sorption with the Amberlite XAD16 resin. Food‐grade acetone was used to elute amino acids while a solution of sodium hydroxide (NaOH) desorbed protein. Recovery of protein and of hydrophobic to neutral amino acids was 100%; NaCl was also partially recovered from the salting wastewater, at a level of 33%. Kinetics and mechanisms of adsorption and desorption were investigated. CONCLUSIONS The process implemented can be considered as a valuable management option for codfish salting wastewater, it can contribute to the fish industry sustainability and can serve as a source of nutrients. Free amino acids and protein extracts can find application in animal and human nutrition through incorporation into functional food and drinks, as well as in cosmetics and in pharmaceutical formulations. © 2013 Society of Chemical Industry

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“…A problem is to find a relation between the pore network model and the real material. Structural properties of the porous material can be obtained based on various experimental methods, such as gas adsorption (with nitrogen as the standard adsorptive) [351][352][353][354], mercury porosimetry [320, 345-348, 354, 355], small-angle X-ray scattering, electron and X-ray micro-and nanotomography [311-319, 321, 426, 437], and nuclear magnetic resonance [438][439][440][441][442]. The next problem is the pore network reconstruction from measurement data.…”

Section: Pore Network Modelsmentioning

confidence: 99%

Connecting theory and simulation with experiment for the study of diffusion in nanoporous solids

et al. 2021

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Nanoporous solids are ubiquitous in chemical, energy, and environmental processes, where controlled transport of molecules through the pores plays a crucial role. They are used as sorbents, chromatographic or membrane materials for separations, and as catalysts and catalyst supports. Defined as materials where confinement effects lead to substantial deviations from bulk diffusion, nanoporous materials include crystalline microporous zeotypes and metal–organic frameworks (MOFs), and a number of semi-crystalline and amorphous mesoporous solids, as well as hierarchically structured materials, containing both nanopores and wider meso- or macropores to facilitate transport over macroscopic distances. The ranges of pore sizes, shapes, and topologies spanned by these materials represent a considerable challenge for predicting molecular diffusivities, but fundamental understanding also provides an opportunity to guide the design of new nanoporous materials to increase the performance of transport limited processes. Remarkable progress in synthesis increasingly allows these designs to be put into practice. Molecular simulation techniques have been used in conjunction with experimental measurements to examine in detail the fundamental diffusion processes within nanoporous solids, to provide insight into the free energy landscape navigated by adsorbates, and to better understand nano-confinement effects. Pore network models, discrete particle models and synthesis-mimicking atomistic models allow to tackle diffusion in mesoporous and hierarchically structured porous materials, where multiscale approaches benefit from ever cheaper parallel computing and higher resolution imaging. Here, we discuss synergistic combinations of simulation and experiment to showcase theoretical progress and computational techniques that have been successful in predicting guest diffusion and providing insights. We also outline where new fundamental developments and experimental techniques are needed to enable more accurate predictions for complex systems.

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Diffusion processes in mesoporous adsorbents probed by NMR

Cited by 13 publications

References 35 publications

In situ study on molecular diffusion phenomena in nanoporous catalytic solids

In situ study on molecular diffusion phenomena in nanoporous catalytic solids

Recovery of free amino acids and muscle proteins from codfish (Gadus morhua L.) salting wastewater by sorption on Amberlite XAD16

Connecting theory and simulation with experiment for the study of diffusion in nanoporous solids

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