Resistance to the transport of H2 through the external surface of as-made and modified silicalite-1 (MFI)
| Autor: | Federica Ciuchi, Gn Kalantzopoulos, Raffaele Giuseppe Agostino, Alfonso Policicchio, Ivana Krkljus, Michael Hirscher, Giovanni Golemme, E. Maccallini |
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| Rok vydání: | 2016 |
| Předmět: |
Thermal desorption spectroscopy
Chemistry Diffusion Thermal desorption Sorption 02 engineering and technology General Chemistry 010402 general chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics 01 natural sciences 0104 chemical sciences Contact angle Adsorption Chemical engineering Mechanics of Materials Desorption Organic chemistry Surface modification General Materials Science 0210 nano-technology |
| Zdroj: | Microporous and Mesoporous Materials. 220:290-297 |
| ISSN: | 1387-1811 |
| Popis: | The adsorption and the thermal desorption of hydrogen in as-made and surface-modified silicalite-1 (MFI) loose crystals has been studied to shed light on the relation between the outer surface barrier and the transport of mass through it. The four different surface modifications can be probed by the change in the contact angle of water, but do not produce any apparent change in the morphology and the structure of the crystals. The H 2 adsorption isotherms in a Sievert's-type apparatus at 77 K and up to 8 MPa on the pristine and the modified silicalite-1 samples are almost overlapping, showing that the modifications involve the external surface of the samples. However the diffusion coefficients of H 2 , as derived from the sorption kinetics, evidence different sorption rates of H 2 into the different silicalite-1 samples. In particular the unmodified silicalite-1 sample presents the lowest diffusion coefficient and yields the highest H 2 desorption temperature in Thermal Desorption Spectra acquired at 0.03 K/s. The observed phenomena have been attributed to the surface silanols on the outer surface of the as-made silicalite-1 crystals, which are either eliminated or greatly reduced in number by the modifying agents. Polar and hydrophilic silanol groups bind frozen water molecules on the outer surface of as-made crystals which hinder the diffusion of hydrogen, and interact more strongly with the H 2 molecules. This provides sorption sites with higher potential energy barriers, and at the same time physically obstructs the pore entrances of the molecular sieve. The surface modification of porous fillers is of interest for the manufacture of mixed matrix membranes, for the improvement of the performance of pressure swing adsorption processes, and for gas storage applications. |
| Databáze: | OpenAIRE |
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