RESUMO
Siliceous SBA-15 mesoporous molecular sieves were functionalized with different amounts of 3-aminopropyl-trimethoxysilane. To obtain a more detailed insight into the material properties of the prepared samples, their textural parameters were combined with results of thermal analysis. Adsorption isotherms of carbon dioxide on parent and functionalized SBA-15 were measured in the temperature range from 273 to 333 K. From the temperature dependence of CO(2) isotherms the isosteric adsorption heats of CO(2) were determined and discussed. Information about the surface energetic heterogeneity caused by tethered 3-aminopropyl groups were obtained from CO(2) adsorption energy distributions calculated using the theoretical CO(2) adsorption isotherms derived from the non-local density functional theory. The values of isosteric heats and the energy distributions of CO(2) adsorption detect highly energetic sites and enabled quantification of their concentrations.
RESUMO
Mesoporous aluminosilicate adsorbents for carbon dioxide were prepared by the grafting of aluminium into SBA-15 silica using an aqueous solution of aluminium chlorohydrate. As the ion exchange sites are primarily associated with the presence of tetrahedrally coordinated aluminium, extra-framework aluminium on the SBA-15 surface was inserted into the silica matrix by a treatment with an aqueous solution of NH(4)OH. Synthesized mesoporous aluminosilicate preserving all the characteristic features of a mesoporous molecular sieve was finally modified by the alkali metal cation exchange. To examine carbon dioxide adsorption on prepared materials, adsorption isotherms in the temperature range from 0 °C to 60 °C were measured. Based on the known temperature dependence of adsorption isotherms, isosteric adsorption heats giving information on the surface energetics of CO(2) adsorption were calculated and discussed. The comparison of carbon dioxide isotherms obtained on aluminosilicate SBA-15, aluminosilicate SBA-15 containing cations Na(+) and K(+) and activated alumina F-200 reveals that the doping with sodium or potassium cations dramatically enhances adsorption in the region of equilibrium pressures lower than 10 kPa. Therefore, synthesized aluminosilicate adsorbents doped with Na(+) or K(+) cations are suitable for carbon dioxide separation from dilute gas mixtures.
RESUMO
Novel functionalized adsorbents for CO(2) separation were synthesized by grafting 3-aminopropyl, 3-(methylamino)propyl, or 3-(phenylamino)propyl ligands in the delaminated zeolite ITQ-6. On the basis of the texture parameters determined from nitrogen adsorption isotherms recorded at 77 K and the results of chemical analysis, physicochemical properties of functionalized ITQ-6 were evaluated and compared with those of mesoporous SBA-15 silica functionalized with the same ligands. To examine carbon dioxide adsorption on functionalized materials, adsorption isotherms at 293 K were measured. To obtain information on the surface energetics of CO(2) adsorption on selected samples, isotherms were taken in the temperature range from 273 to 333 K and adsorption isosteres were calculated. Isosteric adsorption heats determined from the slope of adsorption isosteres proved that all of the 3-aminopropyl ligands in ITQ-6 take part in CO(2) adsorption. It was found that in the whole region of CO(2) pressures the efficiency of the amine ligand, defined as the number of adsorbed CO(2) molecules per one amine ligand, is higher for functionalized ITQ-6 than for functionalized SBA-15 silica.
