Nitrogen physisorption

The micro-, meso- and macro-sized pores of a zeolite impact the catalyhc and separation properhes. Based on lUPAC terminology micropores are defined by pore sizes smaller than 2nm, mesopores are between 2 and 50 nm and pores greater than 50 nm are referred to as macropores. 

Although there are several methods for analysis of nitrogen physisorption data, the most commonly used is BET surface area. Because for microporous materials the boundary conditions for multilayer adsorption are not fulfilled, the calculated BET surface area has no physical meaning. Such data should be considered proportional to the total micropore volume rather than the specific surface area. The Tplot method can be used to calculate the micropore volume and the mesopore 

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Fig. 19.1 Nitrogen physisorption isotherms at 77 K for TiN nanoparticies (the numbers correspond to the sample code in Table 19.1).

TEM investigations support the interpretation of the nitrogen physisorption isotherms (Fig. 19.3). They show particles 5-20 run in diameter, whereas the particle size estimated from the specific surface area, assuming spherical particle morphology, is 7 nm. Indeed, the particle morphology for sample 7 is mostly spherical, but for some crystallites edges are discernible. 

The nitrogen physisorption isotherm and pore size distributions for the synthesized catalysts are shown in Figs. 3 and 4. The Type IV isotherm, typical of mesoporous materials, for each sample exhibits a sharp inflection, characteristic of capillary condensation within the regular mesopores [5, 6], These features indicate that both TS-1/MCM-41-A and TS-l/MCM-41-B possess mesopores and a narrow pore size distribution. 

Figure 3 Total surface area of the doped ceria samples plotted versus pore volume as determined by nitrogen physisorption.

XRD patterns were recorded on a Bruker D5005 diffractometer using a monochromated CuKa radiation (20 = 0.5-10 °). Nitrogen physisorption measurements at -196 °C were... 

The MWCNTs were purified using HF at 20 wt %. The samples were filtrated, washed with deionized water and dried at 100°C overnight. TGA analysis was carried out by heating at 10 °C/min from room temperature to 800°C. Nitrogen physisorption was used to determine BET surface area and BJH pore volume and size. 27Al MAS NMR spectra for the calcined samples were obtained. 

The surface area of the catalysts was measured by nitrogen physisorption (Sorptometer 1900, Carlo Erba). The fresh and regenerated samples were outgassed at 150°C and the spent samples at 100°C for 3 hours. The specific surface area was calculated with the Dubinin equation. 

The chemical compositions of the samples were obtained by ICP in a Varian 715-ES ICP-Optical Emission Spectrometer. Powder X-ray diffraction was performed in a Philips X pert diffractometer using monochromatized CuKa. The crystallinity of the zeolites was obtained from the intensity of the most intense reflection at 23° 20 considering the parent HZ5 sample as 100% crystalline. Textural properties were obtained by nitrogen physisorption at -196°C in a Micromeritics ASAP 2000 equipment. Surface areas were calculated by the B.E.T. approach and the micropore volumes were derived from the corresponding /-plots. Prior to the adsorption measurements the samples were degassed at 400°C and vacuum overnight. 

The 11 nm-sized Ti02 were crystallized using either hydrothermal or thermal methods from 100 nm, amorphous gel spheres. The Ti02 crystal and agglomerate sizes were determined by X-ray diffraction (Philip 1080) and transmission electron microscopy (JEOL JEM 2010), respectively. The surface area and chemistry of the nanostructured Ti02 were analyzed by nitrogen physisorption (Coulter SA 3100) and Fourier transform infrared spectroscopy (FTIR, Perkin-Elmer GX 2000). Metal catalyst was deposited by incipient... 

Suitable characterization techniques for surface functional groups are temperature-programmed desorption (TPD), acid/base titration [29], infrared spectroscopy, or X-ray photoemission spectroscopy, whereas structural properties are typically monitored by nitrogen physisorption, electron microscopy, or Raman spectroscopy. The application of these methods in the field of nanocarbon research is reviewed elsewhere [5,32]. 

EA = elemental analysis IR = infrared spectroscopy PXRD = powder X-ray diffraction BET = Brunauer-Emmett-Teller method (specific BET surface area) and BJH = Barrett-)oyner-Halenda method (determination of pore volume and diameter), both determined by nitrogen physisorption ... 

Nitrogen physisorption measurements indicate large internal surface area of 402 m /g and quite narrow distribution of pore sizes with peak maximum at 3.1 nm (Fig. 7). The framework wall thickness was estimated to be 1.9 nm. The oxidation state of Ge framework as probed with X-ray photoelectron spectroscopy (XPS) and time-of-fiight secondary ion mass spectroscopy (ToF-SIMS) techniques is close to zero. 

Nitrogen physisorption measurements evidence the permanent mesoporosity of the NU-GeSi-A materials (Fig. 11). All the N2 adsorption-desorption isotherms... 

The surface areas and pore properties of both the supercritical fluid extracted and the calcined samples were analysed by nitrogen physisorption at 77K using a Quantachrome Auto-Sorbl analyser. The powder X-ray diffraction patterns of both samples were recorded using a SHIMADZU XRD-600 powder X-ray diffractometer, where Cu target Ka-ray was used as the X-ray source. 

In this study we present the first in-situ formation of a ternary transition metal oxide within the pores of MCM-48 silica. XRD measurements showed the preservation of the host structure as well as the formation of 5-6 nm small particles. In addition, the analysis of nitrogen physisorption data revealed the existence of mesopores with smaller pore diameters and surface areas in comparison to the pristine phase, which can be attributed to the introduction of the Co/Fe/O phase into the pores. First qualitative XANES and EXAFS analyses support the formation of CoFe204 nanoparticles. TEM investigations on particle size and structure are in progress. To learn more about the properties of the oxide nanoparticles Mossbauer and magnetic measurements have to be carried out, which are planned for the future. 

Nitrogen physisorption of the Ge-ZSM-5 sample revealed a considerable contribution of mesopores to the total pore volume, accompanied by a drop in micropore volume of 20%. In a study of the catalytic activity of these materials it was found that the increased mesoporosity of Ge-ZSM-5 had a beneficial effect on the catalytic activity in a series of acid-catalysed reactions.1771 It was observed that the presence of germanium in the framework does not change the strength of the acid sites but, instead, decreases the extent of deactivation from coke residues formed upon reaction. The microporous domains only have short diffusional lengths, but the shape selectivity ascribed to the zeolitic channels is still fully... 

Porous texture of the different materials was all characterized using nitrogen (N2) physisorption at 77 K and up to a pressure of 0.1 MPa. From the nitrogen physisorption data, obtained with the High Speed Gas Sorption Analyser NOVA 1200, the BET-surface area, total pore volume, microporous volume and t-volume were derived. The BET surface area (SBet) is the surface area of the sorbent according to the model formulated by Brunauer et al. [8] for planar surfaces. 

Catalyst surface areas prior to reaction were determined by application of the BET method to nitrogen physisorption isotherms determined at 77K. 

Nitrogen physisorption methods for total surface area (BET), and more recently macropore surface area determination (t-plot) are used to quantify relationships of the amount and type (zeolite, matrix) of surface present. Nitrogen and mercury pore size distribution (NPSD HGPSD) are used to determine sizes of pores within the catalyst. Bulk, particle, and skeletal densities can be measured with standard volumetric apparatus or more recently with sophisticated pychnometers using helium as a fill gas. 

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