Nitrogen sorption isotherms

Figure 3. Nitrogen sorption isotherms, DFT pore size distributions (inset) and XRD patterns (inset) of MCM-41-IBU obtained after different immersion times...

Fio. II. Nitrogen sorption isotherm of two catalysts made from the same hydrogel, i.e., one very active, the other completely dead. The active sample was specially dried by extraction with an organic solvent of low surface tension to protect the larger pores. 

Figure 2.1 Nitrogen sorption isotherms at 77 Kfor a purely microporous (+), mesoporous ( ) and macroporous (a) silica.

Figure 2.2 Nitrogen sorption isotherm (77 K) on Kieselgel 60, treated at 973 K for 17 h.

L44 Lawrence, C. D. The Interpretation of Nitrogen Sorption Isotherms on Hydrated Cement (Techn. Rpt 530), 28 pp.. Cement and Concrete Association, Slough, UK (1980). 

Nitrogen sorption isotherms of the three parent silica supports are presented in Figure 1, and computed textural properties are reported in Table 1. Pore radii were determined by means of Barrett-Joyner-Halenda (BJH) and Broekhoff-De-Boer (BdB) calculations. Chain loadings ng are reported in Table 2. 

Pore size Pa and Pd were calculated from nitrogen sorption isotherm based on BJH model from adsorption branch and desorption branch, respectively. 

The texture properties of the ultrathin porous glass membranes prepared in our laboratory were initially characterized by the equilibrium based methods nitrogen gas adsorption and mercury porosimetry. The nitrogen sorption isotherms of two membranes are shown in Fig. 1. The fully reversible isotherm of the membrane in Fig. 1 (A) can be classified as a type I isotherm according to the lUPAC nomenclature which is characteristic for microporous materials. The membrane in Fig. 1 (B) shows a typical type IV isotherm shape with hysteresis of type FIl (lUPAC classification). This indicates the presence of fairly uniform mesopores. The texture characteristics of selected porous glass membranes are summarized in Tab. 1. The variable texture demanded the application of various characterization techniques and methods of evaluation. 

Fig. 1 Nitrogen sorption isotherms (77 K) of the parent MCM 41 and the postmodified MCM 41 materials (filled symbols denote desorption points).

Pyrolysis of the intrachaimel polyacrylonitrile led to the expected loss of nitrogen, similar to observations in bulk and thin film experiments. As in the case of polyaniline in MCM-41 (see above), nitrogen sorption isotherms showed reduced pore volumes for the inclusion compounds, demonstrating the formation of PAN and carbonized material in the chaimels of the host. 

DFT and molecular simulation methods have been applied to the analysis of adsorbents in two main capacities. For nonporous adsorbents, DFT can be used to provide a local isotherm r(P,e) in order to solve eq. (2) for the distribution of site energies on the adsorbent surface [1] A sample result is shown in Fig. 5 for the site energy distribution of a heterogeneous activated carbon obtained from DFT analysis of the nitrogen sorption isotherm. 

Nitrogen sorption isotherms at 77 K were calculated by means of the simulated 3D networks. Besides the Kelvin equation, necessary for determining the critical radius of curvature Rc, at which condensation and evaporation would occur, it is also necessary to consider specific menisci interactions and network effects that can influence the sorption phenomena [5, 7]. The existence of an adsorbed layer is indeed of great importance on the outcome of a sorption process, but for simplicity it will not be considered in this treatment. 

Figure 3. Nitrogen sorption isotherms of a calcined silica sample (open circles adsorption, open squares desorption), particle size 1.8 pm, template n-hexadecylamine.

In Figure 1 nitrogen sorption isotherms at 77 K for the pristine B and impregnated B-Fc203 MCM-48 silica materials are shown. Both sorption isotherms exhibit similar shape, i.e reversible pore condensation at p/po < 0.4. The MCM-48 silica phases exhibit no microporosity as revealed by measurements in the low pressure region [13]. Different methods were used to analyze the nitrogen sorption isotherms to obtain surface and pore size... 

Fig. 3.16 Nitrogen sorption isotherms at 77 K of silanised silica samples (p/po range from 0.5 to 1).

Broekhoff, J.C.P. and de Boer, J.H. (1967). Studies on pore systems in catalysis. IX. Calculation of pore distributions from the adsorption branch of nitrogen sorption isotherms in the case of open cylindrical pores. A. Fundamental equations. J. Catai, 9, 8-14. 

Broekhoff, J.C.P. and De Boer, J.H. (1968). Pore systems in catalysts. XII. Pore distributions from the desorption branch of a nitrogen sorption isotherm in the case of cylindrical pores. 1. An analysis of the capillary evaporation process. J. Catal, 10(4), 368-76. 

Nitrogen sorption isotherms were recorded at 77 K with a Micromeritics ASAP 2000 instrument after outgassing the samples at 423 K for 12 h under a pressure of 0.1 Pa. BET formalism was applied for determination of the specific surface area. Table 1 presents the surface area of the prepared catalysts. 

The textural characteristics were determined by X-ray diffraction and nitrogen sorption isotherm analysis. 

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