Nitrogen adsorption and desorption

Fig. XVII-5. Schematic detector response in a determination of nitrogen adsorption and desorption. A flow of He and N2 is passed through the sample until the detector reading is constant the sample is then cooled in a liquid nitrogen bath. For desorption, the bath is removed. (From Ref. 28. Reprinted with permission from John Wiley Sons, copyright 1995.)...

Figure 1.6 Top Low-temperature nitrogen adsorption ( ) and desorption (x) isotherms measured on a calcined SBA-15 mesoporous silica solid prepared using an EO20PO70EO20 block copolymer [54]. Bottom Pore size distribution derived from the adsorption isotherm reported at the top [54]. A high surface area (850 m2/g), a uniform distribution of cylindrical nanopores (diameter —90 A), and a large pore volume (1.17 cm3/g) were all estimated from these data. These properties make this material suitable for use as support in the preparation of high-surface-area solid catalysts. (Reproduced with permission from The American Chemical Society.)...

One of the most widely used methods for determining the pore size and surface area of zeolites is nitrogen physisorphon. From the shape of the nitrogen adsorption and desorption isotherm the presence and shape of the mesopores can be deduced. As shown in Figure 4.41 a faujasite without mesopores have a type I isotherm since the micropores fiU and empty reversibly, while the presence of mesopores results in a combination of type I and IV isotherms. The existence of a hysteresis loop in the isotherms indicates the presence of mesopores while the shape of this hysteresis loop is related to their geometric shape. 

Nitrogen adsorption and desorption isotherms were performed at 77 K on a Micromeritics ASAP 2400 volumetric adsorption system. The pore size distribution and surface area were deduced from the adsorption isotherms using the BJH method and the BET equation. 

Figure 2. Nitrogen adsorption ( ) and desorption (O) isotherms of MSU-1 and -4 Silica obtained with Tergitol 15S12 and Tween 20. Nitrogen adsorption isotherms were measured at 77 K on a Micromeretics 2010 Sorptometer using standard continuous procedures and samples degased at 150°C for 15 hours.

Figure 4. Nitrogen adsorption and desorption isotherm curves and pore size distribution curve (inset) from the adsorption branch of (a) calcined mesoporous silica sphere and (b) calcined mesoporous alumina sphere.

Nitrogen adsorption and desorption isotherms of all the MTS samples exhibit type IV behavior showing reversible step at around p/po 0.3-0.4 typical for the filling of a regular mesoporous system (Figure 1). 

FIGURE 4 Nitrogen adsorption and desorption isotherms at 78 K. Pore size distributions in the micropore range are calculated from the isotherms using the Kelvin equation. 

In the present work we examine the microporosity of a TSLS complex formed from synthetic imogolite and natural montmorillonite. Nitrogen adsorption and desorption isotherms are reported and analyzed in terms of microporous volume and surface area. Also, the adsorption isotherm for an organic adsorbate, m-xylene, is reported. Preliminary FTIR results for the chemisorption of pyridine and catalytic studies of the dealkylation of cumene suggest that TSLS complexes are promising microporous acids for shape selective chemical conversions. 

Micropore Size Distribution Analysis. Low pressure nitrogen adsorption and desorption of fresh and coked catalysts were carried out using an Omicron Technology Omnisorp lOOCX. The data for the adsorption isotherms were collected at very low partial pressures of nitrogen (P/Pq < 10 ) to determine the BET surface area and the micropore volume. The micropore volume was estimated from the t-plots. The desorption isotherm was obtained to measure meso and macro pore volume which correspond to the pore volume larger than pore radius of Inm. 

In designing an adsorption column, the characterization of adsorbents should be done prior to experiments. In particular, one should know not only the specific area but also the pore size distribution of the adsorbent in order to confirm that it would be proper for a given purpose. Nitrogen adsorption and desorption isotherms, BET surface areas, and BJH (Barrett, Joyner and Halenda) pore size distributions of the synthesized sorbents... 

Figure 1 presents the nitrogen adsorption and desorption isotherms with BJH pore size distribution curves for MCM-48. The isotherms are type IV according to the lUPAC... 

Experimental conditions as in Table IV As measured by nitrogen adsorption and desorption. from Xu el al (57). 

The chemical compositions of the samples were determined by atomic adsorption spectroscopy (AAS). X-ray powder diffraction patterns were recorded after synthesis and template removal on a Siemens D5000 diffractometer using CuKa radiation. After calcination, nitrogen adsorption and desorption isotherms were measured on a Micromeritics ASAP 2010 sorption analyzer. Al MAS NMR spectra were recorded on a Bruker MSL 400 spectrometer using single pulse excitation with standard 4 mm rotors The resonance frequency was (Oo/271 = 104.31 MHz for Al using a 7t/20 pulse and a 0.5 s recycle delay. A 0.1 M solution of aluminum nitrate in water was employed as the chemical shift reference... 

Figure 1. Nitrogen adsorption and desorption Isotherms for polyphenylene oxide (PPO) membranes. (PPO-9 and PPO-10 Indicate the polymer concentration (wt. %) in the casting solution).

Figure 5. Hysteresis regions of nitrogen adsorption and desorption isotherms calculated for regular packings of spheres with uniform radii of 500 X. Total pore volume, Vj, given for each packing.

Chemical analysis showed that (Al+M)/ PO4 ratios in all the samples are nearly 1.0/0.95, which are due to incomplete precipitation of phosphates[15]. XRD patterns of all the samples showed amorphous character within 600°C calcination, which converted to crystalline at 800°C calcination[15]. The BET surface area, average pore diameter and pore volumes calculated from nitrogen adsorption and desorption isotherms are presented in Tablel. 

Figure 1. (a) Nitrogen adsorption and desorption isotherm of Pt/C. Solid symbol adsorption branch. Open symbol desorption branch, (b) Pore size distribution of Pt/C. 

Figure 14. Isotherm of nitrogen adsorption and desorption (left side) and pore-size distribution functions of sample A5 (right side).

Figure 11.11 (a) Nitrogen adsorption and desorption isotherms of calcined silica prepared... 

Nitrogen adsorption and desorption isotherms for the sludge adsorbent were measured using the standard N2-BET test (Micromeritics Instrument Corporation ASAP2000). The properties of the sludge adsorbents were also characterized by the BET surface area method. The surface fractal dimension D was calculated from their nitrogen isotherms using both the fiactal isotherm equations derived from the FHH theory. 

Nitrogen adsorption and desorption were measured at 77K with an automatic Carlo Erba Sorptomatic 1800 adsorptiometer. The samples were pretreated at 573K under vacuum (1.33 Pa). 

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