Physisorption pore volume measurement

The fresh and spent catalysts were characterized with the physisorption/chemisorption instrument Sorptometer 1900 (Carlo Erba instruments) in order to detect loss of surface area and pore volume. The specific surface area was calculated based on Dubinin-Radushkevich equation. Furthermore thermogravimetric analysis (TGA) of the fresh and used catalysts were performed with a Mettler Toledo TGA/SDTA 851e instrument in synthetic air. The mean particle size and the metal dispersion was measured with a Malvern 2600 particle size analyzer and Autochem 2910 apparatus (by a CO chemisorption technique), respectively. 

A low temperature nitrogen sorption was carried out on an automated physisorption instrument (ASAP 2000, Micromeritics Instrument Corporation). Before the measurement, the sample was degassed at 350 C for 4-5 h until the vacuum of system was better than 0.67 Pa. The data for micropore were obtained from t-plot, and those for mesopore and distribution of mesopore were calculated by BJH method (using desorption curve). The single point total pore volume at high relative pressure was taken as the total volume. 

Aqueous ammonium heptamolybdate (Alfa, (NH4)6Mo70244H20, 99.999%) solutions were prepared so that a metal loading of 6 wt % Mo would fill 80% of the available pore volume of the mesoporous synthetic clays. Following Mo impregnation and recalcination at 400°C for 5 hr, the pore volumes were measured again using an established LN2 physisorption... 

As evidenced by curves on figures 4 and 5, changes in texture characteristics are quasi-linearly related to increasing carbon content. It also appears that calculated surface areas strongly depend on the physisorption conditions, while measured adsorbate volumes are less affected. This observation is in favor of erroneous assumptions on nitrogen molecule area for the calculations of specific surface area [10]. But, as mentioned above, nitrogen molecule could penetrate in smaller pores, increasing measured micropore volume and surface areas. 

The process of ion exchange will affect the available pore volume inside the zeolite. The micropore volume has been measured by Na physisorption. The Na physisorption isotherms of the CuHis loaded zeolite samples are of Langmuir type I. The evolution of the micropore volume as a function of the initial copper concentration in the ion exchange solution is presented in Figure 4. The micropore volume decreases from 0.34 ml/g for a pure Y zeolite to 0.29 ml/g for the highest copper loading. The curve displays a bend in going from an initial copper concentration of 0.25 Cu/UC to an initial copper concentration of 0.50 Cu/UC. This phenomenon may be attributed to an increase in the relative amount of the more bulky complex B in the pore system of the zeolite. 

Nitrogen physisorption was performed with a Micromeritics ASAP 2400 apparatus. Measurements were done at -196°C. Prior to the measurements the powdered samples were degassed for 24 hours at 300°C in vacuum. Surface areas, pore volumes and pore size distributions were determined with standard BET and BJH theory. 

Their isotherms are classified as type IV with most of the pores in the mesopore region. Table 20.7 shows the structural parameters of these sono-aerogels as a function of temperature as determined from nitrogen adsorption data. The sample densities p were evaluated from the total pore volume per mass unit from Vp measured from the N2 physisorption experiments. The mean pore size is evaluated as 1 = AV ISbet- Table 20.7 shows that the... 

The specific surface area (BET) and pore volume were measured using a Micromeretics ASAP 2400. Prior to the physisorption experiment, the sample was outgassed in nitrogen at 250°C. 

In addition to the evaluation of the combined micro and mesoporous carbons, also siliceous materials were analyzed. More recently is there also a growing interest in the characterization of siliceous materials with CO2 adsorption and the application of the DR-equation [13]. The application of the DR-equation and the proposed correction on this material will provide fh er insight on the universal applicability of this approach. To this end the N2 and CO2 physisorption characteristics were measured on two purely mesoporous MCM-41 materials. The BJH pore size distribution (N2) of these mesoporous materials shows a narrow pore size distribution around 23 A and 32 A respectively. The corresponding specific surface area (5bet), total pore volume (FloiaO. and results fiom the DR-equation obtained by CO2 adsorption are given in Table 3. 

The surface area and the dimensions and volume of the pores can be determined in many ways. A convenient method is based on measurement of the capacity for adsorption. The experimental techniques do not differ from those used for chemisorption (see Section 3.6.3). The fundamental difference between physi.sorption and chemisorption is that in chemisorption chemical bonds are formed, and, as a consequence, the number of specific sites is measured, whereas in physisorption the bonds are weak so that non-chemical properties, in particular the surface area, are determined. 

CW-EPR X-band measurements were performed on a Bruker ESP 300E Spectrometer at a temperature of 120 K. The CuHis complexes are paramagnetic due to the S=l/2 spin of the Cu " ion. Nitrogen physisorption was performed with a Micromeritics ASAP 2400 apparatus. Measurements were done at 77 K. Prior to the measurements the zeolite samples were degassed for 24 hours at 373 K in vacuum. Micropore volumes and pore size distributions were determined with standard BET and BJH theory. Diffuse Reflectance Spectroscopy of the CuHis complex encapsulated zeolite samples were taken on a Varian Cary 5 UV-Vis-NIR spectrophotometer at room temperature. The DRS spectra were recorded against a halon white reflectance standard in... 

Nitrogen physisorption measurements were performed on a Micromeritics Tristar 3000 apparatus at -196 °C. Prior to analysis the samples were dried in a helium flow for 14 horns at 120 °C. Surface areas (St), and micropore (Vmicro) and mesopore (Vmeso) volumes were determined using the t-method [13] with the Harkins-Jura thickness equation. There is no standard method for the determination of blocked mesopore volume (Vmeso,bi)- For this we used the pore size distribution from the desorption branch of the isotherm calculated using BJH theory [14]. The total amoimt of Vmeso,bi was determined considering that the volume in pores with a diameter of 2 - 5 run is (partially) blocked. 

The catalyst and support surface areas, porous volumes and pore size distributions were measured by physisorption of N2 at -196°C on a Micromeritics ASAP 2000 instrument. Prior to measurement, samples were outgassed at 150°C under 0,13 Pa. Surface area, porous volume and pore size distribution values were computed, using BET and BJH equations, from the amount of N2 physisorbed at different relative pressure. 

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