Nitrogen physisorption methods

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. 

The catalysts studied were characterized using X-ray powder diffraction (XRD), X-ray fluorescence analysis (XFA), transmission electron microscopy (TEM), X-ray adsorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and hquid nitrogen physisorption methods. 

The catalysts studied were characterized using XFA, TEM, XANES, EXAFS, XPS, and liquid nitrogen physisorption methods. The total organic caibon was detected by standard methodology of chemical oxygen demand (COD). 

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]. 

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... 

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 ... 

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

Specific surface areas of the synthesized Ti02-Al203 samples was estimated by nitrogen physisorption at 77 K using the BET method. 

The specific surface area and pore volume distribution were obtained with nitrogen physisorption using BET method in a Micromeritics ASAP 2000. 

BET surface area and microporous volume determination. Surface area measurements were performed by nitrogen physisorption at 77 K using the static volumetric apparatus (Micromeritics ASAP 2000 adsorption analyzer) with application of the BET method. All measurements were performed after treatment of solids under vacuum at 110 °C. 

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. 

A dip coating method is applied in order to allow the deposition of Pd/y-AlaOa on FeCrAlloy-type fibers. All samples are investigated by means of XRD, XPS, CO chemisorption and nitrogen physisorption. The catalytic fibers are tested in the total combustion of methane showing that O2/H2 gaseous pretreatment, which takes place before the catalytic reaction, is strongly beneficial as confirmed by a better dispersion of Pd particles. 

Using three different preparation methods copper oxide modified MCM-41 silica and Al-MCM-41 materials were obtained and characterized by various techniques (nitrogen physisorption, XRD and TPR-TGA) and methanol decomposition as a catalytic test reaction. At certain conditions of impregnation and drying at room temperature and under vacuum it was possible to form highly dispersed CuO nanoparticles incorporated almost exclusively within the mesoporous host structure. These particles could be reduced with H2 at considerably lower temperatures than the bulk CuO. 

The surface area of the catalysts was measured by conventional BET methods (nitrogen physisorption at -196°C using a Quanta Chrome-NOVA 1000 instrument). The actual metal loading was measured by inductively-coupled plasma / optical emission spectroscopy (ICP/OES). The acidity and basicity of the synthesized catalysts were measured by NHj and COj thermoprogrammed desorption, respectively, using an AMI-100 (Zeton-Altamira, Pittsburgh, PA) characterization system. The catalyst samples were reduced in 10% H /Ar at 450°C for 8 hours, followed by treatment in 10% NH,/He or 10% COj/He at 35°C and then by desorption up to 400°C with a heating rate of 10°C/min. 

Nitrogen physisorption can give information about the surface area and pore-size distribution of samples fluorinated at 25 °C for two hours. The pore size distribution is obtained through the Barrett-Joyner-Halenda (BJH) method using the adsorption branch [34]. No change in the isotherm type is observed after fluorination, proving that the mesopore system is conserved. Eluorination of a pristine silica with Sbet = 508 m g ... 

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. 

In principle, the as-method is not restricted to nitrogen adsorption and can be applied to any gas-solid physisorption system irrespective of the shape of its isotherm it can be used to check the validity of the BET area and also to identify the individual mechanisms (monolayer-multilayer adsorption, micropore filling or capillary condensation). Numerous examples of different as-plots are to be found in subsequent chapters. Here, we are concerned with the general principles of the as-method of isotherm analysis with particular reference to the evaluation of surface area. The distinctive features of various hypothetical as-plots are revealed in Figure... 

Among the molecule or ion adsorption methods, gas adsorption is the most important one. It uses a reversible van der Waals adsorption or physisorption. A gas molecule adsorbed on the sample surface occupies a specific space. For example, the nitrogen molecule N2 requires a surface area of 16.2x 10 m. If one assumes that the entire surface of a powder sample, including those pores that are accessible to the molecules, is covered with a monomolecular layer of the adsorbate, the surface can be calculated from the number of adsorbed molecules and their space requirement. Measurements of the adsorbed amount of gas can be accomplished either volumetrically or gravimetrically and by means of carrier gas or radioactive methods. 

Surface Measurement The specific surface of a porous solid material can be determined from the adsorbed amount of an adsorptive when its surface demand is known. The most reliable method for doing this is based upon the physisorption of gases (mostly nitrogen) near their boiling points. The so-called BET isotherm is used for the analysis. This isotherm developed in 1938 by Bnmauer, Emmet, and Teller takes multilayer adsorption into account as well. 

The physico-chemical properties of the solids were studied by different techniques. Nitrogen adsorption-desorption isotherms were measured at 77 K on a Micromeritics ASAP-2000 physisorption analyzer. Sbet was determined according to the BET equation, whereas the pore size distribution in the mesopore region was obtained applying the BJH method to the desorption branch of the isotherms. Vp was estimated from the nitrogen adsorption at P/Pq = 0.99. X-ray diffraction analyses (XRD) were... 

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