Adsorption, measurement

Fig. XVn-6. Schematic of gravimetric apparatus for adsorption measurements. (From Ref. 30. Reprinted with permission from American Chemical Society, copyright 1995.)...

Nelsen F M and Eggertsen F T 1958 Determination of surfaoe area adsorption measurements by a oontinuous flow method Anal. Chem. 30 1387-90... 

Mercury porosimetry is generally regarded as the best method available for the routine determination of pore size in the macropore and upper mesopore range. The apparatus is relatively simple in principle (though not inexpensive) and the experimental procedure is less demanding than gas adsorption measurements, in either time or skill. Perhaps on account of the simplicity of the method there is some temptation to overlook the assumptions, often tacit, that are involved, and also the potential sources of error. 

In writing the present book our aim has been to give a critical exposition of the use of adsorption data for the evaluation of the surface area and the pore size distribution of finely divided and porous solids. The major part of the book is devoted to the Brunauer-Emmett-Teller (BET) method for the determination of specific surface, and the use of the Kelvin equation for the calculation of pore size distribution but due attention has also been given to other well known methods for the estimation of surface area from adsorption measurements, viz. those based on adsorption from solution, on heat of immersion, on chemisorption, and on the application of the Gibbs adsorption equation to gaseous adsorption. 

We therefore felt it timely to attempt a critical exposition and assessment of the common methods for the evaluation of the surface area and pore size distribution of solids from adsorption measurements. Our main concern has therefore been with the use of adsorption data for these purposes rather than with adsorption per se and it is for this reason that our treatment of theoretical matters, whilst sufficiently detailed to bring out the nature of the assumptions underlying the various methods, is not exhaustive we have not set out to write a text-book or a treatise on adsorption, and our choice of material from the literature has been dictated solely by its seeming suitability for the explanation or illustration of the topic under discussion. 

Deterrnination of the specific surface area can be made by a variety of adsorption measurements or by air-permeability deterrninations. It is customary to calculate average particle size from the values of specific surface by making assumptions regarding particle size distribution and particle shape, ie, assume it is spherical. 

Surface Area Determination The surface-to-volume ratio is an important powder property since it governs the rate at which a powder interacts with its surroundings. Surface area may be determined from size-distribution data or measured directly by flow through a powder bed or the adsorption of gas molecules on the powder surface. Other methods such as gas diffusion, dye adsorption from solution, and heats of adsorption have also been used. It is emphasized that a powder does not have a unique surface, unless the surface is considered to be absolutely smooth, and the magnitude of the measured surface depends upon the level of scrutiny (e.g., the smaller the gas molecules used for gas adsorption measurement the larger the measured surface). 

Adsorption Measurements during Surface Catalysis Kenzi Tamaru... 

The authors thank Kevin Ewsuk, Chris DiAntonio, Terry Garino, Dale Zschiesche and Denise Bencoe of Sandia National Laboratories for fabricating the ceramics and performing the N2 adsorption measurements.a. F.M. and D. O. K. thank Dr. Doug Smith of Nanopore Inc. for fabrication of the fumed silica samples, and S. D. B. thanks Dr. Eiichi Fukushima of New Mexico Resonance and Dr. Mark... 

The amount of a certain element which can be detected by XPS depends mainly on the specific scattering cross section. These cross sections are tabulated [15, 22] relative to either C or Na and vary between 0.5 for B and 22.9 for Cs with C as unity. An easy method for sensitivity determinations of the overall system are adsorption measurements. The amount of the adsorbate can be adjusted either electrochemically (UPD of... 

Fig. 1.2. Flow cell for adsorption measurements and on-line mass spectroscopy. The working electrode (w.e.) at the bottom of the cell is conneced directly to the MS c.e. = counter electrode, r.e. = reference electrode.

The pros and cons of oxidative dehydrogenation for alkene synthesis using doped cerianites as solid oxygen carriers are studied. The hydrogen oxidation properties of a set of ten doped cerianite catalysts (Ce0.9X0.1Oy, where X = Bi, In, La, Mo, Pb, Sn, V, W, Y, and Zr) are examined under cyclic redox conditions. X-ray diffraction, X-ray photoelectron spectroscopy, adsorption measurements, and temperature programmed reduction are used to try and clarify structure-activity relationships and the different dopant effects. 

The authors would like to acknowledge the contributions of the following researchers J.R. DeBaun and L.S. Mullen-Rokita, for helpful discussions E.B. Cramer, for assisting with the adsorption measurements L.-S. Yu-Farina, for the water solubility and partition coefficient measurements H. Myers, for the vapor pressure measurements and R.R. Winter, for running the MACCS molecular structure analyses. 

Results and Discussion on Dynamic Adsorption Measurements. Baker dolomite was used to study the dynamic adsorption experiment. The computed porosity of the rock was 24%. One concentration below the CMC of AEGS, one at CMC, and two concentrations above CMC were chosen to measure the adsorption of this surfactant with Baker dolomite. The mass of surfactant adsorbed per gram of rock is plotted as a function of flow rate in a semi-log plot in Figure 9. 

The work reported here is a part of a larger project entitled Improvement of C02 Flood Performance, which has been supported by the US Department of Energy, the New Mexico Research and Development Institute, and a Consortium of oil companies. We extend them our great appreciation. Acknowledgement is also made of the efforts of Mustofa Sadeq for collecting the data for adsorption measurements and James McLemore for his assistance in the experimental parts. 

The total pore volume can also be determined from adsorption measurements if one knows the volume of vapor adsorbed under saturation conditions. For high surface area catalysts the amount of material adsorbed on particle exteriors will be negligible compared to that condensed in the pores. Hence the liquid phase volume equivalent to the amount of gas adsorbed is equal to the pore volume. The liquid density is assumed to be that corresponding to the saturation conditions in question. This technique is less accurate than that described previously. 

MCM-41 samples have been characterized by means of powder X-ray diffraction (X Pert Philips, CuKa radiation), nitrogen adsorption measurements at 77 K (Quantachrome Autosorbl) and Field Emission Scanning Electron Microscopy (Assing FESEM Supra 25) before soaking in SBF and after different immersion times. 

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. 

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

The results of chemical analysis show that all samples have similar values of Si/Al ratio and confirm that the recrystallization procedure doesn t lead to any significant changes in chemical composition. On the contrary, the adsorption measurements point to remarkable changes in zeolite texture (Fig.l). 

Poirier, E., R. Chahine, P. Benard, G. Dorval-Douville, L. Lafi, P.A. Chandonia, Hydrogen adsorption measurements and modeling on metal-organic frameworks and single-walled carbon nanotubes. Langmuir 22(21), 8784-8789, 2006. 

Ellipsometry. Adsorption measurements were performed with a Shimadzu P-10 Type ellipsometer at 25 °C. The light source was a Nihon Denchi SH-85 Type high pressure mercury lamp. The wavelength of the incident light was 546 nm and incident angle was 70 0. ... 

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