Mercury porosimetry isotherms

Porosimetry isotherms, corresponding to condensation and evaporation, have been constructed " by conversion of the hydraulic pressure to the corresponding relative pressure using equation (12.27). A typical isotherm from mercury intrusion-extrusion data (Fig. 12.4) is shown in Fig. 12.5 for an alumina sample. 

Following the convention in gas adsorption-desorption isotherms, the mercury isotherm, illustrated in Fig. 12.5, is plotted as volume versus relative pressure so that the radius increases from left to right. Curve I in Fig. 12.5 represents the condensation isotherm from the extrusion curve and curve II is the evaporation isotherm from the intrusion data. Since no adsorption takes place on the pore walls prior to the filling of pores in mercury porosimetry as occurs in gas adsorption, the usual knee of the isotherm is absent. However, condensation-evaporation isotherms from mercury porosimetry are strikingly similar to adsorption-desorption... 

For the detailed study of reaction-transport interactions in the porous catalytic layer, the spatially 3D model computer-reconstructed washcoat section can be employed (Koci et al., 2006, 2007a). The structure of porous catalyst support is controlled in the course of washcoat preparation on two levels (i) the level of macropores, influenced by mixing of wet supporting material particles with different sizes followed by specific thermal treatment and (ii) the level of meso-/ micropores, determined by the internal nanostructure of the used materials (e.g. alumina, zeolites) and sizes of noble metal crystallites. Information about the porous structure (pore size distribution, typical sizes of particles, etc.) on the micro- and nanoscale levels can be obtained from scanning electron microscopy (SEM), transmission electron microscopy ( ), or other high-resolution imaging techniques in combination with mercury porosimetry and BET adsorption isotherm data. This information can be used in computer reconstruction of porous catalytic medium. In the reconstructed catalyst, transport (diffusion, permeation, heat conduction) and combined reaction-transport processes can be simulated on detailed level (Kosek et al., 2005). 

The new composite (SC-155) and some of its precursors and derivatives were characterized by LOI (loss on ignition), XRD ( X ray diffraction), 1R (infrared spectra), BET specific surface area, nitrogen adsorption desorption isotherms, pore size distribution (mercury porosimetry), dynamic methylene blue adsorption and SEM (Scanning Electron... 

Nitrogen adsorption/condensation is used for the determination of specific surface areas (relative pressure < 0.3) and pore size distributions in the pore size range of 1 to 100 nm (relative pressure > 0.3). As with mercury porosimetry, surface area and PSD information are obtained from the same instrument. Typically, the desorption branch of the isotherm is used (which corresponds to the porosimetry intrusion curve). However, if the isotherm does not plateau at high relative pressure, the calculated PSD will be in error. For PSD s, nitrogen condensation suffers from many of the same disadvantages as porosimetry such as network/percolation effects and pore shape effects. In addition, adsorption/condensation analysis can be quite time consuming with analysis times greater than 1 day for PSD s with reasonable resolution. 

Two epoxy-activated related supports, Sepabeads EC-EP3 and EC-EP5 (Figure 11.3), were assayed for the immobilization of A. aculeatus fructosyltransferase. By combination of nitrogen isotherms and mercury porosimetry analyses, the textural properties of both carriers were determined (Table 11.3). As shown, both samples... 

Gas adsorption Is most widely used to assess porosity, especially by analyzing the hysteresis loops appearing in the isotherms due to capillary condensation in pores (fig. 1.13 types IV and V). However, there are a number of alternatives. Including mercury porosimetry, neutron and X-ray scattering. 

For description of textural properties of carbonaceous adsorbents, adsorption/desorption isotherms of vapours and gases in static conditions as well as mercury porosimetry are used. The latter method often leads to destruction of porous structure of investigated materials while the usage of the former one is affected by the specific properties of molecular sieves described above. Taking into account these limitations, in this work the authors have made an attempt of determination of porous structure of carbon molecular sieves with the used of the pycnometric technique. 

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. 

The mercury porosimetry intrusion plot of a mesoporous glass membrane is given in Fig. 2. That curve and the isotherm shapes in Fig. 1 are indicators for a relatively narrow pore size distribution of the ultrathin porous glass membranes. 

Textural characterisation of the samples was carried out by measuring apparent density (mercury at 0.1 MPa), mercury porosimetry and N2 and CO2 adsorption isotherms, at -196 and 0 °C, respectively. The apparent surface areas of the samples were obtained by using the BET equation [5]. The micropore size analysis was performed by means of the t-plot and the Dubinin-Astakhov methods [6]. 

The pore size distribution (see Fig. 3) can be obtained from the mercury porosimetry data and the t-plot from N2 adsorption isotherms, using an active carbon with a very low surface area as a reference [13]. It was observed that the volumes of mercury intruded were very small. As a consequence, the volumes of meso (the largest ones) and macropores are low. Thus, the samples studied are mainly microporous, as already mentioned in the N2 and CO2 adsorption isotherm results. 

We will provide a succinct introduction to the main textural characterisation techniques for catalysts. As a heterogeneous catalyst comprises a support and an active phase, we will distinguish between techniques intended for studying the support, which will be presented in a first section (Physisorption isotherms and mercury porosimetry) and techniques used to characterise the active phase, in the strict sense of the term, shown in a second section (Chemical adsorption). For each technique, we will show the theoretical principle, the way in which the measurement is carried out and the equipment used. Finally, examples will be used to illustrate the type of response that can be given using these characterisation techniques. 

For macroporous samples (pore size greater than 50 nm), the absence of any capillary condensation phenomenon means that only the specific surface area can be obtained from the adsorption isotherm using the BET equation. Mercury porosimetry (Paragr. 1.2) will then be necessary to obtain the pore size distribution. 

The bulk densities were calculated from weight and volume measurements. Skeletal densities were measured by He pycnometry N2 adsorption-desorption isotherms were determined at 77 K on a Carlo Erba Sorptomatic 1900 and their analysis was done using a set of well-known techniques [5], Mercury porosimetry up to a pressure of 200 MPa is performed on a Carlo Erba Porosimeter 2000. Samples were examined using a transmission electron microscope to obtain particle and aggregate sizes [2]. 

The spectrum of pore dimensions. Pores of radius 10-300 A. are studied by analyzing, according to the C. Pierce method, the nitrogen desorption isotherms at the temperature of liquid nitrogen 21). For pores of radius between 300 A. and 6m, the mercury porosimetry under high pressure 22, 23) is used. 

In gas adsorption for micro-, meso- and macropores, the pores are characterized by adsorbing gas, such as nitrogen at liquid-nitrogen temperature. This method is used for pores in the ranges of approximately <2 nm micropores), 2 to 50 nm (mesopores), and >50 nm macropores) (ISO/FDIS 15901-2, Pore Size Distribution and Porosity of Solid Materials—Evaluation by Mercury Porosimetry and Gas Adsorption, Part 2 Analysis of Meso-pores and Macro-pores by Gas Adsorption ISO/FDIS 15901-3, Part 3 Analysis of Micro-pores by Gas Adsorption). An isotherm is generated of the amount of gas adsorbed versus gas pressure, and the amount of gas required to form a monolayer is determined. 

The aim of this work is to explore the applicability of the sol-gel method for the preparation of Ag/Si02 and Cu/Si02 catalysts and to see whether such a method can yield silver and copper species stabilized by the carrier. Characterization of the catalyst structure by several physical and chemical techniques, including N2 adsorption-desorption isotherms, mercury porosimetry measurements, X-ray diffraction and transmission electron microscopy, has been used to correlate the microstructure of Ag/Si02 and Cu/Si02 catalysts with their catalytic performance. 

N2 adsorption-desorption isotherms were determined at 77 K after outgassing for 24 h at room temperature. The mercury porosimetry measurements were performed between 0.01 and 200 MPa after outgassing the sample monolith for 2 h at ambient temperature. The size of silica and metallic particles was examined by transmission electron microax)py (TEM). The composition and size of the metallic particles were examined by X-ray diffraction (XRD). 

Many characterization techniques developed for the characterization of meso-porous and microporous materials have been adapted to membrane characterization (e.g., mercury porosimetry, adsorption and desorption isotherms, and thermoporometry). These techniques are related to morphological parameters... 

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