Pore micropores

Lewis D W, Sankar G, Wyles J K, Thomas J M, Catlow C R A and Willock D J 1997 Synthesis of a small-pore microporous material using a computationally designed template Angew. Chem. Int. Ed. Engl. 36 2675-7... 

Principal Adsorbent Types. Commercially useful adsorbents can be classified by the nature of their stmcture (amorphous or crystalline), by the sizes of their pores (micropores, mesopores, and macropores), by the nature of their surfaces (polar, nonpolar, or intermediate), or by their chemical composition. AH of these characteristics are important in the selection of the best adsorbent for any particular appHcation. 

Pore System Micro + Secondary Pores Micro + Secondary Pores Micropores... 

Different theoretical models applied to this pore size distribution can give relatively large variations of the calculated effective diffusivity value (DelT). The most commonly used approximations are (i) random-pore model (Wakao and Smith, 1962) using two characteristic transport pores (micropores ji and macropores M)... 

The support has an internal pore structure (i.e., pore volume and pore size distribution) that facilitates transport of reactants (products) into (out of) the particle. Low pore volume and small pores limit the accessibility of the internal surface because of increased diffusion resistance. Diffusion of products outward also is decreased, and this may cause product degradation or catalyst fouling within the catalyst particle. As discussed in Sec. 7, the effectiveness factor Tj is the ratio of the actual reaction rate to the rate in the absence of any diffusion limitations. When the rate of reaction greatly exceeds the rate of diffusion, the effectiveness factor is low and the internal volume of the catalyst pellet is not utilized for catalysis. In such cases, expensive catalytic metals are best placed as a shell around the pellet. The rate of diffusion may be increased by optimizing the pore structure to provide larger pores (or macropores) that transport the reactants (products) into (out of) the pellet and smaller pores (micropores) that provide the internal surface area needed for effective catalyst dispersion. Micropores typically have volume-averaged diameters of 50 to... 

V. Skeletal Isomerization of n-Butenes Catalyzed by Medium-Pore Microporous Molecular Sieves... 

Cracking of n- octane/2,2,4- trimethylpentane Al-M A reaction usefixl for discriminating between larger pore microporous materials based on reactants selectivity ratio. 46... 

According to the porosity data of Uchida et al. [102] the matrix of carbon grains (20-40 nm) forms an agglomerated structure with a bimodal psd. Primary pores (micropores, 5-40 nm) exist within agglomerates, between the carbon grains. Larger, secondary pores (macropores, 40-200 nm) form the pore spaces between agglomerates. The relation between the relative pore volume fractions of the two pore types depends on the contents of PFSI and PTFE. Due to their molecular size these components are not able to penetrate micropores. They affect only the macropore volume. The experimental study revealed that an increased PFSI content leads to a decrease of the macropore volume fraction. The opposite effect was found for PTFE. 

D channels. The structures of large-pore microporous materials share the following common features ... 

Assembly of Chiral Catalytic Centers in the Pores (Microporous and Mesoporous) of Molecular Sieves... 

D.W. Lewis, G. Sankar, J.K. Wyles, J.M. Thomas, C.R.A. Catlow, and D.J. Willock, Synthesis of a Small-pore Microporous Material using a Computationally Designed Template. Angew. Chem., Int. Ed. Engl., 1997, 36, 2615-2611. 

The magnitudes of gas diffusivities by different mechanisms follow the order meso-macropore gas diffusivity (Dp) > surface diffusivity (D ) in those pores > micropore diffusivity (Dm). For example. Dp... 

The Random-pore Model This model was originally developed for pellets containing a bidisperse pore system, such as the alumina described in Chap. 8 (Table 8-5 and Fig. 8-10). It is supposed that the pellet consists of an assembly of small particles. When the particles themselves contain pores (micropores), there exists both a macro and a micro void-volume distribu-... 

We must keep in mind that the pore volume of a gel generally consists of three families of pores micropores, mesopores, and macropores. If a straightforward relation between capillary forces and the pore size is applied, the highest stresses should be associated with the micropores. However, it is not clear that failure appears at this particular location. Macroscopic stresses may induce failure near macropores, where the mechanical strength of the network is low. During drying the largest pore size empties first. 

ACs are the most commonly used form of porous carbons for a long time. Typically, they refer to coal and petroleum pitch as well as coconut sheUs-based AC. In most cases, ACs are processed to be filled with rich micropores that increase the surface area available for gas sorption and separation. For this category, to get a definite classification on the basis of pore structure is difficult due to their countless products as well as their complex pore features. Based on the physical characteristics, they can be widely classified into the following types powdered, granular, extruded, bead ACs, etc. For the pore structure of ACs, actually, all the three types of pores (micropore, mesopore, and macropore) are included in one product (Fig. 2.1), with a wide pore size distribution [1, 2]. Up to now, many kinds of ACs have been well commercialized in gas sorption/separation including CO2 capture. For example, the BPL type with specific area of 1,141 m g is able to adsorb 7 mmol g CO2 under the conditions of 25 °C and 35 bar, while under the same conditions MAXSORB-activated carbon with specific area of 3,250 g can capture up to 25 mmol g [3]. 

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