Microporous materials solids

Karge FI G 1997 Post-synthesis modification of microporous materials by solid-state reactions Stud. Surf. Sol. Catal. 105 1901-48... 

Volume 104 Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid Surfaces edited by W. Rudzihski, W.A. Steele and G. Zgrablich Volume 105 Progress in Zeolite and Microporous Materials... 

Another recent new application of a microporous materials in oil refining is the use of zeolite beta as a solid acid system for paraffin alkylation [3]. This zeolite based catalyst, which is operated in a slurry phase reactor, also contains small amounts of Pt or Pd to facilitate catalyst regeneration. Although promising, this novel solid acid catalyst system, has not as yet been applied commercially. 

Adachi-Pagano, M., Forano, C. and Besse, J.-P. (2003) Journal of Materials Chemistry, 13, 1988-1993. de Roy, A., Forano, C., El Malki, M. and Besse, J.-P. (1992) Synthesis of Microporous Materials, inExpanded Clays and Other Microporous Solids... 

In 1992, Mobil reported a novel family of molecular sieves known as the M41S materials that established an entirely new area in nanoporous solids (168,169). The M41S materials expanded the range of pore sizes into the mesoporous domain (20-300 A). The impact of this discovery on molecular sieve research has been profound. In 1998, an international conference solely devoted to mesoporous molecular sieves was founded (170). The journal Microporous Materials even re-... 

Pores are found in many solids and the term porosity is often used quite arbitrarily to describe many different properties of such materials. Occasionally, it is used to indicate the mere presence of pores in a material, sometimes as a measure for the size of the pores, and often as a measure for the amount of pores present in a material. The latter is closest to its physical definition. The porosity of a material is defined as the ratio between the pore volume of a particle and its total volume (pore volume + volume of solid) [1]. A certain porosity is a common feature of most heterogeneous catalysts. The pores are either formed by voids between small aggregated particles (textural porosity) or they are intrinsic structural features of the materials (structural porosity). According to the IUPAC notation, porous materials are classified with respect to their sizes into three groups microporous, mesoporous, and macroporous materials [2], Microporous materials have pores with diameters < 2 nm, mesoporous materials have pore diameters between 2 and 50 nm, and macroporous materials have pore diameters > 50 nm. Nowadays, some authors use the term nanoporosity which, however, has no clear definition but is typically used in combination with nanotechnology and nanochemistry for materials with pore sizes in the nanometer range, i.e., 0.1 to 100 nm. Nanoporous could thus mean everything from microporous to macroporous. 

The combination of dyes with microporous materials opens-up a way to develop selective chemosensors microporous zeolites with an anchored squaraine 27 (Fig. 13) and some other types of dyes can be used as chemosensors for the chromogenic discrimination of amines [75], These dye-zeolite hosts are expected to be promising sensor materials allowing the visible discrimination of selected target guests by size and/or polarity within families or closely related molecules. It was found that the response of the solid to amines was basically governed by the three-dimensional architecture of the solid material. 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

J. Zhu, Z. Lin and Y. Huang, Zr and Mg solid-state NMR characterization of the local environments of the metal centers in microporous materials. Chem. Phys. Lett., 2008,461, 260-265. 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

The present paper is concerned with hydrogen storage in different crystalline solids. Such solids can be metal hydrides, carbon-based materials, and microporous materials. 

Structures originated by molecular self-assembly are usually larger (on the order of several nanometers, yielding mesoporous materials, Figure 3.4) than those obtained from organic templates (typically microporous, pore size <2nm) [5], The large size of the mesopore (2-50 nm) facilitates the access of reactants to the interior of the solid. This allows for processing of bulky molecules that cannot access the narrower porosity of microporous materials, like zeolites. Control of the synthesis... 

On the other hand, it is impossible to apply the SP method to the correct description of gas adsorption in the micropores, since the adsorption in the micropores does not occur by multilayer adsorption but by micropore volume filling process. In this case, the pore fractal dimension gives a physical importance for the description of structural heterogeneity of the microporous solids. Terzyk et al.143"149 have intensively investigated the pore fractal characteristics of the microporous materials using gas adsorption isotherms theoretically simulated. 

It forms a new microporous redox-solid acting as a reversible, high affinity and high capacity (>90 pmol g 1) dioxygen-sorbing material[3] and ranks among the best compared with [Con(bipyridine-terpyridine)] and [Con(CN)5]3"NaY.[115 116 117] On... 

The formation of an amorphous solid was first reported in 1935 [132,133]. These authors used the route of depositing warm water vapor on a cold substrate, which freezes in excess free energy by the rapid change in temperature. At substrate temperatures above 160K, the deposit was found to be crystalline ice I, whereas below this temperature, an amorphous solid was obtained. These deposits are referred to as ASW, which is a microporous material that can adsorb gases [134, 135]. In fact, ASW also condenses on interstellar dust particles and is likely the most abundant form of solid water in the universe. Therefore, studies on ASW bear an astrophysical relevance [134, 136]. The microporosity can be reduced greatly by sintering the sample to no more than 120 K. 

The problem of description of microporous materials is one of most complicated in the physical chemistry of solid state and interface. However, microporous materials have various applications in numerous fields, that is the reason for their large experimental and theoretical studies. 

According to second and third observations, it is difficult to appreciate the maximum value of the surface free energy and surface enthalpy of a solid, especially in the case of microporous materials which are widely efficient adsorption properties of the surface (sample V). Therefore, for this material, more works may be needed on the adsorption isotherm, spreading pressure, isosteric heat of adsorption, and even heterogeneities of solid surfaces. They are concerned with the finite concentration technique with increasing amount adsorbed, which will be dealt to some extent in the next section. 

In microporous materials where Knudsen diffusion prevails, De cannot be calculated by solving Fick s law. The use of a discrete particle simulation method such as dynamic MC is appropriate in such cases (Coppens and Malek, 2003 Zalc et al., 2003, 2004). In the Knudsen regime, relatively few gas molecules collide with each other compared with the number of collisions between molecules and pore walls. One of the fundamental assumptions of the Knudsen diffusion is that the direction in which a molecule rebounds from a pore wall is independent of the direction in which it approaches the wall, and is governed by the cosine law the probability d.v that a molecule leaves the surface in the solid angle dm forming an angle 0 with the normal to the surface is... 

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