INDEX pore structure

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

The chemistry of Scheme 2 produces a cubic pore structure with long-range periodicity and unit cell parameter (Ko) of 8.4 nm. The material show a relatively large number of Bragg peaks in the X-ray diffraction (XRD) pattern, which can be indexed as (211), (220), (321), (400), (420), (332), (422), (431), (611), and (543) Bragg diffraction peaks of the body-centered cubic Ia-3d symmetry (Fig. 1). 

Six common isotherm shapes are shown in Figure 14.4. In fact, those are the classic isotherm types suggested by Brunauer et al. (1940). Each can be represented by numerous empirical equations, some of which are discussed later. The inherent shapes or types arise from the pore structure of the adsorbent, the nature of the forces between the adsorbent surface and adsorbate, and the dependence on concentration. Besides isotherms, other properties are related to adsorption capacity, especially surface area and pore size distribution. Some other properties are application oriented, such as CTC (carbon tetrachloride) index, iodine number, methylene blue factor, and molasses number, all defined in Table 14.1. They are frequently employed to describe activated carbons. 

Porous silicon materials are described as a mixture of air, silicon, and, in some cases, silicon dioxide. The optical properties of a porous silicon layer are determined by the thickness, porosity, refractive index, and the shape and size of pores and are obtained from both experimental- and model-based approaches. Porous silicon is a very attractive material for refractive index fabrication because of the ease in changing its refractive index. Many studies have been made on one- and two-dimensional refractive index lattice structures. The refractive index is a complex function of wavelength, i.e., n(X) = n(X) — ik(k), where k is the extinction coefficient and determines how light waves propagate inside a material (Jackson 1975). The square of the refractive index is the dielectric function e(co) = n(co), which contributes to Maxwell s equations. 

The specific surface area and pore structure are the most basic macroscopic physical properties of solid catalysts. Pore and surface are the reactive rooms of heterogeneous catalytic reactions, and the amount of surface area directly influences the level of catalytic activity. If the surface properties of catalyst are uniform, then their activity is directly proportional to their surface area. Catalytic reactions are generally influenced by the diffusion under industrial conditions, and the activity, selectivity and lifetime and almost all properties of catalyst are related to these two macroscopic physical properties. Although the activity for most catalysts is not proportional to their surface area, the surface area is still a visual physical quantity to evaluate catalyst performance, and sometimes acts as a control index of preparation. 

Porosity measurements include conventional techniques to assess pore volume and pore size distribution of mainly bulk gel samples. Although several physical properties, e.g. refractive index, show simple dependence on averaged porosity of the sample, it will become increasingly important to analyze the local pore structure of thin or small amount of samples. In the near future, the three-dimensional imaging with HR-TEM observation will become an important tool for researchers dealing with porous gels. 

Throughout hydration time, products are forming which progressively fill capillary pores. As a result, both total pore volume and critical pore radius of the microstructure decrease. Figure 9.16 shows the pore structure development of a cement paste from 1 to 28 days of hydration. MIP results show the rapid decrease in the total pore volume over the first 14 days of hydration, after which it decreases much more slowly. Both threshold and critical pore radii shift towards smaller sizes but stabilise beyond 14 days of hydration. The stabilisation of the critical pore entry size at about 7 nm might be explained by the increase in the saturation index for growth in the pore (Berodier and Scrivener 2015 Bizzozero et al. 2014 Steiger 2005). 

The synthesized Ti-MCM-41 sample shows a typical XRD pattern, similar to that reported in literature.[9] The pore diameter is about 35 A and the peaks can be indexed on a hexagonal structure. 

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