Textural properties of catalysts

Cylindrical pellets of four industrial and laboratory prepared catalysts with mono- and bidisperse pore structure were tested. Selected pellets have different pore-size distribution with most frequent pore radii (rmax) in the range 8 - 2500 nm. Their textural properties were determined by mercury porosimetry and helium pycnometry (AutoPore III, AccuPyc 1330, Micromeritics, USA). Description, textural properties of catalysts pellets, diameters of (equivalent) spheres, 2R, (with the same volume to geometric surface ratio) and column void fractions, a, (calculated from the column volume and volume of packed pellets) are summarized in Table 1. Cylindrical brass pellets with the same height and diameter as porous catalysts were used as nonporous packing. 

The study of the textural properties of catalyst supports is of primary importance in terms of understanding the catalytic phenomena involved in petrochemical and refining industry processes. In fact, characteristics, such as the specific surface area, pore size or total porous volume will be useful in various stages of a catalyst s existence its preparation (deposition of active phases), its use in catalysis and its regeneration. They directly influence the physicochemical properties of the solid as well as surface reactivity, shape selectivity and hydrodynamic properties. 

For FTS process, two main mesoscale phenomena can be summarized (1) the interaction between internal diffusion and external diffusion, which is determined by the texture properties of catalyst and flow type of reactor. Generally, the texture properties, such as the size and morphology of catalyst pellet, always influence the flow type of reactor. Therefore, those should be combined to discuss their effects on FTS reaction (Kim et al., 1989 Lee et al., 2004 Mikkola et al., 2007 Schneider and Mitschka, 1966). (2) The relationship between internal difiusion and the intrinsic properties of active site, which is influenced by texture properties and active phase of catalyst. As well known, texture properties and active phase of catalyst always influence each other, such as the catalyst with low-surface area is always difficult to form highly dispersed active metal particle. The above mesoscale phenomenon significantly affects on the deviation from the ASF distribution of FTS products. 

The physisorption of gases on solids is used for determining the textural properties of catalysts, such as surface area and pore size distribution. 

The composition and textural properties of fresh, spent, and regenerated catalysts is reported in Table 12.17. It can be first seen from this table that textural properties of catalyst are considerably reduced as frequently reported by others who have carried out heavy oil hydroprocessing tests ( 50% reduction). 

Table 1 gives the textural properties of the support and catalyst samples. As expected the pore volumes and the surface areas of the catalysts are lower than those of the support. This indicates that the palladium blocks some part of the... 

Table 1. Elemental analysis and textural properties of the MCM-22 catalysts.

Adapted from Guidotti et al. (189). Reaction conditions catalyst, 50 mg substrate, 1 mmol TBHP terpene (mol) =1 1 solvent, CH3CN Vtot mix., 10 mL temperature, 363 K time, 24 h magnetic stirring (ca. 800 rpm). Textural properties of the catalysts (A-E) are given in Table XII. Structures of the substrates (1-6) are shown in Scheme 6. 

The trend was studied and verified, for instance, for reactions catalysed by transition metal, organo- and enzyme catalysts entrapped in ORMOSIL prepared by copolymerization of tetramethoxysilane (TMOS) and the modifying co-precursor methyltrimethoxysilane (MTMS). It has been correlated with the encapsulation itself but also with the structure of the sol-gel matrix, namely the hydrophobicity-lipophilicity balance (HLB) and the textural properties of the materials.9... 

We attempted to improve the eatalytic performanee, including stability, of the silica-immobilized Co-POM catalysts by using hydrothermally stable supports, specifically, the mesostructured silicates SBA-15 and MCF, both modified with amino groups by grafting 3-aminopropyltrietoxysilane [97], The physico-chemical properties of three representative NH2-X (X = xerogel, SBA-15 and MSF) supported Co-POM catalysts are given in Table 1. The textural properties of the initial, POM-free supports are shown for comparison. 

Another coke formed in a FCC unit is occluded or residual coke. In a commercial unit this coke corresponds to coke formed on catalyst porosity and its content depends on textural properties of the catalyst (pore volume and pore size distribution) and the stripping system capacity in the reaction section. Finally on the FCC catalyst rests some high-molecular weight of nonvaporized hydrocarbons. These molecules do not vaporize or react at the reactor conditions and accumulate in the catalyst pores like a soft carbonaceous residue with high hydrogen content. 

In summary, textural parameters that are essential for the catalysts performance were prepared from variable combinations of CTAB/NH4OH/ H20 in the presence of co-surfactants, i.e. acetone and the light alcohols (MeOH, EtOH, PrOH). The resuts indicate that the porous structure of the materials thus obtained are maintained along the distinct TEOS and CTAB concentration ratios, even with the influence of diverse co-surfactants. Then, the textural properties of the mesoporosus MSS, measured by N2 adsorption, indicate a reproducibility of the textural properties, i.e. pore volume, mean pore size distribution and total surface area (Figure 15.8). 

We consider first the textural properties of a typical wormhole Ti-HMS in comparison to well ordered hexagonal Ti-MCM-41 and Ti-SBA-3 analogs prepared by S+I and S+XT electrostatic assembly pathways. Table 1 provides the surface areas and pore volumes that characterize the framework mesoporosity (Vfr) and textural porosity (Vtx). The total mesoporosity (Vtotai) is the sum of these two values. Each mesostructure contains 2 mole % Ti and exhibits a HK pore size near 2.8 nm. The values in parenthesis in the table are for the corresponding pure silicas. Note the very high ratio of textural to framework mesoporosity for the HMS molecular sieves (Vtx/Vfr = 1.06) compared to the hexagonal molecular sieves (Vtx/Vfr = 0.03). As will be shown below, the textural porosity of HMS catalysts can improve catalytic activity by facilitating substrate transport to the active sites in the mesostructure framework. 

The chemical, physical and technical properties of catalysts and many other porous technical materials are to a very great degree determined by both their texture and their structure, but the analytical composition of the surface also plays a role. Modern surface analysis techniques, like auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) have revealed that in many cases the atomic composition of the surface of a solid material deviates strongly from the composition of the bulk material. 

The overall performance of a catalyst is known to depend not only on the inherent catalytic activity of the active phase but also on the textural properties of the solid. The ability to control the specific surface area and the pore size distribution during the synthesis of amorphous silica-aluminas has been described for both surfactant micelle templated syntheses (M41-S (1), FSM-16 (2), HMS (3), SBA (4), MSU (5), KIT-1 (6)) and cluster templated sol-gel syntheses (MSA (7), ERS-8 (8)). 

Phosphorus also modifies the textural properties of the M0S2 slabs (depending on the phosphorus content). It tends to increase the number of stacked M0S2 layers. These modifications might lead to the following positive effects on the catalyst ... 

In order to improve the textural properties of particle-clay nanohybrids, bulky organic cations are intercalated as a kind of template into particle-intercalated clays before stabilization procedures. Intercalation of the organic cations results in the removal of some of the intercalated nanoparticles and/or in their rearrangement. Subsequent calcination leads to formation of additional pore space that is highly correlated to the geometry and size of the templates. This technique allows fine tuning of textural properties in the preparation of particle-clay nanohybrids. The clay nanohybrids intercalated with metals, oxides, and complexes have a broad range of applications. In particular, metal oxide particle-pillared clays have excellent potentials as catalysts, catalyst supports, selective adsorbents, etc. " ... 

Ceria is effective in the removal of trace amounts of toxic metal species and radionuclides from aqueous solutions and contaminated soils [17], The behaviour of hydrous ceria as selective anion exchanger has also been described in the literature [18] For these applications the preparation of high surface area, thermally and chemically stable ceria phases as well as the study of the parameters which control structural and textural properties of the solid are of particular interest, as they are in the case of the automobile exhaust catalysts... 

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