Created mesoporosity

Acid leaching is decreasing the number of Bronsted acid sites (9,10) and creates mesoporosity inside the zeolite crystallites (11). This mesoporosity has been visualized by 3D TEM images (12). In that paper it has been shown that increasing... 

Hydrothermally dealuminated PER and sample that were subsequently acid treated exhibited better selectivities for isobutylene formation than an untreated PER catalyst (27). Furthermore, hydrothermally dealuminated PER exhibited a lower activity than untreated PER but higher selectivity for isobutylene 30,62,66). A subsequent acid treatment (with 5% HCl solution) further decreased the conversion and increased the isobutylene selectivity. The hydrothermal treatment created mesoporosity by A1 extraction. The A1 extraframework species were located in the mesopores and/or in the micropores. The HCl treatment removed part of the extraframework Al, leaving part in the micropores. The elimination of extraframework A1 from the mesopores was evidently beneficial for isobutylene selectivity. Evidently, the active sites associated with extraframework Al located in large voids are nonselective in contrast, extraframework Al located in the micropores (and not removed by acid treatment) does not contribute to catalytic activity. The steamed and acid-washed ferrierite exhibits excellent isobutylene selectivity and catalytic stability 30). 

A layer with a high specific surface area could be developed on woven glass fiber supports by leaching the nonsilica components out of commercial fabrics in acidic solution [54,62], This treatment created mesoporosity and specific surface areas between 5 and 275 m2 g, depending on the temperature and the contact time with HCI solution. In some cases, the surface of porous glass fibers was modified by titania, zirconia, or alumina to increase the thermomechanical stability and to vary the surface reactivity. The modification was made by impregnation of the porous glass fibers with aqueous solutions of the appropriate salts and subsequent calcinations in air. 

MFI zeolite upon alkaline treatment (see also Fig. 1) [6]. Following those results, an optimal framework Si/Al ratio of 25-50 for mesopore formation has been established. The fitting of the data in the range Si/Al ratio 50-200 was somehow arbitrary, due to lack of zeolites with a suitable Si/Al ratio. The increased mesopore surface area of 120 m g obtained upon desilication of FeS, coupled to a framework Si/Fe molar ratio of 77, however perfectly correlates with the previously proposed fitting, despite the different nature of the trivalent framework cation (solid circle in Fig. la). Additionally, the newly created mesoporosity centered around 20 nm also agrees well with the mesopore size vs. Si/Al ratio dependency, as shown in Fig. lb. These results provide supplementary convincing evidence of the crucial role of the trivalent metal cation in framework positions on the mesopore formation process, which appears to be independent on the nature of the trivalent metal cation. In addition, this confirms the universality of the pore formation mechanism as previously proposed for the alkaline treatment of MFI zeolites [18]. 

Mesopores were created in MFI zeolite by alkali treatment technique without deterioration of zeolitic microporous structure. The size of formed mesopore is ca. 4 nm and more uniform than that of MCM-41. Mesopores are formed along a boundary of MFI crystallite twinning, which shows a weak quality against alkalinity, apart from the microporous structures. This unique structure causes superiority in acid catalysis because of the combination of its strong acidity originated by ZSM-5 with newly created mesoporosity. 

This approach, developed by Fauchet, Striemer, and coworkers, creates mesoporosity via thermal anneal treatments of ultrathin (10-50 nm) silicon films (Fang et al. 2010). A typical process flow is shown schematically in Fig. 2. For silicon Aims sandwiched between silica layers, porosities up to 15 % were achieved. The potential in vitro and in vivo biomedical uses of such membranes are reviewed in the handbook chapter Porous Silicon in Immunoisolation and Biofiltration. Very recently, higher levels of porosity have been achieved using silicon nitride rather than oxide as the barrier layers (Qi et al. 2014). 

There are two ways, at least, to be considered. First, the carbonization process, itself, creates mesoporosity in the carbon by reason of the physical structure of the parent material, associated with shrinkage, etc., and is referred to as indigenous mesoporosity. The second method is where a non-mesoporous, but microporous carbon is activated physically by, for example, gasification with steam or carbon dioxide, when carbon atoms of the carbon structure (wherever they are) are gasified leaving molecular holes or created... 

Created mesoporosity is the result of controlled gasification (activation) by, for example, carbon dioxide or water vapor, of a microporous carbon at temperatures of about 700-800 °C. It is assumed that gasification occurs preferentially of carbon atoms at specific sites within the carbon particle because the activation process occurs uniformly within (throughout) the carbon sample and not just on the external surfaces or positions of initial collision. Further, it is noted that external surfaces of carbon samples may develop a mesoporosity that is cone-shaped (Figures 4.55 and 4.57). Such a mesopore would exhibit hysteresis in an adsorption experiment. However, the carbon gasification which occurs within a carbon particle, not on an external surface, may create mesoporosity which resembles a cave brought about by the excavation of carbon atoms (Figures 4.55 and 4.57). 

It was shown that compared to other frameworks (eg, MFI, MTW, MOR, and BEA), FER requires more severe conditions to extract silicon to create mesoporosity. The authors succeeded in increasing the mesopore surface area of the NaOH-treated ferrierite hy a factor of 3-4 with respect to the parent zeolite, while preserving the crystallinity and acidity. 

Powder packaging of carbon blacks creates clusters of particles. The spaces between the clusters yield mesoporosity. Packed carbon blacks provide a fair multipore-... 

A closer look at the mechanism of hydrothermal dealumination (hydrolysis of Si-O-Al bonds) illustrates that a healing process also takes place during this transformation (3), but contrary to the chemical substitution highlighted above, the source of Si originates from the zeolite, and results in a partial destruction of the zeolites and Si migration. The mesoporosity created during the process is beneficial to the diffusion of the large molecules of oil. 

In this work we have studied the effect of catalyst porosity on regeneration efficiency of FCC catalyst and shown that index of mesoporosity can very well explain the regeneration efficiency of FCC catalysts. We have also shown how different Pore Regulating Agents(PRA) can be used in catalyst formulation to create a desirable mesopore range of size distribution of FCC catalyst. 

The complete adsorption-desorption study of the nitrogen isotherm revealed that our sample of VPI-5 was microporous as well as mesoporous. The rapid rise in the volume within the relative pressure range less than 0.01 and upward trend of the rise in the volume thereafter are indicative of this phenomenon as can be seen in Figure 4. The desorption part of the isotherm traces the hysteresis loop similar to type A which is indicative of the presence of a mesoporosity created by a packing of the needle like crystals. 

Dealumination Dealumination creates mesopores by removal of a certain amount of the aluminum from the zeolite framework. This method represents the classic alternative route to develop mesoporosity in zeohtes, and mainly comprises two strategies, which are steaming at elevated temperatures and acid leaching. 

Many surfactants have been used as templates for creating inter/intrac-rystalline mesoporosity in zeolites. For example, Schuth et al. synthesized mesoporous silicalite-1 zeolite by using an organic aerogel as a soft template [33]. Similarly, Xiao et al. prepared structured zeolites templated by... 

Porous silicon has been fabricated by both top-down techniques from solid silicon and bottom-up routes from silicon atoms and silicon-based molecules. Over the last 50 years, electrochemical etching has been the most investigated approach for chip-based apphcations and has been utilized to create highly directional mesoporosity and macroporosity. Chemical conversion of porous or solid silica is now receiving increasing attention for applications that require inexpensive mesoporous silicon in powder form. Very few techniques are currently available for creating wholly microporous silicon with pore size below 2 nm. This review summarizes, from a chronological perspective, how more than 30 fabrication routes have now been developed to create different types of porous silicon. 

---