Microporous zeolites and mesoporous

Walcarius A (1999) Zeolite-modified electrodes in electrochemical chemistry. Anal Chim Acta 384 1-16 Walcarius A (2008) Electroanalytical applications of microporous zeolites and mesoporous (oigano)silicas recent trends. Electroanalysis 20(7) 711-738... 

Although catalysis is potentially one of the most important applications of metal-organic porous materials, as was the case for microporous zeolites and mesoporous materials, only a handful of examples have been so far reported for MOFs [128-131]. For catalytic applications using metal-organic open-framework materials, apparently five types of catalyst systems or active sites have been utilized ... 

Some important metal oxide materials that have used molecular and supramole-cular templates to direct structure formation are the zeolites and related semi-crystalline aluminosilicates. In this section we shall discuss the use of ammonium cations that direct formation of microporous zeolites and finish with some of the possibilities that exist with the use of surfactant systems and molecular aggregates to create mesoporous structure. Excellent books and reviews are suggested for additional reading into the detailed description of the art [58-60]. The intention of this section is to briefly introduce this area and describe the types of materials being produced using various imprinting techniques in metal oxide materials. 

Finally, Vroon et al. [82,97] reported the synthesis of continuous porous films of ZSM5 on top of y-alumina supported membranes (pore diameter 4 nm) by slip-casting with a zeolite crystal suspension. The porous zeolite layers (thickness 1-2.5 pm) consist of densely packed zeolite crystals with a diameter of 70-80 nm and with micropores in the zeolite and mesopores (diameter 8-24 nm) between the zeolite particles. This zeolite layer can be used as a support for further processing, e.g., pore filling of the mesopores or deposition of catalysts. First experiments by Vroon et al. to fill the mesopores by in situ crystallisation of MFI in the pores did not result in gas-tight membranes... 

Research on zeolites and mesoporous materials depends critically on the availability of characterization techniques that provide information on their electronic and structural properties. Many techniques (e.g. XRD, NMR, XAFS, UV-V1S, IR, Raman) provide information about bulk properties whereas surface sensitive techniques (e.g. XPS, SIMS, LEIS) will provide information from the surface of the particles of porous materials. For modern research spatially resolved information is indispensable, in particular with the advent of complex hierarchical materials that combine micropores and mesopores. For the latter sake, electron microscopy is of growing importance for the study of molecular sieves as is also apparent from the number of papers published on this topic over the last ten years (Fig. 1). Please note that the almost four-fold increase in papers over the last ten years about electron microscopy on molecular sieves far outnumbers the relative increase of the total number of papers on molecular sieves (increase by factor 1.4). 

The development of environmentally friendly solid catalysts for the production of fine chemicals has known a recent growing interest and recent review articles have been devoted to catalysis by solid bases. Several solid bases have been proposed such as alkali ion-exchanged zeolites [1], alkaline oxides supported on microporous [2] and mesoporous solids [3], sodium metal clusters in zeolites... 

With the advent of mesoporous materials to complement the microporous zeolites, there will be many more developments in the applications of silicate-supported reagents, limited only by the ingenuity and inventiveness of researchers. With increasing pressure from governments for the adoption of more environmentally friendly practices by the chemical industry, the use of framework silicates to provide clean technology can only increase. Zeolites and mesoporous materials offer versatility in application, ease of manufacture, inherent non-toxicity, and convenience of handling, which will ensure their long and varied future, both in industry and in everyday life. 

The regeneration of supercritical carbon dioxide from a mixture containing caffeine by microporous MFI zeolite and mesoporous silica membranes supported on alumina was studied. The experimental data show that a caffeine rejection higher than 90% or 70% and a permeation flux of supercritical carbon dioxide more than 0.05 or 0.07 mol/m /s could be obtained at 10.5 MPa. 

R. Millini, L.C. Carlucdo, A. Carati and W.O. Parker, Microporous Mesoporous Mater., 2001, 46, 191 J. Plevert, F. Di Renzo and F. Fajula, 2001, Stud. Surf. Sci. Catai, 135(Zeolites and Mesoporous Materials at the Dawn of the 21st Centnry), 2038. 

Perego C, Bosetti A. Biomass to fuels the role of zeolite and mesoporous materials. Microporous Mesoporous Mater 2011 144 28-39. 

A vast amount of research has been undertaken on adsorption phenomena and the nature of solid surfaces over the fifteen years since the first edition was published, but for the most part this work has resulted in the refinement of existing theoretical principles and experimental procedures rather than in the formulation of entirely new concepts. In spite of the acknowledged weakness of its theoretical foundations, the Brunauer-Emmett-Teller (BET) method still remains the most widely used procedure for the determination of surface area similarly, methods based on the Kelvin equation are still generally applied for the computation of mesopore size distribution from gas adsorption data. However, the more recent studies, especially those carried out on well defined surfaces, have led to a clearer understanding of the scope and limitations of these methods furthermore, the growing awareness of the importance of molecular sieve carbons and zeolites has generated considerable interest in the properties of microporous solids and the mechanism of micropore filling. 

Most of the microporous and mesoporous compounds require the use of structure-directing molecules under hydro(solvo)thermal conditions [14, 15, 171, 172]. A serious handicap is the application of high-temperature calcination to develop their porosity. It usually results in inferior textural and acidic properties, and even full structural collapse occurs in the case of open frameworks, (proto) zeolites containing small-crystalline domains, and mesostructures. These materials can show very interesting properties if their structure could be fully maintained. A principal question is, is there any alternative to calcination. There is a manifested interest to find alternatives to calcination to show the potential of new structures. 

A new composite containing montmorillonite and zeolite Beta is prepared by in situ crystallization. Nano-zeolite Beta grows on montmorillonite. The composite possesses a dual system of micropore, originated from zeolite Beta, and mesopore of size around 50nm, due to the abundance of interspace formed by montmorillonite laminaes. Compared with catalyst MoNi/Beta, more i-C8 is produced on catalyst MoNi/composite, when n-Cg is used for feedstock for hydroisomerization. This results from the high diffusion created by composite and the short channel of nano-size zeolite Beta. 

Acidic micro- and mesoporous materials, and in particular USY type zeolites, are widely used in petroleum refinery and petrochemical industry. Dealumination treatment of Y type zeolites referred to as ultrastabilisation is carried out to tune acidity, porosity and stability of these materials [1]. Dealumination by high temperature treatment in presence of steam creates a secondary mesoporous network inside individual zeolite crystals. In view of catalytic applications, it is essential to characterize those mesopores and to distinguish mesopores connected to the external surface of the zeolite crystal from mesopores present as cavities accessible via micropores only [2]. Externally accessible mesopores increase catalytic effectiveness by lifting diffusion limitation and facilitating desorption of reaction products [3], The aim of this paper is to characterize those mesopores by means of catalytic test reaction and liquid phase breakthrough experiments. 

Zeolite samples (NaY. Na-mordenite and Na-ZSM-5) were prepared in Research Institute for Petroleum and Hydrocarbon Gases in Bratislava. A mesoporous alumina, the carrier for reforming catalyst was used. Porosity of pure mesoporous alumina evaluated by t-plot method did not show the presence of micropores within the range of accuracy of 0.001 cm3/g. Mixtures of zeolites with mesoporous alumina were prepared on the base of dried samples in 5% steps. The prepared mixtures of alumina with zeolite were homogenized in vibration mill. 

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