Hierarchical materials

In view of catalytic potential applications, there is a need for a convenient means of characterization of the porosity of new catalyst materials in order to quickly target the potential industrial catalytic applications of the studied catalysts. The use of model test reactions is a characterization tool of first choice, since this method has been very successful with zeolites where it precisely reflects shape-selectivity effects imposed by the porous structure of tested materials. Adsorption of probe molecules is another attractive approach. Both types of approaches will be presented in this work. The methodology developed in this work on zeolites Beta, USY and silica-alumina may be appropriate for determination of accessible mesoporosity in other types of dealuminated zeolites as well as in hierarchical materials presenting combinations of various types of pores. 

Figure 3.12 (Upper) Transmission electron to D. These structures range over a hundred micrographs of hierarchical materials micrometers, (b) Repetition element of the...

As the further step in the synthesis of this hierarchic materials, micro/macroporous composites were synthesized although it is not clear at the moment whether such materials can be used in catalysis [103,104]. 

The first successful preparation of micro/mesoporous or micro/macroporous molecular sieves as well as mesoporous zeolite single crystals started an intensive search of optimization procedures for their synthesis, to increase their thermal stability and to tailor their acid, base and redox properties for possible applications in heterogeneous catalysis. There is no doubt that mastering of synthesis of these hierarchic materials is an important challenge in the area of porous materials. 

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). 

Functionalization of the walls (also discussed in Sect. 8) in a hierarchical material is the hnchpin for potential appHcations in fields like separation and chromatography, electrochemical or pH sensing, and many more. 

Yao, H. and Gao, H. (2007) Multi-scale cohesive laws in hierarchical materials. International Journal of Solids and Structures, 44, 8177—8193. 

Controlling the organization of macromolecular building blocks on the secondary stracture level paves the way to generate more complex stmctures, which might lead to hierarchical materials. The previous section discussed recent examples of... 

With a view to providing materials with adjustable porosity, new conceptual developments in the field of hierarchical materials and structured systems are addressed below. 

All these concepts—enabling technologies, physical manifestations, functions, integration in and integration on, textiles as hierarchical materials, as well as stimulus and response from and to the textile artefact vis-a-vis the surroundings—form the fundament on which the text is based. 

By introducing a mixture of guest species, the differential curvatures of each succeeding layer of the vesicular mesophase would selectively position different species at different radial positions. This approach could lead to radially graded hierarchical materials that might facilitate vectorial energy transfer as in photosynthesis centers. 

It is seen that complex mechanisms are involved in die formation of these hierarchical materials. Similar to the structure motives on different length-scales cells, vesicles, supra-molecular structures, and biomolecules are involved in the structuring process of inoiganic matter occurring in nature. This process is commonly known as biomineralization [73]. 

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