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Low dimensionality is a multifarious concept which applies to very diversified materials. Thus, examples of low-dimensional systems are structures with one or several layers, single lines or patterns of lines, and small clusters isolated or dispersed in solid systems. Such low­ dimensional features can be produced in a wide variety of materials systems with a broad spectrum of scientific and practical interests. These features, in turn, induce specific properties and, particularly, specific transport properties. In the case of zeolites, low dimensionality appears in the network of small-diameter pores of molecular size, extending in one, two or three di­ mensions, that these solids exhibit as a characteristic feature and which explains the term of'molecular sieves'currently used to name these ma­ terials. Indeed, a large number of industrial processes for separation of gases and liquids, and for catalysis are based upon the use of this low­ dimensional feature in zeolites. For instance, zeolites constitute the first class of catalysts employed allover the world. Because of the peculiarity and flexibility of their structure (and composition), zeolites can be adapted to suit many specific and diversified applications. For this reason, zeolites are presently the object of a large and fast-growing interest among chemists and chemical engineers.

The first symposium on Access in Nanoporous Materials was held in Lansing, Michigan on June 7-9, 1995. The five years that have passed since that initial meeting have brought remarkable advances in all aspects of this growing family of materials. In particular, impressive progress has been achieved in the area of novel self-assembled mesoporous materials, their synthesis, characterization and applications. The supramolecular self-assembly of various inorganic and organic species into ordered mesostructures became a powerful method for synthesis of mesoporous molecular sieves of tailored framework composition, pore structure, pore size and desired surface functionality for advanced applications in such areas as separation, adsorption, catalysis, environmental cleanup and nanotechnology.In addition to mesostructured metal oxide molecular sieves prepared through supramolecular assembly pathways, clays, carbon molecular sieves, porous polymers, sol-gel and imprinted materials, as well as self-assembled organic and other zeolite-like materials, have captured the attention of materials researchers around the globe.The contents of the current volume present a sampling of more than 150 oral and poster papers delivered at the Symposium on Access in Nanoporous Materials II held in Banff, Alberta on May 25-30, 2000. About 70% of the papers are devoted to the synthesis of siliceous mesoporous molecular sieves, their modification, characterization and applications, which represent the current research trend in nanoporous materials. The remaining contributions provide some indications on the future developments in the area of non-siliceous molecular sieves and related materials. This book reflects the current trends and advances in this area, which will certainly attract the attention of materials chemists in the 21st century.

The original properties of mesoporous molecular sieves are so unique that the design of most existing catalysts could be reconsidered. It might indeed be of interest to introduce MMS either as a support or as the active phase, merely on the basis of their high surface areas, narrow pore size distribution and flexibility in composition. The recent literature provides examples of MMS based catalysts of many types such as acid-base solids, supported metals and supported oxides, mixed oxides, anchored complexes and clusters, grafted organic functional groups and others. Examples of all these developments are documented in the present proceedings including some spectacular new proposals. The new metallic (Pt) mesophases are specially worth mentioning because they represent a new approach to producing non-supported highly dispersed metals.In these proceedings the reader will find feature articles and regular papers from many worldwide groups, covering all aspects of synthesis, physical characterization and catalytic reactivity of MMS and their chemically modified forms. It is actually remarkable that this recent development brought together an even broader spectrum of scientists from traditionally unrelated fields such as those of liquid crystals, surfactants, sol-gels, amorphous oxides and mixed oxides, solid state, adsorbents and heterogeneous catalysts. Obviously, this is a fast-growing research area which triggers the imagination and creativity at the cross-road between material design, molecular surface tailoring and catalytic applications.