| Since the optimization of the first zeolite synthesis in the 1930's, hundreds of new zeolite structures were synthesized and characterized, and a great number of new applications were discovered. The knowledge of material science has since then evolved in such a way that, at this stage, materials are purpose-designed. It is now realistic to say that zeolites have become ‘the’ most important catalyst and adsorber in industry, representing a market of billions of dollars.; However, the first zeolite applications were limited to small molecules, as the diameters of the galleries (pores) within the zeolites were quite narrow (<2 nm or microporous). The scientist's major task was then to enlarge these pores to ensure access for larger molecules. It was finally ExxonMobil, which, in 1992, gave the first full synthesis description and characterization of structures with large pores ordered in a particular way and having a unique diameter. They managed to place the pore diameter within the mesoporous region (2nm < x < 50nm). To this end they used large molecules, which form micelles and play the role of scaffolding, around which an inorganic framework can polymerize. By adapting the synthesis, it was even possible to vary the pore diameter in a very precise way. This permitted the field of applications to be broadened to a whole new series of large molecules of various dimensions. It even became possible to design applications for large biological molecules.; ExxonMobil's publication of the synthesis report in the journal Nature was the key signal for the start of a tremendous adventure in the development of mesoporous materials. To this day, this Nature article has been referenced more than 2800(!) times in just 10 years, clearly underlining the enormous impact it had on the material science community. More than 5000 (!!) published papers have treated the subject of mesoporous materials over less than 10 years.; The first papers describing the mesoporous samples, published by ExxonMobil, presented them as nano design or special pore architecture. The materials were no longer structured by the atoms but by the particular pore ordering in the structure. Two major structures were presented: the MCM-41 structure—with pores arranged in a closed hexagonal packing arrangement—and the MCM-48 material—possessing a cubic unit cell within two interwoven pore systems, progressing along three dimensions.; The ease of synthesis of MCM-41 quite rapidly attracted the attention of the majority of researchers. MCM-48, on the other hand, even if its 3D pore system was very promising for the diffusional possibilities it offered in various applications, remained very unpopular as a structure. (Abstract shortened by UMI.)... |
