Synthesis, amorphous material

This chapter discusses the synthesis, characterization and applications of a very unique mesoporous material, TUD-1. This amorphous material possesses three-dimensional intercoimecting pores with narrow pore size distribution and excellent thermal and hydrothermal stabilities. The basic material is Si-TUD-1 however, many versions of TUD-1 using different metal variants have been prepared, characterized, and evaluated for a wide variety of hydrocarbon processing applications. Also, zeolitic material can be incorporated into the mesoporous TUD-1 to take the advantage of its mesopores to facilitate the reaction of large molecules, and enhance the mass transfer of reactants, intermediates and products. Examples of preparation and application of many different TUD-1 are described in this chapter. 

Irrespectively of the iron content, the applied synthesis procedure yielded highly crystalline microporous products i.e. the Fe-ZSM-22 zeolite. No contamination with other microporous phases or unreacted amorphous material was detected. The SEM analysis revealed that size and morphology of the crystals depended on the Si/Fe ratio. The ZSM-22 samples poor in Fe (Si/Fe=150) consisted of rice-like isolated crystals up to 5 p. On the other hand the preparation with a high iron content (Fe=27, 36) consisted of agglomerates of very small (<0.5 p) poorly defined crystals. The incorporation of Fe3+ into the framework positions was confirmed by XRD - an increase of the unit cell parameters with the increase in the number of the Fe atoms introduced into the framework was observed, and by IR - the Si-OH-Fe band at 3620 cm 1 appeared in the spectra of activated Fe-TON samples. 

Another PET copolymer system that was recently demonstrated to be sufficiently stable to standard synthesis conditions, yet photochemically reactive, is that of PET-/ -phenylene bisacrylic acid (PBA) (Figure 6.9) [74], Upon UV irradiation, PET copolymers containing up to 15mol% of PBA were shown to irreversibly undergo [2 + 2] cycloaddition reactions to produce lightly crosslinked, amorphous materials. 

Another vanadium oxide that has received much attention is LiVaOs, which has a layer structure composed of octahedral and trigonal bipyramidal ribbons that can be swelled just like other layered compounds and can intercalate lithium. Here again, the method of preparation is important to its electrochemical characteristics. West et al. made a systematic study of the impact of synthesis technique on capacity and cycling and showed that amorphous material increased the capacity above 2 V from 3—4 lithium per mole of LiVsOs at low current drains, 6—200 fiAlcm. ... 

Eberl, D., 1970. Low-temperature synthesis of kaolinite from amorphous material at neutral pH. Conf. Clay Minerals Soc., 19th, Abstr., p. 17. 

Molecular Recognition and Chemistry in Restricted Reaction Spaces. Photophysics and Photoinduced Electron Transfer on the Surfaces of Micelles, Dendrimers and DNA [N. J. Turro, J. K. Barton, D. A. Tomalia, Acc. Chem. Res. 1991, 24, 332], Self-Assembly in Synthetic Routes to Molecular Devices. Biological Principles and Chemical Perspectives A Review [J. S. Lindsey, New J. Chem. 1991,15, 153], Amorphous molecular materials synthesis and properties of a novel starburst molecule, 4,4, 4 -tri(N-phenothiazinyl)triphenylamine [A. Higuchi, H. Inada, T. Kobata, Y. Shirota, Adv. Mat. (Weinheim, Ger.) 1991, 3(11), 549-550],... 

Another route for the production of materials involves the reaction of hydrolysis-condensation of metal alkoxides with water. We study here the important case of amorphous silica synthesis. In this case [38,39,44], silicic acid is first produced by the hydrolysis of a silicon alkoxide, formally a silicic acid ether. The silicic acids consequently formed can either undergo self-condensation, or condensation with the alkoxide. The global reaction continues as a condensation polymerization to form high molecular weight polysilicates. These polysilicates then connect together to form a network, whose pores are filled with solvent molecules, that is, a gel is formed [45],... 

The method generally used for the synthesis of amorphous [Si-Al] is by the appropriate combination of sodium silicate and sodium aluminate, as explained for the synthesis of aluminosilicate zeolites in Section 3.4.1. But, in this case, the gel is not hydrothermally treated in an autoclave in order to crystallize a zeolite. It is instead thermally dried (see Section 2.7.1) to obtain an amorphous [Si-Al], The produced amorphous material is then exchanged with NH4, using a method similar to that previously explained for zeolites ... 

NaOH 450 H2O at 95 °C, four identical non-stirred syntheses were carried out these syntheses were terminated after different time intervals. The composition of the solution was quantified at 95 °C by chemical trapping and the solid phase by XRD and elemental analyses (wt % Si, C, H, N). In this way a Si mass balance over the solution and the solid phase during the silicalite synthesis was obtained. The results are summarized in Table I, which also gives the results of a similar procedure for an analogous synthesis in the presence of DMSO. In this latter case, however, we were not able to filter the solution as thoroughly as in the first one, so that at the beginning of the synthesis a minor trace of amorphous material was present. 

The gas phase acid-catalyzed synthesis of pyridines from formaldehyde, ammonia and an alkanal is a complex reaction sequence, comprising at least two aldol condensations, an imine formation, a cyclization and a dehydrogenation (9). With acetaldehyde as the alkanal, a mixture of pyridine and picolines (methylpyridines) is formed. In comparison with amorphous catalysts, zeolites display superior performance, particularly those with MFI or BEA topology. Because formation of higher alkylpyridines is impeded in the shape-selective environment, the lifetime of zeolites is much improved in comparison with that of amorphous materials. Moreover, the catalytic performance can be enhanced by doping the structure with metals such as Pb, Co or Tl, which assist in the dehydrogenation. 

Additionally, the L. innocua ferritin-like protein served as a template for the controlled mineralization of two cobalt oxide phases Co(0)OH and C03O4 under two reaction temperatures of 23° and 65 °C, respectively. Substantial differences in crystallinity of the cobalt mineral core was observed between the two synthetic routes. The mineralization reaction carried out at higher temperatures yielded more crystalline nanomaterials, while the low-temperature synthesis tended toward amorphous material. The high crystallinity obtained at higher temperatures is most likely due to removal of structural waters present in the protein cavity and the surpassed energy barrier of nucleation at 65 °C. ... 

The synthesis of novel materials (particularly multicomponent materials) with unusual properties for uses as catalytic converters is gaining interest [72]. Thus, nanoporous structures of materials obtained by high-US agglomeration of monodispersed nanoparticles exhibit excellent properties and do not require the thermal post-treatment usually needed for the crystallization of amorphous materials or removal of surfactants [73]. 

After three hours the sample was removed from the spectrometer, washed and reanalyzed. The P MASNMR spectrum of this sample is presented in Figure 11. Washing the sample removes the amorphous material that is detected between 0 and -20 ppm. The excellent agreement between the results obtained from the autoclave experiments and the in-situ MASNMR spectroscopy experiments suggests the synthesis of VPI-5 can be studied directly inside a MASNMR spectrometer. 

---