Silica molecular sieves

Flanigen E M, Bennet J M, Grose R W, Cohen J P, Patton R L, Kirchner R M and Smith J V 1978 Silicalite a new hydrophobic crystalline silica molecular sieve Nature 271 512-16... 

Other covalently bonded catalysts are those on inorganic supports such as silica, molecular sieves (zeolites), and alumina, the complexes being held either directly via the oxygen of surface hydroxy groups or via an intermediate functional group, again especially phosphino. 

The early evolution of aluminosilicate zeolites, in the 1950s to 1970s, is summarized in Table 1.2, based on increasing framework Si/Al composition. The four somewhat arbitrary categories are (i) low , (ii) intermediate , (hi) high silica zeolites and (iv) silica molecular sieves. 

In summary, when we compare the properties of the low and intermediate zeolites with those of the high silica zeolites and silica molecular sieves, we find that their resulting properties allow the low and intermediate zeolites to remove water from organics and to carry out separations and catalysis on dry streams. In contrast, the hydrophobic high silica zeolites and silica molecular sieves can remove and recover organics from water streams and carry out separations and catalysis in the presence of water. 

A broad range of high silica and pure silica molecular sieves have been synthesized by employing hydrothermal synthesis in fluoride media at low H2O concentration, near neutral pH and alkali-free [81]. The significant new pure silica zeolite, lTQ-29, a structural analog of zeolite A (LTA) was reported by Corma at al [82]. Unlike the highly hydrophilic zeolite A, the ITQ-29 is hydrophobic. 

Zones, S.I., Hwang, S.-J., Elomari, S., Ogino, L, Davis, M.E., and Burton, A.W. (2005) The fluoride-based route to all-silica molecular sieves a sttategy for... 

Synthesis of mesoporous silica molecular sieves via a novel templating scheme... 

XRD patterns of the sample prepared mesoporous silica molecular sieves. 

Figure 2. XRD patterns of as-synthesized LZC mesoporous silica molecular sieves with different pH. (A) 2, (B) 7. (C) 10...

Properties of LZC mesoporous silica molecular sieves with different aging time... 

Figure 5. Nj adsorption/desorption isotherms of calcined LZC mesoporous silica molecular sieves with different surfactant/SiOj (A) 0.1, (B) 0.2. (C) 0.5, (D) 1.0, and (E) 1.5...

Natural gas liquids are recovered from natural gas using condensation processes, absorption (qv) processes employing hydrocarbon liquids similar to gasoline or kerosene as the absorber oil, or solid-bed adsorption (qv) processes using adsorbants such as silica, molecular sieves, or activated charcoal. For condensation processes, cooling can be provided by refrigeration units which frequently use vapor-compression cycles with propane as the refrigerant or by... 

Materials with very high Si/Al ratios (tending to infinity) are called all-silica molecular sieves, zeosils or porosils. If any aluminium is present, non-framework cations such as alkaline or alkaline earth metals... 

N(16)-methylsparteinium as a structure-directing agent to synthesize the high-silica molecular sieve with the AFI topology. Wagner et al. followed this work with the synthesis of CIT-5 (CFI) that is a high-silica molecular sieve with a 14-membered ring pore [29, 30]. 

The following two quatemized sparteine derivatives were synthesized recently and their performances in high-silica molecular sieve syntheses were investigated and compared [31]. 

Chromium-containing mesoporous silica molecular sieves (Cr-HMS) with tetrahedrally coordinated isolated chromium oxide (chromate) moieties can operate as efficient photocatalysts for the decomposition of NO and the partial oxidation of propane with molecular oxygen under visible light irradiation (Yamashita et al., 2001). 

The O2 isotherms for these AlPO molecular sieves are essentially Type I, typical of micropore filling (12,13). In Figure 16 the O2 isotherms of AlP0i.-5, -11, -17 are compared with those of a typical zeolite, NaX, and a silica molecular sieve, silica-lite. A1P04-5 and -17 have saturation pore volumes of approximately 0.2 cm /g similar to that of silicalite, while A1P0 -11 has a relatively small O2 pore volume (ca. 0.1 cm3/g). 

The surface character of the AlPO molecular sieves differs from that of the silica molecular sieves even though both framework types are neutral with no extra-framework cations. The molecular sieve silicalite is hydrophobic and the AlPO molecular sieves are moderately hydrophilic. Zeolites are hydrophilic due to the interaction of the dipole of the Hz0 molecule with the electrostatic fields of the anionic aluminosilicate framework and the balancing nonframework cations. The hydrophilicity of the AlPOi, materials is apparently due to the difference in electronegativity between Al(1.5) and P(2.1). Neither mechanism is possible with silica molecular sieves. The AlPOi, molecular sieves do exhibit less affinity for HzO than the hydrophilic zeolites such as Type A and Type X. 

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