Porous inorganic framework

The induction of steric effects by the pore walls was first demonstrated with heterogeneous catalysts, prepared from metal carbonyl clusters such as Rh6(CO)16, Ru3(CO)12, or Ir4(CO)12, which were synthesized in situ after a cation exchange process under CO in the large pores of zeolites such as HY, NaY, or 13X.25,26 The zeolite-entrapped carbonyl clusters are stable towards oxidation-reduction cycles this is in sharp contrast to the behavior of the same clusters supported on non-porous inorganic oxides. At high temperatures these metal carbonyl clusters aggregate to small metal particles, whose size is restricted by the dimensions of the zeolitic framework. Moreover, for a number of reactions, the size of the pores controls the size of the products formed thus a higher selectivity to the lower hydrocarbons has been reported for the Fischer Tropsch reaction. 

The N2 physisorption experiments on mesoporous NU-MGe-2 show typical type-lV adsorption branches with a distinct condensation step at relative pressure (P/Po) 0.16, suggesting well-defined mesopores. These materials have porous structure with BET surface areas in the range of 127-277 m /g, pore volumes in the range of 0.15-0.26 cm /g, and BJH pore sizes in the 2.7-2.8 nm range. These surface areas are reasonable if we consider the heavier inorganic frameworks and correspond to silica equivalent surface areas of 403-858 m /g. The framework wall thickness was found to be 2 run for mesoporous NU-MGe-2 (M = Sb, In, Sn, and Cd) and 2.4 nm for NU-PbGe-2, which is consistent with the larger diameter of the incorporated Pb atoms. 

The fluoride route of synthesis seems very rich and already provided four among the six most open frameworks described up to now in the litterature in the category of microporous compounds (0 < A) VSB-1 [22] cloverite [11], ULM-5 [23] and ULM-16 [24] with tunnels limited by 24, 20,16 and 16 polyhedra respectively. These four solids are really porous, the porosity being generated by the elimination of the template either by thermal or chemical methods which preserve the inorganic framework. 

Further variation of the stmctural and catalytic properties of four-coimected tetrahedral frameworks is obtained by the substitution of silicon or metal cations,giving materials known as SAPO s and MeAPO s, respectively. More than twenty metal aluminophosphate frameworks have been identified with Mg, Mn, Fe, Co, or Zn substituents. These give the possibility of framework redox activity (e.g. Fe +/Fe +) in catalysis as well as the usual Bronsted acidity. For further information about zeolitic and microporous phosphate frameworks see Porous Inorganic Materials and Zeolites) and recent reviews. ... 

The well-defined porous structure of zeolitic materials makes these materials true shape-selective molecular sieves. The presence of charge-compensating cations such as alkaline and alkaline earth cations, protons, etc. within the inorganic frameworks adds ion exchange and catalytic properties. Moreover, the hydrophobic nature of pure silica zeolites or the hydrophilic nature of aluminosilicates makes these solids useful as specific adsorbents of organic molecules or water in the gas or liquid phase. 

A typical infrared spectrum is collected between 400 and 4000cm , which enables most of the fundamental bands from the framework and hydroxyls to be measured. Some spectrometers permit measurement in the near IR (up to 7000cm ), so that overtones and eombination bands (much weaker than the fundamental resonances) ean also be measured. For porous inorganic solids empty of adsorbed speeies, fundamental hydroxyl stretches are observed in the range 3200-3800 cm and framework vibrations are observed in the range 400-1200 cm Organic species present (such as templates or the organic parts... 

A particularly interesting and important development in recent years has been the use of organic compounds as templates when forming porous inorganic phosphate structures, for example, 2D pillared layer or 3D cavity structures. These organic templates dictate the shape and size of the pores which are formed, and they can usually be removed from the inorganic framework afterwards. If their removal results in lattice collapse, the lattice should not be regarded as truly microporous [3]. 

---