Thermal stability aluminophosphate molecular

The characteristics of aluminophosphate molecular sieves include a univariant framework composition with Al/P = 1, a high degree of structural diversity and a wide range of pore sizes and volumes, exceeding the pore sizes known previously in zeolite molecular sieves with the VPI-5 18-membered ring material. They are neutral frameworks and therefore have nil ion-exchange capacity or acidic catalytic properties. Their surface selectivity is mildly hydrophilic. They exhibit excellent thermal and hydrothermal stability, up to 1000 °C (thermal) and 600 °C (steam). 

The introduction of silicon into hypothetical phosphorus sites produces negatively charged frameworks with cation-exchange properties and weak to mild acidic catalytic properties. Again, as in the case of the aluminophosphate molecular sieves, they exhibit excellent thermal and hydrothermal stability. 

The aluminophosphate molecular sieves have an interesting property for potential use as catalyst supports, due to their excellent thermal stabilities and unique structures. AIPO4-5 is known to retain its structure after calcination at 1000°C and have uni-directional channels with pore size of 8 A bounded by 12-membered rings [2]. To utilize molecular sieves as catalyst support, chemical interactions between the molecular sieve and active component, chemical stabilities, and surface structures must be determined. However, iittle attempt has been made to clarify the surface structures or properties of catalytically active components supported on the aluminophosphate molecular sieves. 

The pore structure of AlPO-n is interesting, not only for basic research but also for more applied research in catalysis. In particular, the aluminophosphate molecular sieves with extremely large pore diameters, 18-membered oxygen ring (known as VPI-5), are expected to lead to new applications despite their low thermal stability. 

Application of Aluminophosphate- based Molecular Sieves for a Thermostable Catalyst. - Although the high thermal stability is a particularly interesting property of aluminophosphate molecular sieves compared to those of aluminosilicate zeolites, the application of aluminophosphate molecular sieves as thermostable catalysts has been limited. In this section, the application of SAPO as thermostable NO reduction catalysts... 

Drs. Ishihara and Takita focus on a specific catalyst, the aluminophosphate molecular sieves. These materials have some useful properties that distinguish them from the more widely used aluminosilicates. These include generally milder acidity, somewhat different ion exchange properties, and higher thermal stability. This allows them to be used in a number of reactions in which aluminosilicates are not suitable, such as low-temperature catalytic combustion. 

The binary altuninophosphate molecular sieve family AIPO4 exhibits constant chemical composition with an A1 to P ratio of unity. This fixed composition provides electrically neutral framework structures. Consequently, there are no extra framework cations or protic acidity. The binary aluminophosphates are mildly hydrophilic, in contrast to the strongly hydrophilic zeolites and hydrophobic silica molecular sieves. The AIPO4 crystals generally have excellent thermal and hydrothermal stability, similar to that of stable zeolites. 

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