Adsorption properties, aluminophosphate molecular sieves

The ease of the redox reactions of metal cations in the framework suggests that metal cations can be easily substituted into the framework of aluminophosphate molecular sieves. The changes in the coordination of Al ions in the framework by the adsorption of some gases such as H2 have also been reported by some researchers. This has not been observed for aluminosilicate zeolites. Although no investigation has been performed on the influence of the framework environment on the catalytic properties of aluminophosphate molecular sieves, there is a possibility that the restricted redox properties of metal cations in the framework catalyze reactions which proceed over free metal cations, as with oxides or ion-exchanged zeolites. 

Several aluminophosphate molecular sieves with AEL topology structure were synthesized and modified by Pd for direct transformation reaction of -butane to isobutene. The effect of pore geometry of the molecular sieves was studied. Pd modified 10-member ring SAPO-11 and metal-substituted AlPO-l 1 and SAPO-11 showed high selectivity towards isobutene. The incorporation of metal into the molecular sieves had effect on the product distribution. Catalytic properties and the result of chemical adsorption of monoxide predicted the interaction between the transition metal for substitution and the supported palladium. 

The papers by Conner, Kaneko, Rouquerol, Unger and their co-workers underline the importance now attached to the determination of physisorption isotherms at very low levels of surface coverage or fractional micropore filling, i.e. in the region of very low p/p . Such high resolution adsorption (HRADS) measurements have been shown to be especially useful for the characterization of the adsorptive properties of zeolites, aluminophosphates and molecular sieve carbons. 

---