Stephen T. Wilson

Aluminophosphate molecular sieves and the periodic table

New generations of crystalline microporous molecular sieve oxides have been discovered based on the novel aluminophosphate family by incorporating one or more of an additional thirteen elements from the Periodic Table into the AIPO 4 framework. Elements incorporated include Li, Be, B, Mg, Si, Ga, Ge, As, Ti, Hn, Fe, Co, and Zn, spanning monovalent through pentavalent framework cationic species. The new materials comprise more than two dozen structures and two hundred compositions, including multi-element frameworks containing combinations of up to six framework cations. Pore sizes range from 0.3nm to 0.8nm encompassing small, intermediate and large pore structures. The new molecular sieves are synthesized by hydrothermal crystallization of reactive aluminophosphate gels containing the additional framework elements and an organic template. Proof of framework incorportion includes the formation of novel structures, the enhancement of catalytic activity, elemental analysis, and various spectroscopic evidence. The Bronsted acidity observed ranges from weakly to strongly acidic. This landmark discovery of new generations of molecular sieve materials represents a remarkable diversity in crystal structure and crystal chemistry, and offers a nearly unlimited number of design parameters to tailor adsorptive and catalytic properties.

Structural, Synthetic and Physicochemical Concepts in Aluminophosphate-Based Molecular Sieves

Abstract The aluminophosphate-based molecular sieves represent new generations of crystalline microporous oxides with one or more of an additional thirteen elements, Li, B, Be, Mg, Si, Ti, Mn, Fe, Co, Zn, Ga, Ge, As, incorporated into the AlPO4 framework. More than two dozen structure types have been reported and include framework topologies analogous to zeolites and a large number of novel structures. Proposed structural rules, coupled with TO2 stoichiometry elucidate the T-O bonding sequences, the mechanism of framework element incorporation, and the generation of negatively charged frameworks. The structure-directing role of the template is dominated by stereospecific space-filling and stoichiometry between the template and the framework, and is influenced to a lesser extent by framework charge compensation. Incorporation of many of the framework elements generates negatively charged frameworks, hydroxyl structure and Bronsted acidity. The hydroxyl infrared characteristics and the Bronsted acidity as measured by n-butane cracking rates depend both on the nature of the element and the structure type. The relationship of Bronsted acidity and hydroxyl structure appears to be much more complex than in the aluminosilicate zeolites.