Influence of Organic Templates on the Structure and on the Concentration of Framework Metal Ions in Microporous Aluminophosphate Catalysts

摘要

Energy minimization methods are used to investigate the packing energies of triethylamine and triethylammonium templates in two distinct aluminosilicate structures, AlPO_4-5 (AFI code) and the chabazitic AlPO_4-34 polymorph (CHA), both of which may be synthesized as Co-AlPOs from the same gel, depending on the concentration of Co~(2+) and template. We show that higher (cationic) concentrations of template, induced by higher (negatively charged) Co~(2+) substitution levels in the framework, favor the formation of a chabazitic structure. The AlPO_4-5 polymorph is, however, marginally more stable in the untemplated state, a result which is consistent with the reversion of the chabazitic phase to the AlPO_4-5 polymorph at higher temperatures or increased reaction time.