Effect of organic templates on the kinetics and crystallization of microporous metal-substituted aluminophosphates

The formation of the microporous cobalt-containing aluminophosphate CoAPO-36 (ATS framework), synthesized using three different organic templates, tripropylamine (TPA), N,N-diisopropylisobutylamine (DPBA), and N-ethyldicyclohexylamine (ECHA), has been examined using in situ energy-dispersive X-ray diffraction (EDXRD). These measurements revealed that the type of template can significantly affect the rate of formation, the order being DPBA > ECHA > TPA. This observation is further supported by the measurement of induction times and activation energies (using the Arrhenius equation), which also follow the same trends. Further ex situ crystallographic studies of the as-synthesized materials have then shown that the template can also alter the size and symmetry of the unit cell of these materials. By combining these results with computational calculations on the size of each template and its packing within a representative section of the framework, we have shown that the bulky nature of the ECHA template is responsible for the changes in the unit cell, while the interaction energies between the template and the framework at different packing levels rationalize the EDXRD results, showing that the system with the most stable interaction energy will form more rapidly.