CAL-4: A SAPO-44 analogue prepared from lamellar aluminophosphate

Normal-butylammonium lamellar aluminophosphate has been used as the source of aluminum and phosphorous atoms in the synthesis of CAL-4, a chabazite-like structure analogous to SAPO-44, in a reaction with silica and using cyclohexylamine as structure directing agent. By using the lamellar reactant, the concentration of organic structure directing agent is diminished to one-third of the value in the literature, without contamination of the product with other phases. The use of such reactant has given particular properties to the solid materials produced, especially in relation to the morphology; the intergrown rhombohedra usually found for SAPO-44 are also observed, however, the presence of the plates on the crystals surface is clear. Monitoring the reaction by physico-chemical techniques has shown that only after 36 h reaction Brönsted acid sites are formed and these protonate the cyclohexylamine and thus the cyclohexylammonium ion is incorporated in the structure in the final stages of the synthesis with the simultaneous intensive formation of structural double six-rings. Although 13C-MAS-NMR and FTIR have shown that n-butylamine and cyclohexylamine are both present in the channels and cavities of the solid, the key molecule in the structure directing complex is the cyclohexylammonium; the n-butylammonium is a part of the organic complex but has no role on the D6R formation or silicon incorporation. In fact, cyclohexylammonium, n-butylammonium and water seem to be involved in the formation of this molecular sieve.