The competition of organic amines and the phosphorus source on directing the formation of aluminophosphate-based molecular sieves with chabazite structure

In the report, H3PO3 was used in place of H3PO4 as the phosphorus source to synthesize chabazite structure silicoaluminophosphate (SAPO) molecular sieves, SAPO-34, SAPO-44, and SAPO-47. It has been found that the directing effects of organic bases have met with a competition coming from the alternation of phosphorus source. For example, using H3PO4 as the phosphorus source, morpholine and triethylamine are two well known organic bases for directing the formation of SAPO-34. However, when H3PO3 or the mixtures of H3PO3 and H3PO4 are used as the phosphorus source, the directing product has changed from SAPO-34 to SAPO-47. Raman investigation has shown that there are some P(III) species in the intermediates for crystallizing SAPO-47. It means that chabazite structure SAPO molecular sieves are formed from a new route containing the transformation of P(III) to P(V) species. Meanwhile, the host–guest interactions between organic bases and SAPO framework have been studied and used to discuss why SAPO-47 is the preferable crystallizing product in the presence of H3PO3. Moreover, the competitive effect of phosphorus source H3PO3 on the synthesis of SAPO-47 has met its limitation when employing cyclohexylamine as the structure-directing agent. It has shown that no matter using H3PO3 or the mixture of H3PO3 and H3PO4 as the source of phosphorus, SAPO-44 is always the crystallizing product.