Synthesis of silicoaluminophosphate molecular sieves

A method of synthesizing a silicoaluminophosphate molecular sieve comprising at least one intergrown phase of an AEI framework type material and a CHA framework type material, the method comprising:

• (a) preparing a first synthesis mixture comprising water and sources of phosphorus, aluminum and optionally silicon;
• (b) heating said first synthesis mixture under agitation to a first temperature of from about 99° C. to about 150° C. to form an intermediate product mixture containing a silicoaluminophosphate or aluminophosphate precursor material;
• and
• (c) cooling and storing the intermediate product mixture at a second temperature less than 50° C.;
• (d) preparing a second synthesis mixture comprising at least part of said intermediate product mixture from (c) and at least one organic directing agent and, if necessary, a silicon source to provide a SiO2:Al2O3 ratio within said second synthesis mixture of from about 0.05 to about 0.3;
• (e) heating said second synthesis mixture, under static conditions or with reduced agitation in comparison with that used during heating of said first synthesis mixture, to a third temperature higher than said first temperature and from about 150° C. to about 220° C. to convert at least part of said precursor material into said molecular sieve;
• and
• (f) recovering said molecular sieve.