In a method of synthesizing a mostly CHA-type silicoaluminophosphate
sieve, a reaction mixture comprises sources of water,
silicon, aluminum,
phosphorus, and a template. In one aspect, the
inorganic phosphorus and
silicon sources are first combined to form a primary mixture that is aged. Then, the aluminum source is added, followed optionally by any
organic phosphorus source, and then the template, to form the synthesis mixture. After heating at <10° C. / hr to induce
crystallization, in this aspect, both the crystallized
sieve has an average
crystal size ≦1.5 μm and / or is recovered in a yield of ≧10.0 wt %. In another aspect, when the synthesis mixture Si / Al2 ratio is <0.33,
crystallization is induced. Advantageously, the
sieve so crystallized has a template efficiency of ≧0.5 and / or is recovered in a yield of ≧10.0 wt %. The
molecular sieve from both aspects can be used in a
hydrocarbon (oxygenates-to-olefins) conversion process.