Patent ID: 8313727

Claim:
A method of preparing a silicoaluminophosphate molecular sieve having 90% or greater CHA framework-type character, the method comprising: (a) combining an inorganic source of phosphorus and a source of silicon, optionally with a liquid mixture medium, to form a primary mixture; (b) aging the primary mixture for an aging time and at an aging temperature sufficient to allow homogenization of the primary mixture, physico-chemical interaction between the source of phosphorus and the source of aluminum, or both; (c) adding a source of aluminum and optionally additional liquid mixture medium, to the aged primary mixture to form a secondary mixture; (d) (i) optionally adding an organic source of phosphorus to the secondary mixture and (ii) adding an organic template thereto, and optionally additional liquid mixture medium, to form a synthesis mixture having an Si/Al 2 ratio; (e) heating said synthesis mixture at a rate of less than 10° C./hour to a crystallization temperature within the range of about 150° C. to about 200° C.; (f) retaining said synthesis mixture within said crystallization temperature range for a crystallization time from 5 minutes to 350 hours to induce crystallization of a silicoaluminophosphate molecular sieve, which exhibits 90% or greater CHA framework-type character; and (g) recovering a crystallized silicoaluminophosphate molecular sieve from the synthesis mixture, wherein the crystallized silicoaluminophosphate molecular sieve exhibits a Si/Al 2 ratio less than 0.33 and exhibits a Si/Al 2 ratio that is not more than 0.10 greater than the Si/Al 2 ratio of the synthesis mixture, and wherein (i) the crystallized silicoaluminophosphate molecular sieve has a crystal size distribution such that its average crystal size is not greater than 1.5 μm; (ii) the yield of the sieve recovered from step (g) is at least 10.0 wt %; or (iii) both (i) and (ii).