A method for reducing the level of occluded alkali metal cations from an MSE-framework type molecular sieve comprises either (a) contacting the molecular sieve with a solution containing ammonium ions at a temperature of at least about 50° C. to ammonium-exchange at least part of the occluded potassium ions or (b) contacting the molecular sieve with steam at a temperature of at least about 300° C. and then subjecting the steamed molecular sieve to ammonium exchange.