A method of preparing a crystalline STT-type zeolite that has a mole ratio greater than about 15:1 of a tetravalent element oxide to a trivalent element oxide is disclosed along with a gas treatment system that incorporates the STT-type zeolite and a process for treating a gas using the STT-type zeolite. The method generally comprises forming an aqueous mixture comprising a tetravalent element oxide source, a trivalent element oxide source, a source of alkali metal, and an organic structure directing agent; maintaining the mixture under conditions that crystallize crystals of a STT-type zeolite; and recovering the crystals The STT-type zeolite crystals exhibit x-ray diffraction 2-theta degree peaks at: 8.26, 8.58, 9.28, 9.54, 10.58, 14.52, 15.60, 16.43, 17.13, 17.74, 18.08, 18.46, 19.01, 19.70, 20.12, 20.38, 20.68, 21.10, 21.56, 22.20, 22.50, 22.78, 23.36, 23.76, 23.99, 24.54, 24.92, 25.16, 25.58, 25.80, 26.12, 26.94, 27.38, 27.92, 28.30, 28.60, 29.24, 29.48, 30.08, 30.64, 31.20, 31.46, 31.80, 32.02, 32.60, 33.60, and 34.43.