Abstract: Embodiments of crystalline, titanium silicate molecular sieves are described having a formula representing mole ratios of oxides of n M1O:TiO2:y SiO2:zH2O:wX where Mi refers to a metal cation or mixture of metal cations; n is from about 1 to about 2; y is from about 1 to about 10; z is from 0 to about 100; X is a halide anion other than fluorine, or combination of halide anions that excludes fluorine; and w is greater than 0. The pore size of the sieves can be adjusted by ion exchanging Mi cations with a suitable amount of another species. Embodiments of the invention are useful for various adsorptive fluid separation processes, including pressure swing adsorption processes. For example, disclosed embodiments are useful for separating methane from air.