Isolated acid sites were selectively generated by postsynthesis modification of a borosilicate zeolite beta. To this end, samples were prepared with pairs of adjacent boron sites balanced by Ca2+ ions, whereas isolated boron in the zeolite framework was balanced by NH4+ ions. To avoid undesired boron leaching, these ion exchange reactions were carried out in methanol solution rather than in water. Trigonal boron forms near the NH4+ ions by decomposing the latter into NH3 (and a proton), and selective extraction of the trigonal boron is achieved by water treatment, whereas the tetrahedral boron near Ca2+ ions remains in the zeolite framework. The vacancies were refilled with aluminum by treatment with an aqueous Al(NO3)3 solution. Two Bronsted acid sites with 1H chemical shifts of 4.0 and 5.0 ppm exist in the dehydrated samples. 1H–27Al REAPDOR solid-state NMR measurements yield quantitative information on the local H–Al distances of isolated H–Al two-spin and H–Al–Al three-spin systems. The nearest H–Al d...