Vanadium oxo species have been introduced into the supercages of Y-zeolite by adsorption and decomposition of VOCl3 to produce catalysts for the study of the effects of oxo vanadium site isolation on catalytic reduction of NO with NH3. V-51 solid-state MAS-NMR of calcined samples with up to 4 V atoms per supercage show that Y-zeolite stabilizes vanadium with octahedral, V2O5-like square pyramidal, and most commonly, tetrahedral coordinations. Two distinct isolated tetrahedral environments were identified with NMR resonances around -530 and -830 ppm. There was no NMR evidence for oxygen bridge-bonded vanadia structures in the tetrahedral species in these catalysts. DRIFTS shows that ammonia adsorbs primarily on Bronsted acid sites associated with both the zeolite and the vanadium oxo species. DRIFTS during NO reaction with preadsorbed NH, shows the production of a hydroxyl species at 3690 cm(-1), which was assigned to V+4-OH, in agreement with the literature. Turnover frequencies, based on NO conversion and total vanadium loading, range from 1 x 10(-5) to 3 x 10(-4) s(-1) with selectivity to N-2 of 90-100%. Steady-state reaction experiments indicate that isolated vanadia species are viable sites for the catalytic reduction of NO.