The low-frequency capabilities of infrared emission spectroscopy (IRES) were exploited to examine the reduction of vanadium pentoxide (V2O5) by ammonia and hydrogen, and the reoxidation of reduced vanadia by oxygen. The catalytic reduction of NO with NH3 over V2O5 powder in the absence of O-2 was also investigated with IRES. The reduction of V2O5 was found to occur stepwise (V5+ -->t V4+ --> V3+), With the rate being controlled by the diffusion of oxygen through the crystal lattice. Vanadia reduction occurred even in high NO/NH3 atmospheres, although the presence of NO did effect the rate of reduction.