IR spectra of the compound CoWO4 and samples of the composition WO3–Co3O4: (a) CoWO4, synthesis 650 °С, 2 h, (b) CoWO4, synthesis 650 °С, 2 h, after exposure to a gas-air mixture containing 3.6 ppm NO2 (T = 187 °C, t = 30 min.), (c) 5 wt.% Co3O4, 450 °C, 2 h, (d) 15 wt.% Co3O4, 450 °С, 2 h.