The paper presents original results on the of nitric acid concentrations effect on structure, morphology, protolytic properties and the activity of low-temperature carbon monoxide oxidation catalysts based on acid-modified phlogopite (X̅Н-Phl-1) and K2PdCl4, Cu(NO3)2, KBr base components. Samples (supports and catalysts) were characterized by XRD, SEM, FT-IR spectroscopy and pH metric method. It was found that only at Х̅≥ 3.0 mol/L, the phlogopite samples undergo structural and morphological changes and the pH of the suspension decreases, contributing to the achievement of such a catalyst activity, which ensures stable air purification from CO to a concentration below the MPCСО= 20 mg/m3 for the working area. The catalyst Pd(II)-Cu(II)/8H-Phl-1 can be recommended for use in respiratory devices.