Nanohybrid materials made of h-BN nanoparticles (BNNPs) with Ag nanoparticles (AgNPs), covering their surfaces, were employed as catalysts in CO oxidation reaction. Ag/BN nanohybrids (NHs) were produced via AgNO3 decomposition under UV irradiation in polyethylene glycol (PEG) and its solutions at room temperature. Influence of the synthetic media composition on the synthesis process and resultant NHs structures were investigated. Two different structural types (Ag/BN and polymer-based structure) formed during the synthesis were studied. It was demonstrated that Ag/BN NHs synthesized in a PEG media had possessed the highest Ag concentration and uniform distribution of AgNPs. Catalytic activity tests revealed that the lowest temperature of full CO conversion (194 degrees C) had been attained to the sample with the highest Ag content. CO oxidation mechanism on the surface of AgNPs was finally proposed based on DFT calculations. (C) 2018 Elsevier Inc. All rights reserved.