Catalytic and physicochemical properties of Au nanoparticles and MxOy ( M=V,Mo,Cr) nanoclusters dispersed on oxide supports will be described. The reactions studied included total and selective oxidation reactions, related to environmental protection: oxidation of CO (also preferential PROX oxidation in the presence of hydrogen) and of C3 and C2 hydrocarbons. Correlations between molecular structure, physicochemical properties of the catalysts and catalysts' activity and selectivity will be shown and discussed. The accent will be put on the effect of nature of the oxide support on dispersion and properties of the active phase: metallic (nanoAu) or oxidic (MxOy clusters). For catalysts based on Au nanoparticles, the activity in CO oxidation increases with the support reducibility. Activity and selectivity in oxidation of hydrocarbons depends also on the support reducibility, nano-Au dispersed on non-reducible oxides of main group elements being more selective. For MxOy/oxide support catalysts an increase in activity and selectivity to partial oxidation products and decrease in the acidity, as compared with bulk MaOb oxides, have been found. Structure and properties of dispersed bidimensional MxOy clusters depend on the number of M atoms in the clusters and on nature of the support. Specific catalytic properties of MxOy nanoclusters as compared with bulk oxides are discussed in the light of the current theories of oxidation.