A Comparative Study of the Activity of Oxide Catalysts in the Oxidation of Methane and 1,1-Dimethylhydrazine

The catalytic oxidation of methane and 1,1-dimethylhydrazine ((CH₃)₂N–NH₂, unsymmetrical dimethylhydrazine (UDMH)) with air on oxide catalysts was studied. Two pairs of perovskites (Ca_0.7Sr_0.3FeO_2.5(3.0) and La_0.7Sr_0.3CoO_2.5(3.0), stoichiometric and superstoichiometric with respect to oxygen) and a supported spinel (20%(Cu _x Mg_{1 – x} Cr₂O₄)/-Al₂O₃, IC-12-73) were used as catalysts. The experiments were performed using two laboratory flow-type systems: in a catalytic fixed-bed reactor (the oxidation ofCH₄) and in a gradientless vibrationally fluidized bed reactor (the oxidation of CH₄ and UDMH) at 150–700°C. In the oxidation of CH₄, the IC-12-73 catalyst was more active than the perovskite catalysts, although particular perovskite catalysts can exhibit higher activity in the region of low temperatures. In the oxidation of UDMH, the activity of perovskites in the test temperature region was lower than that of IC-12-73; this correlates with the higher activity of IC-12-73 in the oxidation of CH₄. The Ca_0.7Sr_0.3FeO_3.0 and La_0.7Sr_0.3CoO_2.5(3.0) perovskites exhibited similar activities in the deep oxidation of UDMH, which were higher than the activity of Ca_0.7Sr_0.3FeO_2.5. A comparison between the selectivities of the conversion of fixed nitrogen, which is a constituent of UDMH, into nitrogen oxides demonstrated that, on all of the perovskites, S ^N _NO was higher and was lower than the corresponding values on IC-12-73. Additional information on the possible mechanisms of intermediate formation in the adsorption and oxidation of UDMH on IC-12-73 was obtained using Fourier transform IR spectroscopy.