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In this work a series of mixed iron-cobalt spinel catalysts was synthesized by solution combustion synthesis and doped with 3 wt% of palladium via incipient wetness impregnation. The catalysts were synthesized with different Co:Fe ratios, characterized from the structural and surface point of view (XRD, XRF, μRS, BET, FESEM), and tested toward the oxidation of methane in lean conditions, in gas mixtures containing from 0.5 to 2 vol% of CH. The temperature window for the catalytic activity of the undoped mixed iron-cobalt spinels spread from 350 to 650 °C. While lower iron substitution levels lead to a decrease in the spinel's activity, the catalyst with / of the cobalt in the CoO substituted with iron shows similar activity to the parent CoO. Although the materials were proved to be heterogeneous from the crystal phase point of view (a mixture of cobalt-iron spinels), the observed reactivity still depends on the amount of iron introduced during the synthesis. The addition of Pd lowered the temperature window for the catalytic activity to the range of 250-550 °C. The promoting effect of Pd is most evident for the pure CoO catalyst. In contrast to the Pd-free catalysts, the best activity of Pd-promoted samples was observed for the catalysts with the highest iron content. [ABSTRACT FROM AUTHOR]

In this work a series of cobalt spinel catalysts was synthesized by different methods and doped with 1 wt% of palladium via incipient wetness impregnation or solution combustion synthesis (SCS). Both undoped and Pd-doped spinels were characterized from the structural and surface point of view (XRD, XRF, μRS, BET, FESEM) and tested toward the oxidation of methane in lean conditions, in gas mixtures containing from 0.5 to 2 vol% of CH. These methane concentrations are typical of processes involving combustion of CH in lean conditions as the after-treatment of unconverted CH in compressed natural gas-fed vehicle exhausts, or the treatment of fugitive CH from leaks in coal mines. The temperature window for the catalytic activity of the undoped CoO materials spread from 350 to 600 °C. The preparation method affected the catalytic activity of undoped CoO, with the best catalytic activity related to the spinel prepared by SCS employing urea. The addition of 1 wt% of Pd lowered the temperature window for the catalytic activity to the range of 250-500 °C, with insignificant differences for the various preparation methods. The beneficial effect of Pd-doping was assigned to the enhancement of the reduction of cobalt in the oxide structure. [ABSTRACT FROM AUTHOR]