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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]

A series of Pd/Co 3 O 4 catalysts with increasing palladium loading in the range of 0.5–5 wt.% was prepared by incipient wetness impregnation of Co 3 O 4 . Solution combustion synthesis with urea as a fuel was used to optimize the Co 3 O 4 reactive support for palladium in the combustion of methane in lean conditions. The obtained catalysts were thoroughly examined by XRD, XPS, XRF, RS, FESEM, H 2 -TPR, TGA, and N 2 -BET techniques. The catalytic tests of CH 4 combustion were performed for 0.5, 1, and 2 vol.% CH 4 , with constant lambda value. The obtained results revealed that a sub-stoichiometric fuel-to-oxidizer ratio, 0.75, results in the most catalytically active Co 3 O 4 phase. The important differences in the catalysts’ activity were apparent for the highest CH 4 concentration, with the 3% Pd/Co 3 O 4 being the most active catalyst. The observed activity was explained considering the physicochemical, spectroscopic, and microscopic characterization of the catalysts with the PdO nanocrystals surface distribution being the determining factor for the catalysts’ reactivity. A simple model accounting for the observed dispersion effect is proposed. The model is based on a two types of the interaction of the surface PdO active phase with the Co 3 O 4 support. Firstly, cobalt oxide helps to remove hydroxyl species from the PdO surface, thus making the active sites more available for methane activation. Secondly, cobalt spinel provides lattice oxygen to the PdO phase, again helping to recreate active sites thereon. [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]

In this work a series of palladium doped cobalt spinel catalysts was synthesized via solution combustion synthesis plus incipient wetness impregnation and tested in lean CH 4 oxidation. The obtained catalysts were characterized from the structural and surface point of view (XRD, XRF, μRS, BET). The Pd doping level, calculated as PdO, ranged from 0.5 to 5 wt.%. The optimal palladium loading was determined on the basis of catalytic tests in gas mixtures containing from 0.5 to 2 vol.% of CH 4 . The temperature window for the catalytic activity of the Pd/Co 3 O 4 materials spread from 270 to 550 °C. The optimal Pd loading was found to be 3 wt.%, and it was rationalized in terms of favorable surface Pd dispersion, since above this critical level of 3% an appreciable amount of PdO phase was formed. The reactivity of the optimal 3 wt.% Pd/Co 3 O 4 catalyst from one-shot solution combustion synthesis was evaluated with the aim of optimizing the synthesis procedure. [ABSTRACT FROM AUTHOR]

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over calcined hydrotalcite like compounds containing different combinations of bivalent (Co, Pd, Mg) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co precipitation under low supersaturation conditions and characterized by XRD and TG/DSC. The mixed oxides derived after calcination at 723 K were characterized by XRD, N2 adsorption at 77 K, and XRF. The presence of Rh, La, or Pd in the Co based HTlc's improves considerably the catalytic activity. Co–Rh,Al HTlc (Co/Rh/Al==3/0.02/1) proved to be a very active catalyst, although the presence of the noble metal Pd in this catalyst ex Co,Pd–La,Al HT (Co/Pd/La/Al=3/1/1/1) produces a similar catalytic activity to that of Rh containing catalyst, both in a N2O containing stream and in one containing also SO2 and O2, but with a better performance in stability tests. PdO phase has been identified by XRD as being responsible for the considerable improvement in the activity. The presence of Mg as spinel structure exerts a stabilizing effect in the more active catalysts when mixtures of SO2 and O2 are considered. [ABSTRACT FROM AUTHOR]