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Cesium-promoted cobalt spinel is promising as a catalyst for the low-temperature decomposition of nitrous oxide for use in the second stage of a single-reactor unit for the combined removal of nitrogen oxides. This work studied the effect of the conditions for the preparation of granular and block bulk catalysts based on Co3O4 by extrusion molding. [ABSTRACT FROM AUTHOR]

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 potassium or cesium doped ZnCoO|AlO catalysts with different alkali loadings were prepared, characterized with respect to chemical composition (XRF), structure (XRD, RS) morphology (TEM), and the alkali promoter thermal stability. A strong beneficial effect on the deNO activity of the ZnCoO|AlO catalyst (decrease in the T by about 80 °C) was observed for both promoters at different surface coverages. It was found that in comparison to a rather narrow range of optimal cesium loading (0.5-2 atoms/nm) a comparable promotional effect of potassium doping was observed for a slightly wider surface concentrations (0.5-3 atoms/nm). Such difference was attributed to surface dispersion of potassium over the alumina support and the spinel active phase, while cesium was found to be located mainly on the spinel phase. For practical applications, the superiority of potassium over cesium consist in fact that a similar beneficial effect is associated with much higher thermal stability in the temperature range of the catalyst deNO operation and lower price of the promoter precursor. [ABSTRACT FROM AUTHOR]

In this work, a series of CoO spinels were produced by different synthesis routes (precipitation, solution combustion synthesis, and hard template method), and were used as non-noble catalysts for the oxygen evolution reaction (OER) under basic conditions. The investigated catalysts have a proportional relation between electrochemical activity, surface roughness, and specific surface area. The hard template synthesis method resulted in the most active catalyst compared in this work, which we ascribe to its highly porous structure, and concomitant Co/Co redox couple at a lower potential, attributed to the OER. The most performant catalyst was compared with a commercial catalyst (Ni@NiO, Alfa Aesar) showing only 0.01 V overpotential difference, evaluated at 10 mA cm (overpotential 0.44 V). Graphical Abstract: [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]

The influence of Zn and K promoters on N2O decomposition over Co3O4 was investigated by work function measurement and temperature-programmed surface reaction. The beneficial effect of the promoters resulting in spectacular decrease in the temperature of 50% conversion by 200 °C was found to be essentially of electronic origin. The strong correlation between the catalyst work function and deN2O activity allowed for the optimization of the doping level of both additives. The pilot plant tests in real nitric acid tail gases revealed that the optimized double promoted (Zn, K) cobalt spinel catalyst maintained its remarkable activity in N2O decomposition (conversion >95% at the target temperature of 350 °C) for more than 60 h. [ABSTRACT FROM AUTHOR]

The beneficial effect (decrease of the half conversion temperature by 100 °C) of potassium doping, in the range of 0–5 atoms/nm2, on N2O decomposition over Co3O4 was analyzed by work function measurements and DFT calculations. The optimal potassium surface loading was found to be 1.8 atoms/nm2. The effect was explained in terms of electronic promotion gauged by lowering of the catalyst work function by 0.48 eV (for K2CO3 precursor) and 0.44 eV (for KOH). The promotional effect is discussed in relation to the theoretical and experimental surface dipoles determined from Hirshfeld atomic charges and geometry of the postulated potassium adspecies and from the Topping model, respectively. [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]