Interaction between Ru and Co3O4 for promoted catalytic decomposition of N2O over the Rux-Co3O4 catalysts

Promotion of Cobalt Oxide Catalysts by Acid-Etching and Ruthenium Incorporation for Chlorinated VOC Oxidation

In this work, Ru-promoted cobalt oxide catalysts with a nanotube morphology were prepared by a synthesis route based on the Kirkendall effect followed by an acid treatment and subsequent optimized Ru impregnation. The resulting samples were thoroughly characterized by means of N2 physisorption, X-ray energy-dispersive spectroscopy, X-ray diffraction, scanning electron microscopy techniques, X-ray photoelectron spectroscopy, and temperature-programmed techniques (O2-temperature-programmed desorption, H2-temperature-programmed reduction, and temperature-programmed oxidation) and evaluated in the gas-phase oxidation of 1,2-dichloroethane. It has been demonstrated that Ru addition improves the oxygen mobility as well as the amount of Co2+ and Oads species at the surface by the formation of the Ru-O-Co bond, which in turn governs the performance of the catalysts in the oxidation reaction. Moreover, the acid-etching favors the dispersion of the Ru species on the surface of the catalysts and strengthens the interaction among the noble metal and the cobalt oxide, thereby improving the thermal stability of the Ru-promoted oxides. Thus, the resulting catalysts are not only active, as the chlorinated pollutant is efficiently converted into deep oxidation products at relatively low temperatures, but also quite stable when operating for 120 h.

Potassium promoted Gd0.06Co catalysts for highly efficient catalytic N2O decomposition in presence of impurity gases at low temperature

In order to enhance the catalytic performance of the Gd-modified Co₃O₄ catalyst (Gd_0.06Co) for the N₂O decomposition, alkali metal K was introduced as the promoter by impregnating the Gd_0.06Co powder with an aqueous solution of KNO₃ (with K/Co ratios 0.01-0.05). With the doping of K, the catalytic activity over Gd_0.06Co was significantly improved and the temperature of N₂O complete decomposition was decreased from 350 °C to 300 °C. Combining the results of XPS and O₂-TPD, the superior catalytic performance of the optimum catalyst K_0.025Gd_0.06Co was mainly owing to the synergistic effect of Gd and K, which weakened the Co-O bond and endowed the catalyst surface with much more amount of oxygen vacancies. Even under the coexist of the impurity gases, such as 5 vol% O₂, 100 ppmv NO and 2 vol% H₂O, the K_0.025Gd_0.06Co catalyst exhibited prominently better catalytic activity than Gd_0.06Co and K_0.025Co catalysts.

Understanding the Iron-Cobalt Synergies in ZSM-5: Enhanced Peroxymonosulfate Activation and Organic Pollutant Degradation

Iron- and cobalt-based heterogeneous catalysts are widely applied for activating peroxymonosulfate (PMS) to degrade organic pollutants. However, few studies have unveiled the clear synergistic mechanism of iron and cobalt in ZSM-5. In this paper, the synergistic mechanism of enhanced PMS activation was revealed by constructing iron and cobalt bimetal modified ZSM-5 zeolite catalysts (FeCo-ZSM-5). The tetracycline hydrochloride (TCH) degradation experiments showed that the catalytic activity of FeCo-ZSM-5-2:3 was much higher than those of Fe-ZSM-5 and Co-ZSM-5. In addition, the influences of catalyst dosage, PMS concentration, reaction temperature, initial pH, and coexisting ions on TCH removal were systematically investigated in this paper. Density functional theory calculations indicated that Co was the main active site for PMS adsorption, and Fe increased the area of Co's positive potential mapped to the electron cloud. The Fe-Co bimetallic doping increased the area of positive potential mapped to the electron cloud and benefited the adsorption of PMS on the catalyst surface, which revealed the synergistic mechanism of bimetals. Electron paramagnetic resonance spectra and quenching experiments showed that sulfate radicals, singlet oxygen, and hydroxyl radicals were involved in the degradation of TCH. Furthermore, liquid chromatography-mass spectrometry was conducted to propose possible degradation pathways. This work provides certain guiding significance in understanding the synergistic effect of heterogeneous catalysts for tetracycline wastewater treatment.

Strong Structural Modification of Gd to Co3O4 for Catalyzing N2O Decomposition under Simulated Real Tail Gases

In this paper, Gd-promoted Co₃O₄ catalysts were prepared via a facile coprecipitation method for low-temperature catalytic N₂O decomposition. Due to the addition of Gd, the crystallite size of Co₃O₄ in the Gd_0.06Co catalyst surprisingly decreased to 4.9 nm, which is much smaller than most additive-modified Co₃O₄ catalysts. This huge change in the catalyst's textural structure endows the Gd_0.06Co catalyst with a large specific surface area, plentiful active sites, and a weak Co-O bond. Hence, Gd_0.06Co exhibited superior activity for catalyzing 2000 ppmv N₂O decomposition, and the temperature for the complete catalytic elimination of N₂O was as low as 350 °C. Meanwhile, compared with pure Co₃O₄, E_a decreased from 77.4 to 46.8 kJ·mol^-1 and TOF of the reaction increased from 1.16 × 10^-3 s^-1 to 5.13 × 10^-3 s^-1 at 300 °C. Moreover, Gd_0.06Co displayed a quite stable catalytic performance in the presence of 100 ppmv NO, 5 vol % O₂, and 2 vol % H₂O.