Cobalt-based Composite Oxides For N₂O Decomposition

Nitrous oxide?N₂O?is a powerful greenhouse gas with high Global Warming Potential?GWP?.Furthermore,it is the largest ozone depleting substance in conjunction with very long atmospheric lifetime of around 150 years.Hence,the abatement of N₂O,the hazardous pollutant,attracts extensive research attention recently.Among the catalysts reported for N₂O decomposition,Co-based catalysts have stimulated considerable interests of researchers due to their superior performance.In this thesis,cobalt-based oxides with low cost,good catalytic stability and impurity gas tolerance were designed and synthesized by means of doping additive or loading support.Accordingly,the main contents and results of the thesis are as follows:1.A series of Y-doped Co₃O₄ catalysts were prepared by coprecipitation method and employed for N₂O decomposition.Among the obtained xYCo?x = 0 0.1?catalysts,0.04 YCo exihibited the best catalytic activity.By means of some characterization techniques,the formation mechanism of the catalyst was discussed and the effect of promoter Y on the structure and surface properties of cobalt oxide catalyst was studied.It was found that the addition of Y could not only significantly reduce the average particle size and greatly increase the specific surface area of cobalt oxide,but also increase the number of oxygen vacancies of the catalyst.Furthermore,the tolerance to impurity gases of 0.04 YCo catalyst was investigated,and the inhibition mechanism of impurity gases was studied.The results indicated that 0.01% NO,5% O₂ or 2% H₂O could lead to activity degradation of the catalyst.O₂ or H₂O suppressed the activity of 0.04 YCo by competitive adsorption on active sites of the catalyst,so they influence the reaction just by dynamics.When NO + O₂ coexisted in the feed gas,the activity deactivation was caused by the formation of nitrate species on the catalyst surface.2.Co₃O₄ or Y-doped cobalt oxide was supported on TiO₂ by deposition-precipitation method,thus 0.3Co/TiO₂ and Y0.3Co/TiO₂ catalysts were obtained.The results indicated that Y could improve the dispersion of cobalt oxide on TiO₂ support.Consequently,the activity of Y0.3Co/TiO₂ for the reaction is higher than that of 0.3Co/TiO₂ catalyst.By comparing the catalytic activity and impurity gas tolerance of the catalysts with and without support,it was found that,although Y0.3Co/TiO₂ catalyst was less active for the reaction,it exihibited better tolerance to impurity gas compared to 0.04 YCo catalyst.Y0.3Co/TiO₂ catalyst displayed a higher stable conversion than that of 0.04 YCo catalyst in feed gas of 0.2% N₂O + 0.01% NO + 5% O₂ + 2% H₂O at 400 ?.3.Core-shell type Co0.24Ba?AD?catalyst was prepared by adsorption-deposition method,in which cobalt mainly located on the BaCO₃ surface with small amount of Ba incorporation,i.e.formed a Ba-doped porous active shell on the support.Since the active component for N₂O decomposition primarily presents in the shell,which made the component properly promoted by barium and easily accessed by the reactant molecules,the catalyst exhibited superior activity in comparison with the catalysts possessing traditional structure.Over the Co0.24Ba?AD?catalyst that containing only 8.91 wt% of Co₃O₄,complete N₂O conversion was achieved at 400 ? and 20,000 h-1.