Development of Aluminum-Gallium Mixed Oxide Catalysts for Selective Catalytic Reduction of NOx with methane

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Glycothermal synthesis of Ga2O3-Al2O3 solid solution was explored and it was found that the reaction of mixtures of aluminum isoproxide and gallium acetylacetonate in 1,4-butanediol or 1,5-pentanediol at 300℃ for 2 h yielded gamma-type Ga2O3-Al2O3 mixed oxides having a defect spinel structure, in which gallium ions selectively occupy the tetrahedral sites while aluminum ions preferentially occupy the octahedral sites. The Ga2O3-Al2O3 catalyst prepared by the glycothermal method had higher activity than those prepared by the corprecipitation or sol-gel method for selective catalytic reduction of Nox with methane. The activity of the catalyst prepared by the glycothermal method correlated with the ratio of the tetrahedral Ga ions to the total Ga ions and therefore it was concluded that the tetrahedral Ga ions with Al ions at the next-nearest-neighbor sites is the active site for the reaction. B-or Zn-modified solid solutions prepared by the addition of trimethyl borate or zinc acetate to … More the above-mentioned glycothermal reaction also had high activities for the deNOx reaction with methane. For the Zn-modified Ga2O3-Al2O3 catalyst, the modification rather reduced the population of the tetrahedral Ga sites but increased the crystallinity of the catalyst, which reduced the amount of adsorbed water, thus reducing the inhibitory effect of water caused by competitive adsorption of water with Nox or methane. In the selective catalytic reduction of Nox with methane, activation of methane is the rate-determining step and water is strongly adsorbed on the catalysts, thus inhibiting the catalytic activity. Therefore, the catalyst with high crystallinity had high activity. The solvothermal synthesis of the Ga2O3-Al2O3 mixed oxide in various solvents was examined and it was found that the reaction in diethylenetriamine gave the mixed oxide with high crystallinity. The catalyst prepared in diethylenetriamine had a quite high activity for selective catalytic reduction of Nox with methane. Less