Effect of modification by alkali on theγ-Ga2O3–Al2O3 mixed oxides prepared by the solvothermal method

Abstract

The solvothermal reaction of the mixtures of aluminium triisopropoxide (AIP) and gallium triacetylacetonateat 300 °C directlyyielded γ-Ga2O3–Al2O3 mixed oxides(solid solutions, but Ga3+ ions preferentially occupied the tetrahedral sites of the defect spinelstructure). The reaction of AIP alone in 2-(methylamino)ethanol yieldedγ-Al2O3, and the reaction of the mixture of AIP andGa(acac)3 yielded γ-Ga2O3–Al2O3 mixedoxides having an Al ratio identical to the charged ratio. Although the reaction of AIP alone in tolueneat 315 °C yielded χ-Al2O3, thereaction at 300 °C gave an amorphous product, while the reaction ofGa(acac)3 aloneafforded γ-Ga2O3 at 300 °C. The reaction of the mixtures of the two starting materials yielded theγ-type mixed oxide even with extremely high charged ratio ofAl. It was concluded that, in toluene, the initial formation ofγ-Ga2O3 nuclei controlled the crystal structure of the mixed oxide. The mixed oxidecatalysts with lower acid density showed lower methane consumption bycombustion in selective catalytic reduction of NO with methane. By alkalimodification of the catalyst, the acid density of the mixed oxide decreased, and theCH4 combustion rate was diminished. Although NO conversion activity was also decreased bythe modification, the efficiency of methane used for NO reduction was improved.