Effect of modification by alkali on the γ-Ga₂O₃–Al₂O₃mixed oxides prepared by the solvothermal method

Abstract

The solvothermal reaction of the mixtures of aluminium triisopropoxide (AIP) and gallium triacetylacetonate at 300 • C directly yielded γ -Ga 2 O 3 -Al 2 O 3 mixed oxides (solid solutions, but Ga 3+ ions preferentially occupied the tetrahedral sites of the defect spinel structure). The reaction of AIP alone in 2-(methylamino)ethanol yielded γ -Al 2 O 3 , and the reaction of the mixture of AIP and Ga(acac) 3 yielded γ -Ga 2 O 3 -Al 2 O 3 mixed oxides having an Al ratio identical to the charged ratio. Although the reaction of AIP alone in toluene at 315 • C yielded χ-Al 2 O 3 , the reaction at 300 • C gave an amorphous product, while the reaction of Ga(acac) 3 alone afforded γ -Ga 2 O 3 at 300 • C. The reaction of the mixtures of the two starting materials yielded the γ -type mixed oxide even with extremely high charged ratio of Al. It was concluded that, in toluene, the initial formation of γ -Ga 2 O 3 nuclei controlled the crystal structure of the mixed oxide. The mixed oxide catalysts with lower acid density showed lower methane consumption by combustion in selective catalytic reduction of NO with methane. By alkali modification of the catalyst, the acid density of the mixed oxide decreased, and the CH 4 combustion rate was diminished. Although NO conversion activity was also decreased by the modification, the efficiency of methane used for NO reduction was improved.

Synthesis of Gallium–Aluminum Dawsonites and their Crystal Structures

“…The activity of the catalyst prepared solvothermally using various solvents depended on the crystallite size of the catalyst. The catalyst with a large crystallite size had high catalytic activity in spite of the fact that the catalyst had low surface area 46 . We recently found that calcination of the precursors obtained by coprecipitation of gallium and aluminum nitrates with ammonium carbonate yielded well‐crystallized γ‐Ga 2 O 3 –Al 2 O 3 solid solutions, which also showed high catalytic activities for methane‐SCR of NO 47 .…”

Synthesis of Ga2O3–Al2O3 Catalysts by a Coprecipitation Method for CH4-SCR of NO

“…Catalytic tests for the SCR of NO with methane were carried out in a fixed-bed flow reactor [1]. The catalyst was tabletted, pulverized into 10-22 mesh, and set in the reactor.…”

“…We have reported that the catalyst containing a small amount of Na ? ions showed low NO conversion [1], and therefore the amorphous precursor prepared with NaHCO 3 may occlude Na ? ions, thereby destroying the catalyst activity of the c-Ga 2 O 3 -Al 2 O 3 catalyst.…”

“…We have reported that c-Ga 2 O 3 -Al 2 O 3 catalysts prepared by the solvothermal method using diethylenetriamine as a solvent showed very high activities for SCR of NO with methane as a reducing agent (CH 4 -SCR of NO) under both dry and wet conditions [1]. However, synthesis of a large amount of the catalyst by this method is not easy and needs a large amount of the organic solvent.…”

Direct formation of spinel-structured γ-Ga2O3-Al2O3 nanoparticles by a mild hydrothermal method

“…Gallium oxide-based materials have attracted considerable attentions, and they have been applied for catalysts [3][4][5][6], gas sensors [7,8], phosphors [9], spintronics devices [10], and transparent electronic devices [11]. The studies on the formation and properties of gallium oxide-based materials have been conducted using various synthesis methods, e.g., coprecipitation [12], solvolysis of GaCl 3 in N, N-dimethylformamide [13], pulsed-laser deposition technique [14], calcination of gels [15], hydrothermal method [16], solvothermal or glycothermal technique [17,18], and colloidal synthesis route [19,20]. The catalytic properties of copper-doped gallium oxide with spinel-type structure formed through microwave hydrothermal method have been reported, but its crystallinity was very low [21].…”