Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

Abstract

By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga 2 O 3 /Al 2 O 3 oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X-ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel-type structure; also shown by γ-Al 2 O 3 and γ-Ga 2 O 3 . The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m 2 g Ϫ1 for the mixed oxide having Ga:Al ϭ 9:1 up to 370 m 2 g Ϫ1 for that having Ga:Al ϭ 1:9. High resolution MAS NMR showed that Ga 3ϩ and Al 3ϩ ions occur at both tetrahedral and octahedral sites in the spinel-type structure of

Enhanced Activity of Spinel-type Ga2O3–Al2O3 Mixed Oxide for the Dehydrogenation of Propane in the Presence of CO2

“…Taking both yield of propylene and the catalyst stability into account, 773 K could be the most appropriate temperature for the propane dehydrogenation reaction over Ga 2 O 3 -Al 2 O 3 mixed oxides. a-, b-, and d-Ga 2 O 3 , are known to be present depending upon the treatment conditions [24,25]. It also can be observed that the diffraction peaks were rather broad that suggested a poor crystallinity nature of the mixed oxide samples, which has already been reported to be a common feature of the metastable c-variety of both alumina and gallia polymorphs [24,25].…”

“…Broadness notwithstanding, the diffraction maxima evidenced in the XRD patterns of the gallia-alumina samples could be assigned to a single phase having the cubic spineltype structure (space group Fd3m) [24] as shown by the indexing in Fig. 4.…”

“…a-, b-, and d-Ga 2 O 3 , are known to be present depending upon the treatment conditions [24,25]. It also can be observed that the diffraction peaks were rather broad that suggested a poor crystallinity nature of the mixed oxide samples, which has already been reported to be a common feature of the metastable c-variety of both alumina and gallia polymorphs [24,25]. It was also expected as a result of the high surface area of the mixed Ga 2 O 3 -Al 2 O 3 samples, for which nitrogen adsorption isotherms at 77 K gave BET surface area values ranging from 119 m 2 /g, for the sample having a nominal Ga:Al ratio of 4:1, to 147 m 2 /g for Ga:Al = 1:4 (Table 1).…”

“…A series of Ga 2 O 3 -Al 2 O 3 mixed oxide catalysts with various compositions as well as the simple oxide of Al 2 O 3 and Ga 2 O 3 were prepared through an alcoholic coprecipitation pathway [24]. In a typical synthesis, concentrated aqueous ammonia and ethanol (50:50 in volume) was added dropwise to the ethanol solution of gallium nitrate hydrate (Aldrich, 99.99%) and aluminum nitrate hydrate (Fluka, 99.9%) with different Ga:Al molar ratio until no more precipitation occurred.…”

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].…”