Alongside TiO2, Magneli-phase titanium suboxide having the composition of TinO2n-1 is a kind of attractive functional materials composed of titanium. However, there still remain problems to be overcome in the synthesis of titanium suboxide; the existing synthesis methods require high temperature typically over 1000 °C and/or post-synthesis purification. This study presents a novel approach to synthesis of titanium suboxide nanoparticles through solid-phase reaction of TiO2 with TiH2. Crystal phases of titanium suboxide were easily controlled by changing TiO2/TiH2 molar ratios in a TiO2-TiH2 mixed precursor and a series of titanium suboxide nanoparticles including Ti2O3, Ti3O5, Ti4O7 and Ti8O15 were successfully obtained. The reaction of TiO2 with TiH2 proceeded at relatively low temperature due to high reactivity of TiH2, giving titanium suboxide nanoparticles without any post-synthesis purification. Ti2O3 nanoparticles and TiO2 were applied as solid acid catalysts for reaction of furfural with 2-propanol. Ti2O3 showed high catalytic activity and high selectivity for acetalization of furfural, while TiO2 showed only poor activity for transfer hydrogenation of furfural. The difference in catalytic properties is discussed in terms of the acid properties of Ti2O3 and TiO2.
Solid base BaO _ Al2O3 catalyst was synthesized using the solid-liquid interface reaction of Ba(OH)2 H2O in the solid phase with Al(OCH(CH3)2)3 dissolved in ethyl acetate. Water of crystallization in the barium hydroxide, Ba(OH)2 H2O was consumed by hydrolysis of Al(OCH(CH3)2)3 into Al2O3 and isopropanols. BaO _ Al2O3 catalyst synthesized by solid-liquid interface reaction of Ba(OH)2 H2O with equal mols of Al(OCH(CH3)2)3 and heat-treated at 673 K showed the highest activity among the prepared catalysts for the retro-aldol reaction of diacetone alcohol. Active BaO _ Al2O3 catalysts with various contents of BaO were obtained by heating at appropriate temperatures just below those of Ba5Al2O8 and BaAl2O4 crystallization. X-ray diffraction analysis detected no BaO phase in this solid base catalyst. Barium oxide highly dispersed in amorphous Al2O3 was prepared by the solid-liquid interface reaction. The interface reaction of metal hydroxide in the solid phase with alkoxide in the liquid phase is useful to form well-dispersed mixed metal oxides.
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