2015 年 40 巻 2 号 p. 179-182
In this work, we investigated the influence of the pH condition during the impregnation process on the immobilization of molybdosilicic acid on hollow silica spheres and their activity for hydrolytic dehydrogenation of ammonia borane. To adjust the pH, amino acids such as L-aspartic acid and L(+)-arginine were added to the impregnating solution. Transmission and scanning electron microscopy showed that samples prepared at lower pH consist of homogeneous hollow silica spheres while those prepared at higher pH include collapsed hollow spheres. The activity for hydrogen evolusion from aqueous NH3BH3 solution depends on the catalyst; the molar ratios of the hydrolytically generated hydrogen to the initial NH3BH3 were 2.0, 1.3, 1.3, and 1.0 at pH = 4.0, 6.0, 8.0, and 9.7, respectively. After the reaction, the sample prepared at lower pH had a higher valence value of Mo species according to results from X-ray photoelectron spectroscopy, and the corresponding amount of Mo species in the reaction solution was also lower. The results indicated that the molybdosilicic acid supported on homogeneous hollow silica spheres had a higher valence value of Mo species and the effectively immobilized acid had a higher activity for hydrogen evolusion from aqueous NH3BH3 solution.
