**4. Conclusions**

In this chapter, we reviewed our previous works of fabrication and morphology control of the hollow spheres and functionality of the hollow spheres. The hollow silica-alumina composite spheres show unexpected high activity for hydrolytic dehydrogenation of ammonia borane compared with the silica-alumina composite fine particles though the ratio of active fourcoordinated aluminum species of the hollow spheres was not significantly high compared with that of the fine particles. From the result of NH<sup>3</sup> -TPD, the hollow spheres possessed higher number of strong Brønsted acid sites, which are effective for hydrolytic dehydrogenation of ammonia borane, than the fine particles. It possibly depends on micro- and/or mesointerparticles spacing, which was formed by the primary particles consisting of the shell of the hollow spheres, and it is suggested that the integrated surface acid sites showed unexpectedly strong acid property.

[2] Rhee DK, Jung B, Kim YH, Yeo SJ, Choi SJ, Rauf A, Han S, Yi GR, Lee D, Yoo PJ. Particlenested inverse opal structures as hierarchically structured large-scale membranes with tunable separation properties. ACS Applied Materials & Interfaces. 2014;**6**:9950-9954 [3] Su BL, Sanchez C, Yang XY. Hierarchically Structured Porous Materials: From Nanoscience to Catalysis, Separation, Optics, Energy, and Life Science. Weinheim: Wiley-VCH Verlag

Role of Interparticle Space in Hollow Spheres of Silica-Based Solid Acids…

[5] Wang DY, Möhwald H. Template-directed colloidal self-assembly – The route to 'topdown' nanochemical engineering. Journal of Materials Chemistry. 2004;**14**:459-468 [6] von Freymann G, Kitaev V, Lotsch BV, Ozin GA. Bottom-up assembly of photonic crys-

[7] Vogel N, Retsch M, Fustin CA, Del Campo A, Jonas U. Advances in colloidal assembly: The design of structure and hierarchy in two and three dimensions. Chemical Reviews.

[8] Gröschel AH, Walther A, Löbling TI, Schacher FH, Schmalz H, Müller AHE. Guided hierarchical co-assembly of soft patchy nanoparticles. Nature. 2013;**503**:247-251

[9] Tanaka Y, Sawamura N, Iwamoto M.Highly effective acetalization of aldehydes and ketones with methanol on siliceous mesoporous material. Tetrahedron Letters. 1998;**39**:9457-9460

[10] Iwamoto M, Tanaka Y, Sawamura N, Namba S. Remarkable effect of pore size on the catalytic activity of mesoporous silica for the acetalization of cyclohexanone with metha-

[11] Yamamoto T, Tanaka T, Funabiki T, Yoshida S. Acidic property of FSM-16. Journal of

[12] Itoh A, Kodama T, Maeda S. Masaki Y. Selective acceleration for deprotection of benzyl ethers with Ti-HMS. Tetrahedron Letters. December, 1998;**39**:9461-9464 ISSN 0040-4039

[13] Greene TW, Wuts PGM. Protective Groups in Organic Synthesis. 2nd ed. New York:

[14] Strukul G. Lewis acid behavior of cationic complexes of palladium(II) and platinum(II):

[15] Urabe H, Sato F. In: Yamamoto H, editor. Lewis Acids in Organic Synthesis. Wiley-VCH:

[16] Thomas JM, Terasaki O, Gai PL, Zhou W, Gonzalez-Calbet J. Structural elucidation of microporous and Mesoporous catalysts and molecular sieves by high-resolution electron

[17] Trikalitis PN, Rangan KK, Bakas T, Kanatzidis MG. Varied pore organization in meso-

]4− anion. Nature. 2001;**410**:671-675

Some examples of catalytic applications. Topics in Catalysis*.* 2002;**19**:33-42

microscopy. Account of Chemical Research. 2001;**34**:583-594

structured semiconductors based on the [SnSe<sup>4</sup>

nol. Journal of American Chemical Society. 2003;**125**:13032-13033

electrodes for dye-sensitized

http://dx.doi.org/10.5772/intechopen.71307

231

GmbH & Co. KGaA; 2011. ISSN: 978-3-527-32788-1

tals. Chemical Society Reviews*.* 2013;**42**:2528-2554

solar cells. Langmuir. 2012;**28**:9372-9377

Physical Chemistry B. 1998;**102**:5830-5839

John Wiley & Sons; 1991. p. 178

Weinheim; 2000. p. 653

2015;**115**:6265-6311

[4] Cho CY, Moon JH. Hierarchical twin-scale inverse opal TiO<sup>2</sup>

The activity of the hollow spheres for hydrolytic dehydrogenation of ammonia borane improved with increasing dispersion of active aluminum species and increasing four-coordinated aluminum species. We previously investigated the influence of various preparation conditions of the hollow spheres to improve the dispersion of the aluminum species and the activity for hydrolytic dehydrogenation of ammonia borane and aluminum precursor that significantly influence both on the dispersion and the activity. The number of Brønsted acid sites and ratio of four-coordinated aluminum species of the hollow spheres prepared using aluminum precursors with the branched alkyl groups was significantly higher than those of the hollow spheres prepared using aluminum precursors with the normal alkyl groups, and then the activity of the hollow spheres prepared using aluminum precursors with the branched alkyl groups was significantly higher than those of the hollow spheres prepared using aluminum precursors with the normal alkyl groups. These results indicate that the hollow spheres with well-ordered pore structure and well-dispersed active aluminum species are expected to show significantly high activity for the hydrogen evolution reaction.
