Recent Research Report

Synthesis and characterization of Novel Ionic liquid templated ordered mesoporous hexagonal and cubic aluminosilicates

Maddila A. Kumara, Nunna V. Krishnaa and Parasuraman Selvama,b

aNational Centre for Catalysis Research,Department of Chemistry, Indian Institute of Technology-Madras, Chennai 600 036, India

bNew Industry Creation Hatchery Centre, Tohoku University, Sendai 980 8579, Japan

E-mail:

Keywords: Mesoporous aluminosilicates, AlIITM-41, AlIITM-48, Ionic liquid, C16mimCl, Tertiary-butylation, Phenol.

Highly ordered mesoporous aluminosilicates (OMAS), viz., AlIITM-41 and AlIITM-48, having hexagonal and cubic pore structure, respectively with varying silicon-to-aluminium ratios were hydrothermally synthesized under basic medium using long chain ionic-liquid such as 1-hexadecyl-3-methylimidazolium chloride (C16mimCl) as templating agent. The prepared materials exhibit moderate pore size, thicker walls and highly stable framework structure. All the samples were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, BET, TEM and XRF. In addition, 27Al MAS-NMR and NH3-TPD measurements were performed to check the extent of aluminium incorporation and the nature of acidic sites in the framework structure. The quality of these materials were compared with analogous AlMCM-41and AlMCM-48. It was found that the ionic liquid template materials, exhibits superior properties than the latter in terms of crystallinity, surface area, pore volume and wall thickness as well as the extent of incorporation trivalent aluminium ions exclusively in the silicate matrix (Figure 1 and Table 1). The exceptional properties of the AlIITM-41 and AlIITM-48 catalysts over the corresponding AlMCM-41 and AlMCM-48 is attributed to the superior micellar structure characteristics with well distributed positive charge and - stacking of aromatic imidazolium head group of ionic-liquid results in thicker walls, huge surface area, large pore volume and high crystallinity of the synthesized materials. As a result, the proton-exchanged materials, i.e., H-AlIITM-41 and H-AlIITM-48, possess excellent Brønsted acidity. This, in turn, greatly influences the catalytic activity, e.g., tertiary-butylation of phenol reaction (nor reproduced here).

Figure 1.XRD patterns of calcined AlIITM-41 (A) and AIITM-48 (B) with varying silica-to-alumina ratios: (a) ∞; (b) 90; (c) 60; (d) 30; (e) 10.

Table 1. Structural and textural properties of various mesoporous aluminosilicates.

Catalyst a / a0
(nm) / SBET
(m2g1) / D
(nm) / Vp
(cm3 g1) / hwb
(nm)
AlIITM-41 / 4.85 / 745 / 2.7 / 1.40 / 2.11
AlMCM-41 / 4.50 / 831 / 2.8 / 1.17 / 1.70
AlIITM-48 / 9.85 / 1184 / 2.9 / 1.09 / 1.73
AlMCM-48 / 9.65 / 950 / 2.8 / 0.67 / 1.60

Acknowledgments:The authors thank DST, New Delhi for funding NCCR, IIT-Madras.

References

[1]P. Selvam, S. K. Bhatia, C. G. Sonwane, Ind. Eng. Chem. Res., 2001, 40, 3237.

[2] C. J. Adams, A. E. Bradley, K. R. Seddon, Aust. J. Chem., 2001, 54, 679.

[3] M.A. Kumar and P. Selvam, Adv. Porous Mater.,2015, 3, 1.