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Three‐Dimensional Mesoporous Gallosilicate with Pm 3 n Symmetry and its Unusual Catalytic Performances
Author(s) -
Srinivasu Pavuluri,
Vinu Ajayan
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701946
Subject(s) - mesoporous material , catalysis , materials science , chemical engineering , molecular sieve , hexamethylenetetramine , magic angle spinning , scanning electron microscope , high resolution transmission electron microscopy , specific surface area , transmission electron microscopy , crystallography , nanotechnology , chemistry , nuclear magnetic resonance spectroscopy , organic chemistry , engineering , composite material
Three‐dimensional, mesoporous‐cage‐type, GaSBA‐1 materials with different n Si / n Ga ratios have been successfully prepared for the first time by using a low hydrochloric acid to silicon ( n HCl / n Si ) molar ratio in the synthesis gel by templating with cetyltriethylammonium bromide as the structure‐directing agent in a highly acidic medium. The obtained materials have been unambiguously characterized in detail by several sophisticated techniques including X‐ray diffraction (XRD), N 2 adsorption, high‐resolution transmission electron microscopy, high‐resolution scanning electron microscopy, energy dispersive spectroscopy, elemental mapping, and 29 Si magic‐angle‐spinning NMR spectroscopy. XRD and nitrogen adsorption results reveal that the structures of the GaSBA‐1 materials resemble that of SBA‐1, which possesses a cubic, three‐dimensional, cage‐type structure with open windows. In addition, the specific surface area and the specific pore volume of the GaSBA‐1 materials are much higher than those of the SBA‐1 silica, which are very important for the catalytic applications. The amount of Ga cation in the SBA‐1 silica framework has been found to play a critical role in controlling the morphology and the pore diameter of the materials. Finally, the catalytic activity in the tert ‐butylation of phenol with tert ‐butanol as the alkylating agent has been investigated and the results are compared with those of other mesoporous catalysts such as AlMCM‐41, FeMCM‐41, FeAl‐MCM‐41, and FeSBA‐1. Moreover, the effect of various reaction parameters such as the reaction temperature, reactant feed ratio, and time‐on‐stream on the phenol conversion in the tert ‐butylation of phenol over GaSBA‐1 catalysts has been demonstrated. Among the catalysts examined, GaSBA‐1(17), in which the number in the parenthesis denotes the n Si / n Ga ratio, showed remarkable activity with a high conversion of phenol and selectivity to 4‐ tert ‐butylphenol; it was found to be superior over other mesoporous catalysts used in the study.