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A range of mesoporous gallosilicate molecular sieves with the MCM-41 structure have been synthesized using gallium nitrate as the source of gallium and characterized in detail by elemental analysis, XRD, 71Ga and 29Si MAS NMR, N2 adsorption measurements, and TEM. The quality of the products is very sensitive to the pH of the gel mixture. Atomic absorption and XRD show that Ga and Si in the gel are incorporated into the MCM-41 structure in nearly equal proportions. 71Ga and 29Si NMR demonstrate that in all as-made samples gallium is 4-coordinate and forms a part of the MCM-41 structure. Although upon calcination gallium is partially expelled from the structure of samples with Si/Ga ≤ 20, Ga in samples with Si/Ga ≥ 30 is unaffected. N2 adsorption measurements and TEM demonstrate the high mesoporosity of gallosilicate MCM-41-30. The pore size distribution indicates that the structure of sample MCM-41-20 partially collapses upon calcination and macropores are formed.
Cheng et al. (Mon,) studied this question.