Role of acidity and hydrophobicity in the remarkable catalytic activity in water of sulfonic acid-functionalized phenyl-PMO materials

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• 作者：Cl谩udia Bispo ; Paula Ferreira ; Adeline Trouv茅 ; Isabelle Batonneau-Gener ; Fei Liu ; Fran莽ois J茅r么me ; Nicolas Bion
• 关键词：Heterogenous catalysis ; Periodic mesoporous organosilica (PMO) ; Sulfonic acid-functionalization ; Brø ; nsted acidity ; Hydrophobic index (HI) ; FTIR spectroscopy
• 刊名：Catalysis Today
• 出版年：December, 2013
• 年：2013
• 卷：218-219
• 期：Complete
• 页码：85-92
• 全文大小：818 K

文摘

Periodic mesoporous benzene-silica (Ph-PMO) are interesting materials for catalytic applications due to their high surface area, meso- and molecular-scale order, high organic content in the wall and alternated hydrophobic-hydrophilic behavior. Then, propylsulfonic acid-functionalized Ph-PMO material (Ph-PMO-PrSO₃H) is a very active acid solid for catalyzing aqueous organic reaction. Acid strength and hydrophobic properties are usually suggested to explain the distinct behavior of Ph-PMO-PrSO₃H compared to the less active propylsulfonic acid-functionalized periodic mesoporous silica catalysts (PMS-PrSO₃H). Here we present a systematic study in which, the catalytic performances in the reaction of indole with benzaldehyde of propylsulfonic acid-functionalized SBA-15 (SBA-15-PrSO₃H) and Ph-PMO-PrSO₃H are compared. The causes of the different activities are investigated. The strength of the Br酶nsted acidity of the sulfonic acid groups SO₃H are characterized by adsorption of 2,6-dimethylpyridine (DMP) monitored by FTIR spectroscopy. The hydrophobic index (HI) of each solid is determined by water/toluene competitive adsorption. The calculation of the turnover frequencies (TOFs) enables to show that, among all the samples studied, Ph-PMO-PrSO₃H exhibit the higher catalytic activity. The TOF depends on the SO₃H loadings. The aromatic phenyl rings that composed the mesoporous hybrid organosilica walls of the Ph-PMO-PrSO₃H materials does not confer to the sulfonic groups a stronger acidity since a very low difference was observed between the 谓_8a vibration wavenumbers of the DMPH⁺ molecule of SBA-15-PrSO₃H and Ph-PMO-PrSO₃H catalysts. The strength of the acid sites is influenced by the close SiOH or SO₃H environment. The HI values are slightly superior for Ph-PMO-PrSO₃H solid than for SBA-15-PrSO₃H sample even when trimethylsilyl groups are incorporated in this latter catalyst. The HI values decrease a lot as a function of increasing concentration of hydrophilic SO₃H groups.