Synthesis and catalytic properties of mesoporous phosphotungstic acid/SiO_2 in a self-generated acidic environment by evaporation-induced self-assembly

摘要

Well-ordered mesoporous phosphotungstic acid/SiO_2 (HPW/SiO_2) with Keggin-type heteropolyacids (HPAs) encapsulated into SiO_2 framework has been synthesized by evaporation-induced self-assembly method. The main strategy of this method is to utilize the acidity self-generated of phosphotungstic acid (HPW) as the catalyst for tetraethoxysilane (TEOS) hydrolysis. The TEOS hydrolysis leads to forming the positive charge silicate species that can combine with HPW anion to form colloidal Si-HPW entities resulting from the static interaction. These Si-HPW entities can be assembled to form mesostructure with solvent evaporation. There is almost no leaching of HPW into ethanol when the samples are treated in boiling ethanol for 3 h. Results of catalytic tests show that mesoporous HPW/SiO_2 materials have excellent catalytic activities in the oxidative desulfurization of bulky molecule dibenzothiophen, and there are almost no activity losses even after fifth cycle of uses.