多金属氧酸盐／SBA-15介孔杂化材料的稳定性

Stability of Polyoxometalate/SBA-15 Mesoporous Hybrid Materials

采用TG-DTA、XRD、FT-IR、低温N2吸附和ICP-AES等分析测试技术考察了共价固定的SiW11/SBA-15介孔杂化材料的热稳定性、溶剂浸取稳定性和水热稳定性。结果表明,杂化材料中多金属氧酸盐物种SiW11O39[O(SiO-)2]6-的热稳定性比纯SiW11O39[O(SiOH)2]4-化合物略低,在通常的焙烧脱模温度(500℃)下不能稳定存在,分解为SiO2和WO3,因此样品不宜采用焙烧方法脱模。杂化样品中的多金属氧酸盐物种有很强的抗溶剂浸取能力,在常温水溶液中的溶脱流失率远低于浸渍样品,表现出化学固定的优越性。但在高温水溶液中由于Si—O—W键的水解,多金属氧酸盐物种有相当程度的溶脱。水热处理后,杂化材料仍然保持六方介孔结构,孔壁收缩,孔径、孔容增大。多金属氧酸盐物种脱除后介观结构仍然保持的事实表明,这些物种主要键联于孔道内的孔壁表面,没有进入孔壁内的SiO2网络。

The stabilities of polyoxometalate（POM）/mesoporous molecular sieve hybrid material SiW./SBA- 15, including thermal stability, hydrothermal stability and ability against solvent-leaching, were investigated by means of TG-DTA, XRD, FT-IR, N2 adsorption-desorption and ICP-AES. It was found that POM species, SiW. 039 [ O（SiO-） 2 ] ^6-, in the hybrid materials was less stable than the corresponding pure compound and was decomposed into SiO2 and WO3 under the calcination at 500 ℃. Therefore, the calcination should be avoided in the removal of the template. The POM species in the hybrid materials possesses higher stability against solvent-leaching; the percentage of the species lost in water at room temperature is much less than that of POM species in the impregnated samples, exhibiting high immobility of chemically bound species on the support. However, a considerable amount of POM was leached by hot water due to the hydrolysis of Si-O-W bonds. After hydrothermal treatment, the hexagonal mesostructure of the hybrid materials was retained, accompanied by the shrinkage in pore walls and increases in pore size and pore volume. The remains of mesostructure after removing POM species revealed that POM species mostly located on the surface of pore walls rather than within the SiO2 network in walls.